This report presents a tool for relicensing participants to determine appropriate scientific methods to measure and predict the effects of hydropower projects on ecological resources. This tool is expected to be most useful during the development of study plans (see Project Overview), and during the process of requesting additional studies after the preparation of the final license application. For each type of project effect identified in the Project Effects Matrix, this evaluation outlines the types of scientific approaches based on the best available science to address specific effects. Each of these methods is described and evaluated, including identification of its limitations and suggestions for selecting the most appropriate method based on site-specific considerations. This is not a laundry list of all potential approaches that are available to evaluate a particular effect. Emphasis is placed on describing those approaches that are proven and accepted, and on identifying current or new technologies and methods. Although each resource area is discussed independently of the others, studies are typically most successful if approached in an integrated manner, considering a holistic view of the project and its potential effects on the environment. Often appropriate studies can be selected most efficiently when the project is viewed as part of a larger system, culminating in an integration of the results of individual studies.
This report emphasizes those studies that directly assess project effects. Studies, for example, that address appropriate management of the project (e.g., establishing ramping rates), or are designed to select appropriate mitigations (e.g., fish passage feasibility analysis), are either not included, or discussed only briefly. In addition, approaches to assessing interdependent and interrelated effects that would not occur but for the existence of the hydropower projects (e.g., levees as mitigations for flood control projects) are not included. However, for each project there are often multiple affiliated facilities, each with their own effects. Some of these facilities operate in tandem with the hydropower facility that may or may not be a function of the hydropower license, most recognizably hatcheries (see Williams et al. 2003). We do not address hatcheries or other facilities with such highly variable relationships to hydroelectric projects here.
In this evaluation some topics and resource areas are given a higher priority for discussion than others, based on three general guidelines. First, this report focuses on issues for which a comparison of alternative approaches would be most useful. For example, since the methods for collecting water temperature data are relatively standard, limited attention is given to temperature collection methods. In contrast, multiple methods for examining sediment transport, instream flows, and fish entrainment have been developed, none of which can be considered standard. This report provides a comparison of approaches in these arenas for which a standard approach is not evident.
Secondly, for many of the resources discussed in this report, the first phase of evaluating project effects typically involves taking a basic inventory of existing resources-that is, conducting surveys to identify, map, and characterize the resources in the project area. These types of inventories include fish species composition and distribution surveys, archeological artifact surveys, botanical species and vegetation community mapping, wildlife species surveys, water temperature monitoring, geomorphic terrains mapping, and large woody debris surveys. Under the relicensing process and associated National Environmental Policy Act (NEPA) and/or Endangered Species Act (ESA) process, information from these types of surveys is used in a risk assessment to determine if the sensitive resources are, or could be, disturbed by the project. Although these surveys are crucial, the approaches they employ are not unique to hydroelectric projects. This report does not discuss methods for basic resource inventories. Instead, it focuses on approaches that are specifically designed to evaluate effects of hydroelectric projects, while still recognizing the importance of general survey data.
Thirdly, this report emphasizes issues and scientific approaches pertaining to the effects of hydroelectric projects on rivers and associated aquatic ecosystems. While terrestrial resources (e.g., plants, wildlife) and cultural, recreational, and aesthetic resource studies are briefly discussed, they are not evaluated at the same level of detail as fisheries, hydrology, fluvial geomorphology, and water quality studies are. The structure of the report sections also varies among resource areas, reflecting the level of emphasis on a particular resource area. It is our hope that by emphasizing aquatic resource issues and studies, this report will be most useful to participants in the hydroelectric relicensing process.
This document is not intended to provide the complete methods, or "cookbook" for any of the approaches discussed, but rather is intended to point out and in some cases compare a variety of approaches. Selected references to the scientific literature are provided to enable the reader to obtain additional details on the methods used for each approach, as well as their successful application. As this document illustrates, there is not a one-size-fits-all scientific approach to studying any given effect of hydroelectric projects. To help the reader evaluate which approaches might be best suited for a particular project, information is provided for some types of studies on the advantages, disadvantages, and site-specific considerations and applicability of many of the scientific methods. However, it is not possible to provide all of the criteria in this report that a relicensing participant could consistently and definitively use to select the appropriate study approach in all potential scenarios. It is typically the responsibility of the resource specialist involved to explain and defend the approaches selected, and at a minimum, it is the intention of this document to provide enough background information for a participant to judge and respond to the selection. Sometimes a combination of approaches is required to evaluate a given project effect. Also, external limitations such as financing or social priorities may drive study selection and development.
Hydroelectric projects potentially affect many aspects of water quality, as outlined in the Project Effects Matrix (Part I). The Clean Water Act of 1972 (33 USC § 1251 et seq), originally adopted in Public Law 92-500, requires each state to develop criteria protective of water quality. To do this, the Environmental Protection Agency and states examine the effects of specific pollutants on plankton, fish, shellfish, wildlife, plants and recreational activities and determine the levels of pollutants that can exist without harming human and aquatic life. The states then determine the most beneficial designated use(s) of a particular water body (most often aquatic species and drinking water supply), and adopt water quality criteria designed to protect these uses as well as more general provisions that protect against water quality degradation.
Dams, turbines, power lines, roads, and operations and maintenance all have some potential impact on water quality. Although watershed land uses and the potential impacts of past and ongoing discharges of anthropogenic contaminants must be taken into consideration in the development of any water quality sampling plan, the most common effects of hydroelectric projects are changes in the physical structure of the aquatic ecosystem. The most pronounced effects associated with hydroelectric operations are related to dams, such as increased sediment accumulation, alterations in temperature regimes in bypass reaches and the tailraces of powerhouses, reductions in dissolved oxygen, and increases in some pollutants such as hydrogen sulfide, nutrients, and manganese. A variety of approaches are discussed below to evaluate specific effects of hydroelectric projects on water quality, including:
These are not all of the potential effects of hydroelectric projects on water quality, and the methods to evaluate them by no means cover all the potential approaches that could be used to study the effects. Rather, this discussion focuses on those effects where a nexus to project effects is most distinct and where approaches to evaluate effects are not necessarily standardized. The following references are recommended for additional information on general water quality and limnological monitoring techniques that may be employed to assess both existing water quality problems related to hydroelectric project operations, or possibly to identify emerging trends towards future degradation.
2.1.1 Selected references
Allan, J. D. 1995. Stream ecology: structure and function of running waters. First edition Chapman and Hall. New York.
Barbour, M. T., J. Gerritsen, B. D. Snyder, and J.B. Stribling. 1999. Rapid bioassessment protocols for use in streams and wadeable rivers: periphyton, benthic macroinvertebrates, and fish. Second edition. EPA 841-B-99-002. U. S. Environmental Protection Agency, Office of Water, Washington, D. C.
Wetzel, R. G. 2001. Limnology: lake and river ecosystems. Academic Press, San Diego,California.
Virtually all biological and ecological processes are affected by water temperature. Not only does temperature directly influence chemical equilibria, but invertebrate and fish communities are also extremely sensitive to temperature. In terms of effects on biota, water temperature has direct but often subtle impacts on life history timing, habitat suitability, growth rates, rates of infection, mortality from disease and toxic chemicals, and increased exposure to both native and non-native aquatic predators better adapted to altered water temperatures.
Effects of hydroelectric project operations on the natural temperature regime of riverine sites may sometimes be related to changes in riparian shading due to tree clearing for roads, power lines,and other facilities. However, the primary effects on temperature are related to alterations in water surface area, depth, and velocity due to water diversions into or out of the stream corridor, including reservoir impoundments, and conveyance through pipelines or penstocks. Changes in the water prism along a stream reach influence the balance of heat flux into (e.g., solar radiation, air convection, ground conduction) and out of (e.g., nighttime re-radiation, evaporative cooling, and ground conduction) the reach. These effects are even more pronounced at reservoir sites, where the ratio of water surface area to reservoir volume is much smaller than that found in riverine sites, which alters the rates and balance of heat exchange with the surrounding environment. Methods to assess these effects are described below.
The following reference is recommended for additional information on instream water temperature:
Poole, G. C., and C. H. Berman. 2001. An ecological perspective on in-stream temperature:natural heat dynamics and mechanisms of human-caused thermal degradation. Environmental Management 27:787-802.
Depending on the spatial distribution of local effects (e.g., due to a point discharge, reservoir, etc.) or more widely across a watershed scale, several temperature monitoring techniques may be employed. Digital temperature data loggers (thermographs) are among the most widespread instruments in use for continuous monitoring of water temperatures in aquatic ecosystems. Thermographs are generally mounted securely in a representative location (e.g., pool, riffle, etc.) for one or more seasons, and data are regularly downloaded. A number of considerations in deploying and collecting temperature data are important, including number of times temperature is monitored, interval of collection, and location of sites (Dunham et al. 2005).
In addition to direct temperature monitoring, recent remote sensing techniques such as forward looking infrared radiometry (FLIR) allow for the collection of spatially continuous surface temperature profiles over large areas at one time (i.e. synoptic sampling). This could be used both as a diagnostic tool to compare affected areas with reference areas, locate particular stream reaches with temperature in excess of established criteria or discontinuities due to dams, cooling water discharges, hyporheic exchanges, or hot springs. This information could be used to further develop a continuous monitoring program to characterize and ameliorate any identified impacts. This method has been applied throughout the United States including at the Lake Chelan Hydroelectric Project (FERC Project No. 637) on the Chelan River, Washington; within the Yadkin Pee-Dee River Hydroelectric Project (FERC Project No. 2206) study area, North Carolina; and at the Norway and Oakdale Hydroelectric Project (FERC Project Nos. UL00-2, UL00-1) in the Tippecanoe River basin, Indiana.
2.2.1.1 Selected references
Dunham, J., G. Chandler, B. Rieman, and D. Martin. 2005. Measuring stream temperature with digital data loggers: a user’s guide. General Technical Report RMRSGTR-150WWW. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fort Collins, Colorado.
Torgersen, C. E., R. N. Faux, B. A. McIntosh, N. J. Poage, and D. J. Norton. 2001. Airborne thermal remote sensing for water temperature assessment in rivers and streams. Remote Sensing of Environment 76: 386-398.
Information gathered during water temperature monitoring can be used to model temperature effects of dams, and to develop strategies to ameliorate temperature impacts related to project operations. Stream temperature modeling can be accomplished on both reach and basin scales. The particular choice of modeling scale is most often determined by the question at hand which, for example, could range from temperature effects related to road crossings to basin-wide issues such as forest management practices.
Reach-scale models are often used to examine localized phenomena such as alterations in the riparian canopy (e.g., roads, power lines, etc.) or cold and warm water discharges. Commonly used physical models include SSTEMP (Bartholow 2002), HeatSource (Boyd and Kasper 2003), and others that were developed from channel and valley geometry, shade estimates, hydrology, and meteorology (Brown 1969). Although they may be calibrated accurately to a known temperature record, reach-based models are sometimes unable to adequately account for large changes in model inputs outside of the validated calibration ranges, or account for other effects such as tributary mixing and hyporheic exchanges.
Basin-scale models are more often used to examine land use effects on temperature regimes, but may be applied to evaluate effects of distributed project features on downstream temperatures. Common network-based models, including SNTEMP (Theurer et al. 1984), HSPF (Bicknell et al. 1997), QUAL2k (Chapra et al 2005), and others evaluate entire watersheds by calculating the temperature of individual reaches and then hydraulically routing the heat downstream. Because network-based models require substantial field-measured input data to operate and frequently do not explicitly evaluate uncertainty, more sophisticated landscape Geographic Information System (GIS)-based models such as BasinTemp (Allen et al. 2005) have been employed over larger watersheds where temperature data may be sparse.
Water temperature modeling approaches have been applied at numerous hydroelectric facilities throughout the United States including at the Cooper Lake Hydroelectric Project (FERC Project No. 2170) on Cooper Creek, Alaska; Box Canyon Hydroelectric Project (FERC Project No. 2042) on the Box Canyon Reservoir, Washington; and at the Lake Chelan Hydroelectric Project (FERC Project No. 637) on the Chelan River, Washington.
2.2.2.1 Selected references
Allen, D., W. Dietrich, P. Baker, F. Ligon, and B. Orr. 2005. Development of a mechanistically based, basin-scale stream temperature model: applications to cumulative effects modeling. Technical Report PSW-GTR-194. USDA Forest Service.
Bicknell, B. R., J. C. Imhoff, J. L. Kittle, Jr. A. S. Donigian, and R. C. Johanson. 1997. Hydrological Simulation Program, FORTRAN: User's manual for Version 11. Report EPA/600/R-97/080. U. S. Environmental Protection Agency, National Exposure Research Laboratory.
Boyd, M., and B. Kasper. 2003. Analytical methods for dynamic open channel heat and mass transfer: methodology for heat source model. Version 7.0. Watershed Sciences, Portland, Oregon.
Brown, G. W. 1969. Predicting temperatures of small streams. Water Resources Research 5: 68-75.
Chapra, S. C., G. J. Pelletier, and H. Tao. 2005. QUAL2K: a modeling framework for simulating river and stream water quality. Version 2.02: documentation and users manual. Civil and Environmental Engineering Department, Tufts University, Medford, Maryland.
Sinokrot, B. A., and H. G. Stefan. 1993. Stream temperature dynamics: measurements and modeling. Water Resources Research 29: 2299-2312.
Theurer, F. D., K. A. Voos, and W. J. Miller. 1984. Instream water temperature model. Instream Flow Information Paper No. 16, FWS/OBS-84/15. U. S. Fish and Wildlife Service, Western Energy and Land Use Team, Washington, D. C.
Additional information on water temperature modeling >>
Lakes and reservoirs have distinct structures that arise by the basin geology, morphometry, hydrology, and meteorology that affect the distribution of light, heat, and water circulation and exchange. Changes in instream water quality are inevitable when free-flowing water becomes impounded as deeper, still waters within project reservoirs, and then back to riverine environments downstream of sluice gates, spillways, and generator tailraces. If the water supply was artificially impounded as part of the original hydroelectric project development, water and power demands along with the need for flood control very often dictate the regulation and control of stream flow. Variations in flows and the large size and variations in reservoir storage volumes often disrupt natural processes that would occur if water were not impounded, or that occur in the present day upstream and downstream of the impoundment.
In general, the water column in most reservoirs has a characteristic temperature structure that is independent of the size of the basin. In summer, thermal stratification occurs, with warmer water overlying colder and denser water, much like summertime thermal stratification found in many temperate lakes (Figure 1). Depending on the flow and temperature of water entering the reservoir and the particular configuration of the reservoir inlet and outlet structures, this vertical zonation very often prevents water exchanges between warmer surface waters (epilimnion) and bottom waters (hypolimnion). Depending on the overall aquatic and upland productivity of the system, this zonation may result in hypolimnetic oxygen depletion due to the decay of natural organic matter, with subsequent increases in metals, and increased rates of nutrient exchange at the sediment water interface. Releases of this impounded water can effect downstream populations of fish and other aquatic organisms due to decreased levels of dissolved oxygen; increased levels of metals, nutrients, and turbidity; or altered temperatures.
Various approaches for evaluating reservoir temperature and chemical structure are used by researchers, the most common of which are discussed below, including lake and reservoir water sampling, sediment sampling, and bioindicator monitoring.
The following references are recommended for additional information on reservoir temperature and chemical structure:
Horne, A. J. and C. R. Goldman 1994. Limnology. McGraw-Hill. New York.
Wetzel, R. G. 2001. Limnology: lake and river ecosystems. Academic Press, San Diego, California.
Vertical water samples from lakes and reservoirs can be used to determine the characteristic structures of lakes in summer and winter and to determine important transition periods such as fall overturn, when bottom waters are rapidly exchanged with surface waters. To represent reservoir water quality and structure, in-situ profiles of physical water quality (e.g., temperature, dissolved oxygen [DO], conductivity, pH, turbidity) are collected from the reservoir surface to near the bottom of the deeper portions of each reservoir using available multiple parameter instruments (e.g., HydroLab, YSI). Depending on the resulting temperature and dissolved oxygen profiles and the current and past land uses in the basin, more intensive grab sampling and analytical monitoring of nutrients and toxic substances may also be conducted.
This method has been applied at numerous facilities including at the Niagara Power Project (FERC Project No. 2216) in Lewiston Reservoir, New York; at the Packwood Lake Hydroelectric Project (FERC Project No. 2244) in Packwood Lake, Washington; and at the Klamath Hydroelectric Project (FERC Project No. 2082) in the J. C. Boyle Reservoir, Oregon.
2.3.1.1 Selected references
Horne, A. J. and C. R. Goldman 1994. Limnology. McGraw-Hill. New York.
Wetzel, R.G., and Likens, G.E. 2000. Limnological analyses. Third edition. Springer, New York.
While hydroelectric project operation and maintenance is generally not associated with the discharge of sediment-bound contaminants, changes in the water column mixing discussed above coupled with the high sediment trapping efficiency of reservoirs can lead to increased concentrations of many toxic substances. Synthetic organic chemicals containing chlorine, including carbon tetrachloride and trichloroethylene, were available commercially by 1925, and the insecticidal properties of these compounds (e.g., dichloro-diphenyl-trichloroethane [DDT]) were recognized around 1940. Because of their persistence in the environment, the legacy of these and more recently developed compounds must be considered in any sampling program.
Depending on past and present land uses in both reservoirs and upstream areas, transported and deposited sediments act as sinks for contaminants in the reservoirs due to their high adsorption capacity, and in agricultural and industrial areas, may contain excess nutrients, bacteria, oil and grease, heavy metals, herbicides, pesticides, polychlorinated biphenyls (PCBs), and other materials.
If water quality samples identify analytical parameters above applicable water quality criteria or there is a known past or present activity in the watershed that may contribute to sediment contamination, a number of sediment sampling techniques are available to determine the extent and potential sources of the impairment. Because some toxic inorganic substances and organic contaminants associated with the sediments can also be bioconcentrated by the aquatic organisms present in reservoirs, site-specific bioindicators are often used to detect the presence of materials that may not be identified above the detection limits of most analytical water or sediment quality techniques. For example, fish tissue analysis is commonly used to detect the presence of mercury, arsenic, PCBs, and other contaminants. This method has been applied in several reservoirs in New England as part of Maine Department of Environmental Protection's Surface Water Ambient Toxic Monitoring Program; in the Clinch River and Watts Bar Reservoir, Tennessee; and at the Pueblo Reservoir, Colorado.
2.3.2.1 Selected references
Barbour, M. T., J. Gerritsen, B. D. Snyder, and J.B. Stribling. 1999. Rapid bioassessment protocols for use in streams and wadeable rivers: periphyton, benthic macroinvertebrates, and fish. Second edition. EPA 841-B-99-002. U. S. Environmental Protection Agency, Office of Water, Washington, D. C.
EPA (U. S. Environmental Protection Agency). 2000. Guidance for assessing chemical contaminant data for use in fish advisories. Volume 1: Fish sampling and analysis. Third edition. Office of Water, Washington, D. C. EPA 823-B-00-007.
Hilsenhoff, W. L. 1988. Rapid field assessment of organic pollution with a family-level biotic index. Journal of the North American Benthological Society 7: 65-68.
Slotton, D. G., J. E. Reuter, and C. R. Goldman. 1995. Mercury uptake patterns of biota in a seasonally anoxic northern California reservoir. Water, Air, and Soil Pollution, 80: 841-850.
Smith, A. G. 1991. Chlorinated hydrocarbon insecticides. Pages 731-916 in W. J. Hayes, Jr. and E. R. Laws Jr., editors. Handbook of pesticide toxicology. Academic Press, San Diego, California.
USACE (U.S. Army Corps of Engineers). 1997. Hydrologic engineering requirements for reservoirs. Washington, D. C. EM 1110-2-1420, CECW-EH-Y.
Hydroelectric projects have the potential to alter the flow of nutrients (e.g., phosphorous in sediments, algal bound nitrogen) and energy flow in river systems. Because of the long hydraulic residence times and high particle trapping efficiency of reservoirs, they often provide ideal conditions necessary for algal blooms (i.e., excess nutrients and sunlight, no flushing of algae growing in suspension) with subsequent reservoir eutrophication (water pollution caused by these excess plant nutrients) becoming a common problem associated with ongoing hydroelectric operations.
The trophic state of a lake or reservoir is based on overall system productivity and is a function of physical features (e.g., latitude and elevation as they affect sunlight and air temperatures; ratio of watershed to waterbody areas; reservoir depth; or hydraulic residence time), chemical features (e.g., nutrients, oxygen), and biological responses (e.g., primary productivity, zooplankton and fish assemblage food webs and biomass). In low-oxygen conditions of many reservoir sediments, the adsorption bond between phosphorus and sediment particles becomes unstable and often results in the transformation and release of the adsorbed phosphorus into orthophosphate (i.e. previously precipitated phosphorous becomes dissolved into the water column again). Phosphorous is often a limiting nutrient and when orthophosphate it allows an increase it algal productivity. The decomposition following algal blooms absorb oxygen out of the water, leading to an oxygen deficit. Seasonal changes in reservoir stratification are often accompanied by periods with higher and lower amounts of oxygen, leading to periods of adsorption and desorption of phosphorus, or "internal cycling," which can lead to large algal blooms during spring and fall when large exchanges of surface and bottom waters occur.
Although the most common nutrient limiting the primary production in freshwater is dissolved phosphates, nitrogen compounds can limit production in alpine and arid climates where many hydroelectric developments are situated and where watershed productivity and soil nitrogen retention is low. This has implications for both the influence of air deposition of nitrogen compounds from atmospheric sources, and also of fish passage on nitrogen arriving in river systems with migratory salmonid populations.
The following references are recommended for additional information on eutrophication:
Horne, A., and C. Goldman. 1994. Limnology. McGraw-Hill, New York.
Triska, F. J., J. R. Sedell, and S. V. Gregory. 1982. Coniferous forest streams. Pages 292-332 in R. L. Edmonds, editor. Analysis of coniferous forest ecosystems in the western United States. Hutchinson Ross, Stroudsburg, Pennsylvania.
USACE (U.S. Army Corps of Engineers). 1997. Hydrologic engineering requirements for reservoirs. Washington, D. C. EM 1110-2-1420, CECW-EH-Y.
Vollenweider, R. A., and J. Kerekes. 1982. Eutrophication of waters: Monitoring, assessment and control. OECD Cooperative programme on monitoring of inland waters (Eutrophication control),Environment Directorate, OECD, Paris.
Wetzel, R. G. 2001. Limnology: lake and river ecosystems. Third edition. Academic Press, San Diego, California.
Various approaches for evaluating nutrient exchange and reservoir eutrophication are used by researchers, a few of which are discussed below.
To assess the relative productivity of hydroelectric project reservoirs as compared with pristine sites, one commonly used tool is the trophic state index (TSI). TSI values are based on the relationship between nutrients (as measured by total phosphorus), algal biomass (chlorophyll-a), and water clarity (Secchi disk depths). A regular reservoir sampling program (e.g., quarterly, monthly) may be used to develop background data to determine the TSI. In addition to direct reporting of the TSI, comparisons to regional and national reference values may be developed to assess the severity of any identified impairment of water quality.
This method has been applied in numerous reservoirs including those within the Roanoke River Basin as part of the Roanoke River Basinwide Water Quality Management Plan, North Carolina and Virginia; at the Flaming Gorge Reservoir, Utah; and at Webbers Falls Reservoir, Oklahoma.
2.4.1.1 Selected reference
Carlson, R. E. 1977. A trophic state index for lakes. Limnology and Oceanography. 22(2): 36-369.
Stable isotope analysis has increasingly been used to determine trophic relationships in aquatic food webs. In addition to assessing natural or anthropogenic sources of nutrients associated with reservoir eutrophication, stable isotopes can be used to identify subtler food web effects related to the natural flow of nutrients from headwater reaches downstream. For example, in river systems that historically or currently support salmonid populations, the amount of nitrogen arriving in the form of post-spawning carcasses has been hypothesized as a major source of natural productivity to headwater reaches. Because dams often impede or block fish migration routes, stable nitrogen isotope ratios may be used to indicate the relative contribution of food web nitrogen in biota arriving from atmospheric, biotic, or industrial sources. This analysis has also been used to document the historical distribution of anadromous fish, as described in Section 4.0.
2.4.2.1 Selected references
Finlay, J. C., S. Khandwala, and M. E. Power. 2002. Spatial scales of carbon flow in a river food web. Ecology 83:1845-1859.
Gende, S. M., R. T. Edwards, M. F. Willson, and M. S. Wipfli. 2002. Pacific salmon in aquatic and terrestrial ecosystems. BioScience 52: 917-928.
Hobson, K. A. 1999. Tracing origins and migration of wildlife using stable isotopes: a review. Oecologia 120:314-326.
McCutchan, J., W. Lewis, C. Kendall, and C. McGrath. 2003. Variation in trophic shift for stable isotope ratios of carbon, nitrogen, and sulfur. Oikos 102: 378-390.
Post, D. M. 2002. Using stable isotopes to estimate trophic position: models, methods, and assumptions. Ecology 83: 703-718.
Vander Zanden, M. J., and J. B. Rasmussen. 1999. Primary consumer d13C and d15N and the trophic position of aquatic consumers. Ecology 80: 1395-1401.
Vander Zanden, M. J., and J. B. Rasmussen. 2001. Variation in d15N and d13C trophic fractionation: implications for aquatic food web studies. Limnology and Oceanography 46: 2061-2066.
Dissolved gas supersaturation, which is associated with powerhouse discharges due to increasing gas solubility with increasing hydrostatic pressure within hydroelectric project penstocks, received considerable attention in Canada and the United States. Elevated total dissolved gasses (TDG) can lead to a physiological condition known as gas bubble trauma in aquatic biota, which can be harmful or even fatal to aquatic organisms, as demonstrated by a number of significant fish kills in the Columbia and Snake rivers. As TDG rises from saturation to levels above 110-120 percent of saturation, there is a significant driving force of dissolved gasses into body tissues of fish and other organisms, leading to stress and mortality in some cases. Although many fish forage in or otherwise occupy deeper layers where this driving force is lower due to higher hydrostatic pressure, many resident fish use shallow waters to carry out their life cycles. Invertebrates also can develop bubbles in supersaturated water and lose the ability to swim normally, which may result in long term shifts in invertebrate community structure below powerhouse tailraces.
While modern runner and tailrace designs often can reduce the potential for TDG problems, monitoring is generally conducted in systems with hydrostatic head as little as 8 m (25 ft) because of the potential for attaining equilibrium gas concentration in excess of 110% of saturation. Reconnaissance-level surveys may be conducted using barometrically compensated dissolved gas pressure sampling devices (e.g., HydroLab and others) to determine total dissolved gas pressure. Depending on the initial levels found, the need for additional sampling or continuous monitoring during normal project operations may be assessed.
2.5.1.1 Selected references
Fidler, L. E. and S. B. Miller. 1994. British Columbia water quality guidelines for dissolved gas supersaturation. Report to BC Ministry of Environment, Canada Department of Fisheries and Oceans Environment. Aspen Applied Sciences, Ltd., Valemont, B.C.
ISAB (Independent Scientific Advisory Board). 1998. Review of the U.S. Army Corps of Engineers' Capital Construction Program, Part II, B: Dissolved Gas Abatement Program. Prepared for the Northwest Power Planning Council and the National Marine Fisheries Service. Portland, Oregon.
Weitkamp, D. E., and M. Katz. 1980. A review of dissolved gas supersaturation literature. Transactions of the American Fisheries Society 109: 659-702.
The hydrologic regime directly affects the physical and biological attributes of a river system, including sediment transport (Section 3.3), large woody debris (Section 3.6), water temperature (Section 2.2), and aquatic habitat (Section 4.1). Hydroelectric projects often substantially alter the hydrologic regime by
Hydrologic studies are an integral component to a hydroelectric relicensing process. Unregulated and regulated flow records are required to evaluate sediment and large woody debris transport processes that influence changes in sediment storage, channel morphology, and bed surface texture. Hydrographs are important tools when evaluating current aquatic habitat condition, and changes from unimpaired to regulated flow regimes are necessary to quantify a project's past and potential future effects on aquatic habitat. Spill histories from project dams and measurements of flow fluctuations are common components of fisheries studies, including evaluation of aquatic habitat connectivity and fish stranding. Whitewater boating feasibility studies also commonly rely on flow records and spill histories generated from hydrologic studies.
Statistical analyses of discharge records provide metrics for characterizing and assessing changes in flow regimes on an hourly, daily, monthly, and annual basis (e.g., Indicators of hydrologic alteration by Richter et al. [1996], and Range of variability approach by Richter et al. [1997, 1998]). Relevant statistical parameters for related studies vary with study objectives. An aquatic habitat study, for example, may emphasize components of the hydrograph critical to the species being studied (as discussed in Section 4.1.8); while a sediment transport study may focus on annual flow duration curves and flood frequency. Statistical analyses of project-induced changes in hydrology typically include:
An assessment of project-induced changes in hydrology using pre- and post-project flow data should be made from gages with the longest possible period of record.
3.1.1.1 Selected references
Richter, B. D., J. V. Baumgartner, J. Powell, and D. P. Braun. 1996. A method for assessing hydrologic alteration within ecosystems. Conservation Biology 10: 1163-1174.
Richter, B. D., J. V. Baumgartner, R. Wigington, and D. P. Braun. 1997. How much water does a river need? Freshwater Biology 37: 231-249.
Richter, B. D., J. V. Baumgartner, and J. Powell. 1998. A spatial assessment of hydrologic alteration within a river network. Regulated Rivers: Research and Management 14: 329-340.
Dividing the hydrologic record for streams into water year types allows for characterization of important flow parameters during wet, normal, and dry periods. Characterizing the flow regime during different climate cycles can have significant ramifications for aquatic and terrestrial biological evaluations as well as for assessing sediment supply and transport during flood and drought periods. The timing (in addition to volume) of hydrologic events can also have important biological implications. For example, a summer drought may have a greater or lesser impact on aquatic species depending on whether it was preceded by a wet or dry spring.
Schemes for classifying water year type typically utilize one of three approaches:
The latter two approaches designed for forecasting annual water budgets are typically derived from snow pack measurements and/orUSGS flow records, and the suitability of these approaches for hydro relicensing studies are case specific.
Because the computational methods for determining the water year classification scheme in these latter two approaches varies by region, agency, and/or hydro facility and may be pre-determined prior to the onset of hydrorelicensing studies, these methods are not covered in detail here.
When utilizing unregulated USGS gage records to develop a water year classification scheme, annual runoff volumes are typically classified into either a 3-tier scheme (i.e., wet, normal, anddry) or a 5-tier scheme (i.e. wet, above normal, normal, below normal, and dry). One approachfor determining the statistical break points for a 3-tier classification system is to utilize the mean and standard deviation of the annual runoff volumes for the period of record. Under this approach, normal water years are defined as those years in which the annual runoff volume is within one standard deviation of the mean annual runoff volume for the period of record, wet water years are defined as those years in which the annual runoff volume is greater than or equal to one standard deviation above the mean annual runoff volume for the period of record, and dry water years are defined as those years in which the annual runoff volume is less than or equal to one standard deviation below the mean. Another approach to determining the statistical breakpoints for a water year classification system is to rank the annual runoff volumes and divide the data into equally sized classes, such that in a 3-tier system each class contains 33.3% of the records, and in a 5-tier system each class contains 20% of the annual runoff records.
Characterizing the frequency, magnitude, and duration of reservoir spills for a project facility is often necessary to assess the biological effects of spillgate operation and the rapid change in discharge downstream of a dam during spills. Four primary sources of information may be used to develop spill histories:
The preferable approach is to analyze reservoir elevation and spillgate opening records, since these are direct measurements from which spill magnitudes and durations can be calculated. In cases where reservoir elevation and spillgate data are unavailable, alternative approaches can be used to evaluate spill history. Where projects have limited storage capacity, power generation records may be used to determine spills. When generation is offline, flow must be conveyed through bypass valves or over a spillway rather than through turbines. In these cases, generation records can be used in combination with downstream discharge records to characterize spill statistics. However, in some cases flows may be passed through devices for which there are no generation or gate records (e.g., low-flow pipes, sluice gates).
A project's operations model can be used to develop or extend the spill histories for periods in which the model results exhibit good agreement between predicted spills and documented spills (typically telemetric data). An operations model uses a water balance approach of reservoir operations that accounts for flow through the project reservoirs, tunnels, and powerhouse system. A typical operations model includes long-term USGS records, estimates of local inflow from bypass reaches and contributing areas downstream of USGS gages, and a power generation pattern for the project powerhouses developed from recorded generation data. Reservoir spills and magnitudes are typically produced as part of the output from a project's operational model.
3.1.3.1 Selected reference
Stillwater Sciences. 2006. Hydrologic regimes at the Carmen-Smith Hydroelectric Project, upper McKenzie River basin, Oregon. Final report. Prepared by Stillwater Sciences, Arcata, California for Eugene Water & Electric Board, Eugene, Oregon.
Characterizing flow fluctuations (change in water surface stage) induced by project operations can be particularly relevant for assessing aquatic biological effects such as fish stranding, as discussed in Section 4.2. In addition, if stream channels are composed of unconsolidated material and flow fluctuations are severe, the fluctuations can induce bank instability and erosion. Operational data for characterizing flow fluctuations commonly includes records of reservoir elevation, power generation from the project powerhouses, spillgate and bypass valve openings, inflow from tributaries or other sources, and stage heights and discharges downstream of project dams. Additional, temporary water surface loggers are often deployed in order to monitor flow fluctuations at multiple locations and quantify the downstream extent and magnitude of flow fluctuations.
Where possible, long-term flow records from USGS gage data combined with spill and flow diversion records from project facilities can be used to create synthetic long-term regulated and unregulated flow records. However, study reaches are often located in ungaged basins and the USGS gage period of record often does not encompass the complete period of interest (i.e., either the unregulated or regulated periods are not part of the period of record). Therefore, it is often necessary to construct synthetic long-term flow records for regulated and unregulated periods of record in ungaged basins. A common approach to constructing synthetic flow records is to install temporary discharge monitoring stations and correlate these flow records to discharge records from nearby USGS gaging stations. When temporary discharge monitoring stations are not installed, a combination of proration (drainage area relationship between the point of interest and the drainage area of a nearby USGS gaging station) and water budget techniques can be used to construct a synthetic discharge record. Proration techniques between ungaged basins with few or no discharge records and gaged basins with long-term discharge records are appropriate as long as the correlated sites drain similar geologic/geomorphic terrain with similar climate (temperature and precipitation) and land use patterns.
3.1.5.1 Selected reference
Tague, C., and G. E. Grant. 2004. A geological framework for interpreting the low-flow regimes of Cascade streams, Willamette River basin, Oregon. Water Resources Research 40: doi 10.1029/2003WR002629.
Sediment dynamics exert important controls on channel morphology and texture that affect habitat quantity and quality for aquatic and riparian species. Aquatic habitat attributes such as spawning gravel availability and the amount of fine sediment in the channel bed are determined by the size distribution and rate of sediment input and by the capacity of stream channels to store and transport sediment. Sediment transport and storage characteristics control the average time required for sediment of various sizes to be routed through the channel network, influencing the sensitivity of channels to disturbances.
Drainage basin geology and geomorphology often control the volume and size distribution of sediment supply, longitudinal pattern of sediment input, and project effects on channel conditions. The preferred approach for characterizing sediment supply depends on the geologic setting and availability of existing information, including
More than one approach may be required to corroborate results.
The following references are recommended for additional information on sediment supply approaches:
Grant, G. E., J. C. Schmidt, and S. L. Lewis. 2003. A geological framework for interpreting downstream effects of dams on rivers. Pages 209-225 in J. E. O'Connor and G. E. Grant, editors. A peculiar river: geology, geomorphology, and hydrology of the Deschutes River, Oregon. Water Science and Application Series No. 7. American Geophysical Union, Washington, D. C.
Petts, G. E. 1979. Complex response of river channel morphology subsequent to reservoir construction. Progress in Physical Geography 3: 329-362.
Williams, G. P., and M. G. Wolman. 1984. Downstream effects of dams on alluvial rivers. Geological Survey Professional Paper 1286. U. S. Geological Survey, Washington, D. C.
Chien, N. 1985. Changes in river regimes after the construction of upstream reservoirs. Earth Surface Processes and Landforms 10: 143-159.
Collier, M., R. H. Webb, and J. C. Schmidt. 1996. Dams and rivers: a primer on the downstream effects of dams. Circular No. 1126. U. S. Geological Survey.
Sediment flux (suspended load or bedload discharge per unit time), estimated from measurements of sediment load in mainstem or tributary channels, is arguably the most reliable metric for evaluating sediment supply to project reservoirs and project-affected reaches. In addition to providing estimates of sediment supply, measured bedload and suspended load flux rates can be used to estimate coarse-to-total load ratios. Bedload sampling technologies include instream installations (e.g., pit traps, net-frame samplers, and detention basins or weir ponds), portable devices (pressure difference samplers, bedload collectors, tracer particles [Figure 2], and scour chains [Figure 3] or cores), and surrogate technologies (acoustic Doppler, hydrophones, gravel impact sensors, magnetic tracers, and topographic differencing). Suspended sediment sampling technologies include single and multi-frequency acoustics, laser defraction, optical sediment flux, digital image analysis, pressure differential, and bulk optics.
The usefulness of existing sediment gaging records for characterizing the longitudinal pattern of sediment supply and extrapolating flux rates to other areas depends on the length of time sediment flux has been monitored and the distribution of monitoring sites relative to geologic terrains, tributaries, and other areas important to sediment production. Correlation of long-term sediment gaging records to flow gaging records is necessary to characterize variability in flux rates over different water year types, especially when projects are located in geomorphic settings characterized by stochastic erosion processes that deliver sediment to channels and mobilize stored channel sediment during large, infrequent triggering events (e.g., large storms, fires, earthquakes, and volcanic eruptions). Short-term gaging records can be correlated to other longterm sediment gaging records if sediment supply is controlled by similar geology, climate, hydrology, and land use.
3.2.1.1 Selected references
Edwards, T. K., and G. D. Glysson. 1999. Field methods for measurement of fluvial sediment. U. S. Geological Survey, Techniques of Water-Resources Investigations, Book 3, Chapter C2.
Gray, R. D., editor. 2003. Proceedings of the Federal Interagency Sediment Monitoring Instrument and Analysis Research Workshop. 9-11 September. Flagstaff, Arizona.
Reservoir sedimentation reflects sediment yield from source areas and can be used to estimate average annual unit-area sediment yield. The volume of sediment accumulated in a reservoir since dam construction can be determined using two methods:
Both methods require topographic data for the reservoir basin prior to sediment filling (typically derived from as-built construction drawings) and for current bathymetry. Current bathymetric data are typically useful for a wide range of other resource studies as well as ongoing hydropower operations and maintenance activities. The topographic differencing method has the benefit of describing the spatial distribution of sediment thickness (Figure 4), potentially useful information when evaluating relative sediment yield from geologically and/or geomorphically distinct reservoir source areas (e.g., two rivers flowing in from different geomorphic terrains).
Once the volume of sediment accumulated in a reservoir is determined, the annual unit-area sediment yield to a reservoir can be calculated using the following procedure:
Coring reservoir deposits is one useful approach for determining parameters that otherwise must be estimated from literature values, including sediment density and grain size distribution, organic matter content, age based on isotope geochronometers (i.e., 137Cs, 7Be, and 210Pb), and correlation of event stratigraphy to floods in the hydrologic record. A coring campaign designed to characterize the age and volume-averaged grain size distribution of reservoir sediment requires an array of sample sites extending the length of a reservoir's longitudinal axis. If the volume averaged grain size distribution of reservoir sediment is determined through coring and laboratory analysis, annual yields can be partitioned by grain size.
3.2.2.1 Advantages and disadvantages of approach
Measuring reservoir sedimentation to examine sediment supply has advantages and disadvantages relative to the other approaches evaluated, as discussed below:
Advantages:
Disadvantages:
3.2.2.2 Selected references
Ambers, R. 2001. Using the sediment record in a western Oregon flood-control reservoir to assess the influence of storm history and logging on sediment yield. Journal of Hydrology 244: 181-200.
Morris, G. L., and J. Fan. 1998. Reservoir sedimentation handbook: design and management of dams, reservoirs, and watersheds for sustainable use. McGraw-Hill, New York.
Snyder, N. P., D. M. Rubin, C. N. Alpers, J. R. Childs, J. A. Curtis, L. E. Flint, and S. A. Wright. 2004. Estimating accumulation rates and physical properties of sediment behind a dam: Englebright Lake, Yuba River, northern California. Water Resource Research 40.
Stillwater Sciences. 2006. Sediment budget for the Carmen-Smith Hydroelectric Project area, upper McKenzie River basin, Oregon. Final report. Prepared by Stillwater Sciences, Arcata, California for Eugene Water & Electric Board, Eugene, Oregon.
Long-term monitoring of sediment flux and field inventory of erosion features required to completely and accurately describe sediment supply is often limited by lack of existing information, the scope of hydroelectric project effects, and the short time-frame encompassed by relicensing studies. A rapid approach to characterizing sediment supply involves extrapolation of geomorphic processes and rates based on terrain modeling, published process rates, analysis of historical aerial photographs, and direct field observations. This approach is commonly employed in source analyses for sediment Total Maximum Daily Load (TMDL) studies.
The rapid approach typically involves the following procedure:
Extrapolation of geomorphic processes and rates to terrains is well-suited where total production and storage estimates in reservoir source areas can be calibrated to reservoir sedimentation rates.
3.2.3.1 Advantages and disadvantages of approach
An extrapolation of sediment supply based on geomorphic processes and rates has advantages and disadvantages relative to the other approaches evaluated, as discussed below:
Advantages:
Disadvantages:
3.2.3.2 Selected references
Reid, L. M., and T. Dunne. 1996. Rapid evaluation of sediment budgets. Catena Verlag, GMBH, Reiskirchen, Germany.
EPA (U. S. Environmental Protection Agency). 2006. Examples of approved sediment TMDLs
Stillwater Sciences. 2006. Sediment budget for the Carmen-Smith Hydroelectric Project area, upper McKenzie River basin, Oregon. Final report. Prepared by Stillwater Sciences, Arcata, California for Eugene Water & Electric Board, Eugene, Oregon.
Local sediment sources associated with project facilities should be quantified to determine if they individually and collectively contribute significant amounts of sediment to project-affected stream reaches. Local sediment sources may include erosion features in the vicinity of project dams, spillways, powerhouses, penstocks and canals, project roads and trails, transmission line corridors, and reservoir shorelines (shoreline protection is discussed in Section 8.2). Sequential aerial photography, interviews with operations staff, and field surveys are typically used to map sediment sources and differentiate natural from anthropogenic sediment sources. A field inspection of major project-related sediment sources should be conducted to estimate delivery to water bodies. The field inspection should consist of assessment of the erosion processes and activity level, measurements of each major erosion feature (length, width, and depth), estimation of the grain size distribution of the eroding material, and estimation of sediment delivery to water bodies. The significance of each project-related sediment source should be evaluated based on the relative sediment volumes produced and delivered, the relative sensitivity of channels receiving sediment, and the likelihood of continued sediment production.
A coarse-level analysis of channel morphology is commonly conducted for hydroelectric project relicensings to examine historical changes and identify locations for intensive study. Coarse-level analyses utilize historical aerial photographs, digital elevation models (DEM), digital orthophotography, and previous studies on channel geomorphology. A coarse-level analysis typically involves assessment of channel confinement, channel slope, channel sinuosity, sediment source area, presence of alluvial sediment (gravel bars), potential hillslope sediment source areas, and the distribution of side channels.
Based on the coarse-level analysis, intensive sites are selected for detailed geomorphic field studies designed to investigate channel morphology, grain size distributions of channel bed surface and subsurface material, and bed mobility. The general locations of intensive study sites are designed to characterize reaches potentially affected by project operations and to identify key geomorphic areas responsible for significant sediment supply and transport.
Within the general reach locations, intensive study sites are typically located in response reaches most likely to exhibit effects from changes in hydrology, sediment supply, or large woody debris (LWD) loading. Additional criteria that may be used to evaluate the suitability of response reaches includes applicability for sediment transport modeling, minimal direct input of sediment sources to the reach (e.g., severe bank erosion or shallow landsliding) that may locally control channel morphology or bed texture, and minimal localized land use impacts (e.g., riparian timber harvest, channel constrictions due to road construction or crossings, and artificial channel hardening from rip-rapping bank material).
Surveys at intensive study sites commonly involve measuring a longitudinal profile of the channel bed along the thalweg and water surface, sediment facies mapping, three or more cross-sections extending onto the floodplain and to the adjacent hillslope toes where feasible, pebble counts conducted at cross-sections to estimate channel roughness and calibrate facies mapping estimates, coarse particle embeddedness and estimation or measurement of armoring ratio, and bulk sampling of surface and subsurface material located in mobile sediment patches.
3.3.1.1 Advantages and disadvantages of approach
Characterizing channel morphology and bed surface texture to measure sediment transport and channel condition has advantages and disadvantages relative to the other approaches evaluated, as discussed below:
Advantages:
Disadvantages:
3.3.1.2 Selected references
Buffington, J. M., and D. R. Montgomery. 1999. A procedure for classifying textural facies in gravel-bed rivers. Water Resources Research 35: 1903-1914.
Bunte, K., and S. R. Abt. 2001. Sampling surface and subsurface particle-size distributions in wadable gravel- and cobble-bed streams for analyses in sediment transport, hydraulics, and streambed monitoring. General Technical Report No. RMRS-GTR-74. USDA Forest Service, Fort Collins, Colorado.
Montgomery, D. R., and J. M. Buffington. 1997. Channel-reach morphology in mountain drainage basins. Geological Society of America Bulletin 109: 596-611.
Montgomery, D. R., and J. M. Buffington. 1998. Channel processes, classification, and response. Pages 13-42 in R. J. Naiman and R. E. Bilby, editors. River ecology and management. Springer-Verlag, New York.
Bedload transport creates and modifies bedform topography, controls sediment storage, affects surface texture through selective transport and abrasion, influences channel migration, and directly influences aquatic habitat. The flux rate of coarse material is an important component of sediment mass balance within a regulated reach. Higher bedload transport capacity can lead to greater potential geomorphic impacts of reduced coarse sediment supply.
Bedload transport is typically modeled and calibrated with field studies at intensive study sites to estimate surface-based dimensionless Shield stress, critical discharges to mobilize the channel bed, coarse (> 2 mm) bedload transport capacity, and bedload grain size distributions. Model input parameters commonly include channel cross-section data, water surface slope, grain size (channel roughness) data of either the channel surface substrate or the bedload supply, and annual flow duration curves of the current and reference flow regimes. Model output parameters commonly include Shields stress versus discharge rating curves, average annual coarse bedload transport capacity, and grain size distributions of either the bedload supply or channel surface (depending on whether the input parameter was surface or bedload supply grain size). Long-term synthetic hydrologic flow records representing current and reference conditions may be used to generate flow duration curves for modeling bedload transport capacity. To calibrate the reference Shields stress used for sediment transport modeling, marked tracer rocks with grain size approximately equal to the local surface D50 and D84 may be placed at each cross-section to identify thresholds of bed mobility (Figure 2). Tracer rocks are generally placed in a line along previously surveyed cross-sections and monitored after high flow events.
3.3.2.1 Advantages and disadvantages of approach
Modeling bedload transport to measure sediment transport and channel condition has advantages and disadvantages relative to the other approaches evaluated, as discussed below:
Advantages:
Disadvantages:
3.3.2.2 Selected references
Buffington, J. M., and D. R. Montgomery. 1997. A systematic analysis of eight decades of incipient motion studies, with special reference to gravel-bed rivers. Water Resources Research 33: 1355-1380.
Mueller, E. R., J. Pitlick, and J. M. Nelson. 2005. Variation in the reference Shields stress for bed load transport in gravel-bed streams and rivers. Water Resources Research 41: W04006, doi: 10.1029/2004WR003692.
In regulated reaches with abundant supply of fine sediment, decreased peak flow magnitude and/or frequency may increase fine sediment accumulation in pools and in gravel interstices, affecting the quality of stream habitat for fish and other aquatic species. Fine sediment (< 2 mm) accumulation in project-affected reaches (e.g., bypass reaches) can be evaluated by
The V* technique is applicable in reaches with pool-riffle morphology, stable banks, channel gradient less than 5%, and wadable pools. Selected pools must have a definable riffle crest (a pool's hydraulic control and usually the shallowest place at the downstream end of a pool), which excludes pools formed by LWD or boulder dams. In certain cases, a modified V* approach that allows for a greater number of pools to be sampled over a given time period, may be more advantageous to complete the study's objectives. Examples of modified V* methodologies include Stillwater Sciences' streamlined V* (Stillwater Sciences 2006) and S* developed by the Sierra National Forest (USDA Forest Service 1997). Both of these simplified methodologies have shown good correlation with the full V* method of Hilton and Lisle (1993) where both methods are used to characterize the same pool.
3.3.3.1 Advantages and disadvantages of approach
Measuring fine sediment accumulation with the V* method to investigate sediment transport and channel condition has advantages and disadvantages relative to the other approaches evaluated, as discussed below:
Advantages:
Disadvantages:
3.3.3.2 Selected references
Hilton, S., and T. E. Lisle. 1993. Measuring the fraction of pool volume filled with fine sediment. Research Note PSW-RN-414. USDA Forest Service, Pacific Southwest Research Station, Berkeley, California.
Stillwater Sciences. 2006. Fluvial geomorphic processes and channel morphology at the Carmen-Smith Hydroelectric Project area, upper McKenzie River Basin, Oregon. Final report. Prepared by Stillwater Sciences, Arcata, California for Eugene Water & Electric Board, Eugene, Oregon.
USDA Forest Service. 1997. A reconnaissance level indicator of pool fine sediment. Sierra Nevada Forest, Kings River Ranger District, California. Unpublished report.
Project effects on LWD loading, sediment supply, active channel storage, and peak flows may reduce connectivity to side channels, as well as their extent and stability. Reduced peak flow magnitude and/or frequency may also impact the functionality of side channels by reducing access to flow. Methods for evaluating project effects on the distribution, frequency, and length of side channels includes analysis of an aerial photographic time series and field inventories of side channels during low flow. Field inventories may include evaluation of mechanisms of side channel formation (e.g., LWD, channel and/or valley morphologic controls, or sediment deposition), vegetation age on the island bars or terraces between the side channel and main channel, stability of the side channels, and connectivity with the main channel. At the inlet and outlet controls (minimum elevation for surface water from the main channel to connect with the side channel) of the side channels, differential leveling may be used to survey the local water surface and thalweg elevations of the main and side channels to assess topographic controls on surface water flow connectivity with the main channel. Cross-sections and channel roughness data at side channel inlets can also be surveyed as input parameters for water surface modeling aimed at estimating stage-discharge thresholds for surface flow connectivity.
Assessing the distribution of side channels should consider the following:
Channel sediment storage can be altered by sediment trapping in project impoundments, flow regulation, alterations to LWD volume, anthropogenic increases in erosion rates, and other natural events that affect sediment supply and transport. The dynamics of within-reach channel sediment storage, however, is often difficult to assess due to limited historical information, spatial and temporal variability in sediment storage, and uncertainties in sediment activity level and residence time. Changes in stored sediment volume in project-affected reaches may be quantified using several approaches, including reoccupying historical channel cross sections, repeated surveying of channel topography to determine volumetric changes through time, and by assessing the relative activity and response times of sediment in storage based on reservoir theory. Important considerations when planning a study of storage changes include:
Often no historical cross-section or topographic data exist to document initial sediment storage and therefore storage changes. The relative importance of sediment storage can be assessed by estimating the maximum potential for scour and fill at sediment storage sites based on the maximum and minimum surfaces exposed to scour and fill (e.g., typical high water surface elevation and thalweg, respectively). Comparison of potential mass scour and fill estimates to average annual sediment mass balance (supply vs. transport) gives an indication of the potential for average annual storage changes. Marked tracer rocks in gravel bed channels can be monitored over multiple flood events to determine particle transit time, and therefore the age distribution and residence time of stored sediment.
Listed below are advantages and disadvantages of sediment storage approaches:
Advantages:
Disadvantages:
The following references are recommended for additional information on sediment storage approaches:
Gaeuman, D. A., J. C. Schmidt, and P. R. Wilcock. 2003. Evaluation of in-channel gravel storage with morphology-based gravel budgets developed from planimetric data. Journal of Geophysical Research 108 F1 6001: doi:10.1029/2002JF000002.
Hazel, J. E., D. J. Topping, J. C. Schmidt, and M. Kaplinski. 2006. Influence of a dam on fine sediment storage in a canyon river. Journal of Geophysical Research 111 F01025: doi:10.1029/2004JF000193.
Kelsey, H. M., R. Lamberson, and M. A. Madej. 1987. Stochastic model for the long-term transport of stored sediment in a river channel. Water Resource Research 23: 1738-1750.
Lisle, T. E., and M. Church. 2002. Sediment transport-storage relations for degrading, gravel bed channels. Water Resources Research 38: doi:10.1029/2001WR001086.
Wathen, S. J., T. B. Hoey, and A. Werritty. 1997. Quantitative determination of the within reach sediment storage in a small gravel-bed river using transit time and response time. Geomorphology 20: 113-134.
A sediment budget is a useful approach to integrating each of the previously discussed areas of potential hydrogeomorphic effects (hydrology, sediment supply, sediment transport, and sediment storage) into a sediment mass balance perspective that provides a framework for interpreting changes in fluvial geomorphology caused by hydroelectric projects and other land uses. Sediment budgets may be constructed at various scales and to varying levels of detail; ranging from those that incorporate detailed long-term field measurements of sediment supply, transport, and storage processes in a channel reach; to rapid sediment budgets that describe geomorphic processes and rates throughout a drainage basin using the best available information. The methods used to develop a sediment budget depend on the specific goals and objectives of the study, and most of approaches described in previous sections are directly applicable.
The following references are recommended for additional information on sediment budget approaches:
O'Connor, J. E., G. E. Grant, and T. Haluska. 2003. Overview of geology, hydrology, geomorphology, and sediment budget for the Deschutes River basin, Oregon. Pages 7-30 in J. E.
O'Connor and G. E. Grant, editors. A peculiar river: geology, geomorphology, and hydrology of the Deschutes River, Oregon. Water Science and Application Series No. 7. American Geophysical Union, Washington, D. C.
Reid, L. M., and T. Dunne. 1996. Rapid evaluation of sediment budgets. Catena Verlag, GMBH, Reiskirchen, Germany.
Reid, L. M., and T. Dunne. 2003. Sediment budget as an organized framework in fluvial geomorphology. G. M. Kondolf and H. Piegay, editors. Tools in fluvial geomorphology. John Wiley and Sons, Ltd, England.
Stillwater Sciences. 2000. Sediment budget for the North Umpqua River basin. Appendix 2-1 in the North Umpqua cooperative watershed analysis synthesis report. Prepared by Stillwater Sciences, Berkeley, California for PacifiCorp, Portland, Oregon.
Stillwater Sciences. 2006. Sediment budget for the Carmen-Smith Hydroelectric Project area, upper McKenzie River basin, Oregon. Final report. Prepared by Stillwater Sciences, Arcata, California for Eugene Water & Electric Board, Eugene, Oregon.
Large woody debris plays an important role in streams by shaping channel morphology, storing sediment and organic matter, and providing habitat for aquatic species. Woody debris is also important in floodplains and riparian areas by providing cover for terrestrial and riparian-associated species such as small mammals and amphibians. The purposes of a LWD study are often to
The magnitude of project effects on LWD is a function of the amount of LWD trapped in project reservoirs, the potential mobility of that wood, and the distribution of potential depositional zones downstream.
A field inventory of LWD is often conducted in project reaches, and where feasible, in control reaches. Study reaches should be selected using photogrammetry and divide into sub-reaches based on channel confinement and channel gradient. Inventories commonly tally LWD (size criteria vary by geographic locale, relevant tree species, and study objective) that are wholly or partially within the bankfull channel. Detailed data on LWD characterization (e.g., decay class, recruitment mechanisms, association with jam, sediment storage, influence on channel morphology, habitat value) may be colleted for "key pieces" that are of sufficient size or shape to alter channel morphology or for all LWD in a study reach. Mapping LWD locations onto high-resolution, aerial photographs allows for spatial analysis of LWD characteristics.
Comparisons between
can be used to assess project effects on LWD frequency and volume.
Additional data on the volume of LWD removed from reservoir booms or intake structures on annual basis may be available from project operators. On larger reservoirs where expansive "rafts" of LWD may accumulate, aerial photographic analyses can be used to quantify the volume of LWD stored in reservoirs. In some cases where multiple series of aerial photographs are available over a relatively short time period, the annual change in LWD accumulation within a reservoir can be assessed.
Developing conceptual models of LWD dynamics based on geomorphic terrain, channel network position, and degree of project influence provides a framework for assessing project effects. Conceptual models typically characterize the predominate input mechanisms of LWD to a reach, the quantity of LWD stored, LWD residence time, and the primary ecological and geomorphic functions of LWD. As part of the conceptual model, a wood budget may be constructed to estimate LWD accumulation, transport rates, and volumes of LWD removed at project reservoirs on an annual basis. Conceptually, a wood budget uses a mass balance approach to analyze the input, output, depletion, and changes in storage of LWD in a channel network. Simplified wood budgets may be developed to estimate annual LWD recruitment, transport, and delivery rates under reference and current conditions. The wood budgets are intended to characterize long-term LWD dynamics and trends over several-decade time scales. The primary parameters of the wood budgets are LWD inputs from stream channel and reservoir margin hillslopes, and from the fluvial transport of the stream channel inputs to downstream reaches.
Listed below are advantages and disadvantages of large woody debris study approaches:
Advantages:
Disadvantages:
The following references are recommended for additional information on LWD assessment:
Benda, L., D. Miller, J. Sias, R. Bilby, C. Veldhuisen, and T. Dunne. 2003. Wood recruitment processes and wood budgeting. Pages 49-73 in S. V. Gregory, K. L. Boyer and A. M. Gurnell, editors. The ecology and management of wood in world rivers. American Fisheries Society Symposium 37. American Fisheries Society, Bethesda, Maryland.
Benda, L., and J. Sias. 2003. A quantitative framework for evaluating the mass balance of in-stream organic debris. Forest Ecology and Management 172: 1-16.
Lassettre, N. S. 1999. Annotated bibliography on the ecology, management, and physical effects of large woody debris (LWD) in stream ecosystems. Prepared for California Department of Forestry, Sacramento. Department of Landscape Architecture and Environmental Planning, University of California, Berkeley.
Martin, D. J., and L. E. Benda. 2001. Patterns of instream wood recruitment and transport at the watershed scale. Transactions of the American Fisheries Society 130: 940-958.
Montgomery, D. R., and H. Piegay. 2002. Wood in rivers: interactions with channel morphology and processes. Geomorphology 51.
Naiman, R. J., E. V. Balian, K. K. Bartz, R. E. Bilby, and J. J. Latterell. 2002. Dead wood dynamics in stream ecosystems. Pages 23-48 in P. J. Shea, J. W. F. Laudenslayer, B. Valentine, C. P. Weatherspoon and T. E. Lisle, editors. Proceedings of the symposium on the ecology and management of dead wood in western forests. General technical report, PSW-GTR- 181. USDA Forest Service, Pacific Southwest Research Station, Albany, California.
Hydroelectric projects potentially affect many aspects of aquatic communities, as outlined in the Project Effects Matrix (Part I). In addition to affecting aquatic species by disconnecting habitat, hydroelectric projects also potentially impact habitat quality and quantity by altering fluvial processes with disruption of the flow of water, sediment, and woody debris. A variety of approaches are discussed below to evaluate the effects of hydroelectric projects on:
These are not all of the potential effects of hydroelectric projects on aquatic habitats, and the methods to evaluate them by no means cover all the potential approaches that could be used to study the effects. Rather, this discussion focuses on those effects for which a nexus to project effects is most distinct and where approaches to evaluate effects are not necessarily standardized. For example, basic methods to conduct surveys to identify, characterize, and map the distribution of aquatic resources in the project area are not included. Under the relicensing process and associated National Environmental Protection Act (NEPA) and/or Endangered Species Act (ESA) process, information from these types of surveys is used in a risk assessment to determine if the sensitive resources are, or could be, disturbed by the project. Although these surveys are crucial, the approaches they employ are not unique to hydroelectric projects. This report does not discuss methods for basic resource inventories. Instead, it focuses on approaches that are specifically designed to evaluate effects of hydroelectric projects, while still recognizing the importance of general survey data. The following text provides a description of many of the approaches used to describe fish species composition and distribution:
Nielsen, L. A., and D. L. Johnson. 1983. Fisheries techniques. American Fisheries Society, Bethesda, Maryland.
A more recent approach to determining the historic, or pre-project, distribution of aquatic species uses stable isotope tracing (N15). In this approach, similar methods to those described in Section 2.4.2 are used to determine if marine-derived nutrients were ever deposited upstream of current barriers, thus providing evidence of the historical distribution of anadromous species. Although this method has yet to be widely used in hydroelectric relicensing, it has been widely used in other applications, and is currently being applied at the Lake Chelan Hydroelectric Project (FERC Project No. 637) on the Chelan River, Washington.
The quantity, complexity, and quality of riverine habitat available for aquatic species depend to a large extent on the timing, frequency, duration, rate of change, and magnitude of instream flows. These flows vary seasonally and annually, and are affected by flow alterations related to project operations. Results of instream flow studies can be used to evaluate potential beneficial or negative effects of current and proposed instream flow regimes on habitat for life stages of analysis species. Traditionally used approaches to studying instream flows, as well as newly applied approaches, are discussed below, including IFIM and one-dimensional (1D) PHABSIM, two-dimensional (2D) hydrodynamic modeling, habitat criteria mapping, expert habitat mapping, macroinvertebrate community assessments, and flow prescriptions (methods to assess hydroelectric project effects on hydrology, including identifying natural hydrograph components, are discussed above in Section 3.1). These approaches were selected for evaluation because they are commonly used, and/or have been successful at providing relicensing participants with the information needed to select appropriate flows.
Many additional approaches to evaluating instream flows are available, including the following methods evaluated in detail in Annear et al. (2004):
All of the methods listed and discussed are only useful if they are applied to specific and appropriate questions. Many of the disadvantages of these approaches can be avoided by clearly identifying the questions for the project, and applying the methods in a directed way. In addition, these approaches are typically more successful when used in conjunction with other approaches.
Limitations associated with all instream flow approaches include:
4.1.1.1 Selected references
Annear, T., I. Chisholm, H. Beecher, A. Locke, P. Aarrestad, N. Burkhart, C. Coomer, C. Estes, J. Hunt, R. Jacobson, G. Jobsis, J. Kauffman, J. Marshall, K. Mayes, C. Stalnaker, and R. Wentworth. 2004. Instream Flows for Riverine Resource Stewardship, revised edition. Instream Flow Council, Cheyenne, WY.
Arthington, A. H., and M. J. Zalucki. 1998. Comparative evaluation of environmental flow assessment techniques: review of methods. Land and Water Resources Research and Development Corporation, Canberra, Australian Capitol Territory.
EA Engineering, Science, and Technology,. 1986. Instream flow methodologies. Final Report EA-4819, Project 2194-2. Prepared for Electric Power Research Institute by EA Engineering, Lafayette, California.
Jowett, I.G., 1997: Instream flow methods: a comparison of approaches. Regulated Rivers 13. 115-127.
Kondolf, G. M., E. W. Larsen, and J. G. Williams. 2000. Measuring and modeling the hydraulic environment for assessing instream flows. North American Journal of Fisheries Management 20: 1016-1028.
Railsback, S. 2001. Instream flow assessment methods: guidance for assessing instream flow needs in hydropower relicensing. Electric Power Research Institute, Palo Alto, California.
The instream flow incremental methodology (IFIM) and one-dimensional (1D) physical habitat simulation (PHABSIM) modeling are standard approaches to assessing instream flow needs for aquatic species (Figure 5). The first step is to perform a detailed stream or aerial survey, or map habitats, in the study area to determine the extent and distribution of habitat types. Following habitat mapping, individual study reaches and instream flow transect locations are established. Hydraulic and habitat data are collected at each transect using standard techniques employed in instream flow studies. The transect data are then processed through hydraulic simulation submodels within the PHABSIM model, generating simulations of depth and velocity distributions over a broad range of flows. Literature-derived or site-specific habitat suitability criteria (HSC) are applied to the predicted hydraulic parameters to produce functional relationships between flow and aquatic habitat (expressed as weighted usable area, or WUA). Lastly, a habitat time series analysis is performed to integrate WUA results across spatial (reach-long) and temporal (over the hydrologic period of record) scales.
4.1.2.1 Advantages and disadvantages of approach
Use of IFIM and one-dimensional (1D) PHABSIM to assess instream flows has advantages and disadvantages relative to the other approaches evaluated, as discussed below:
Advantages
Disadvantages
4.1.2.2 Site-specific considerations and applicability
Many of the advantages and disadvantages of this approach will depend on site-specific considerations, as discussed below:
4.1.2.3 Selected references
Bovee, K.D., B.L. Lamb, J.M. Bartholow, C.B. Stalnaker, J. Taylor, and J. Henriksen. 1998. Stream Habitat Analysis Using the Instream Flow Incremental Methodology. Fort Collins, CO: U.S. Geological Survey-BRD. Information and Technology Report USGS/BRD/ITR-1998-0004. 130 p.Parasiewicz, P. 2001. MesoHABSIM: a concept for application of instream flow models in river restoration planning. Fisheries 26: 6-13.
Castleberry, D. T., J. J. Cech, Jr., D. C. Erman, D. Hankin, M. Healey, G. M. Kondolf, M. Mangel, M. Mohr, P. B. Moyle, J. Nielsen, T. P. Speed, and J. G. Williams. 1996. Uncertainty and instream flow standards. Fisheries 21: 20-21.
Milhous, R.T. 1998. Application of the principles of IFIM to the analysis of environmental flow needs for substrate maintenance in the Trinity River, northern California. In: Hydroecological Modelling: Research, practice, legislation, and decision-making. Praha, Czech Republic: T.G. Masaryk Water Research Institute. p. 50-52.
Milhous, R. T., D. L. Wegner, and T. Waddle. 1984. User's guide to the Physical Habitat Simulation System (PHABSIM). Instream Flow Information Paper No. 11, FWS/OBS-81/43 Revised. Prepared by Instream Flow and Aquatic Systems Group, U. S. Fish and Wildlife Service, Fort Collins, Colorado and U. S. Bureau of Reclamation, Upper Colorado Region, Salt Lake City, Utah for U. S. Fish and Wildlife Service, Washington, D. C.
Nakamura, S., and T. J. Waddle. 1999. IFIM Nyuumon (Translation of two documents into Japanese: The Instream Flow Incremental Methodology - A Primer for IFIM and Stream Habitat Analysis Using the Instream Flow Incremental Methodology). Tokyo, Japan: Technology Center for Riverfront Development. 197 p.
Railsback, S. 1999. Reducing uncertainties in instream flow studies. Fisheries 24: 24-26.
Stalnaker, C.B. 1998. The Instream Flow Incremental Methodology. In: Hydroecological Modelling: Research, Practice, Legislation and Decision-Making. Prah, Czech Republic: T. G. Masaryk Water Research Institute. p. 9-11.
Stalnaker, C.B., B.L. Lamb, J. Henriksen, K. Bovee, and J. Bartholow. 1995. The Instream Flow Incremental Methodology: A Primer for IFIM. Washington, DC: U.S. Geological Survey. Biological Report 29. 45 p.
Van Winkle, W., C. C. Coutant, H. I. Jager, J. S. Mattice, D. J. Orth, R. G. Otto, S. F. Railsback, and M. J. Sale. 1997. Uncertainty and instream flow standards: perspectives based on hydropower research and assessment. Fisheries 22: 21-22.
WDFW and WDOE (Washington Department of Fish and Wildlife and Washington Department of Ecology). 2004. Instream flow study guidelines: technical and habitat suitability issues. WDFW and WDOE, Olympia, Washington.
The two-dimensional (2D) hydrodynamic modeling approach consists of:
The 2D modeling in turn consists of:
A number of two-dimensional flow models are used for analysis (FESWMS, River2D, Mike21, etc.), and new models are continually being created and adapted to address the concerns listed below. In general, the models are incorporated into a multi-dimensional surface modeling system, based on three-dimensional riverbed topography, flow rate, and downstream stage (i.e., water surface elevations) boundary conditions to calculate flow, velocities, water surface elevations, and boundary shear stresses in the channel. These have been used in channels with or without islands in both high and low Froude number flows (i.e., sub-critical and super-critical flow conditions).
The 2D modeling approach uses habitat criteria values (typically depth, velocity, and cover) from the literature in the same manner as IFIM and PHABSIM to determine the habitat-flow relationship for analysis species and life stages for the study reach. See Section 6.4.3 for a discussion of the use of 2D modeling to assess instream flows for amphibians.
4.1.3.1 Advantages and disadvantages of approach
Use of 2D modeling to assess instream flows has advantages and disadvantages relative to the other approaches evaluated, as discussed below:
Advantages
Disadvantages
4.1.3.2 Site-specific considerations and applicability
Many of the advantages and disadvantages of this approach will depend on site-specific considerations, as discussed below:
4.1.3.3 Selected references
Addley, R.C. and J.A. Ludlow 2001. Kerr Dam Ramping Rate Study Lower Flathead River. Final Report for the Confederated Salish and Kootenai Tribes. Utah Water Research Lab, Utah State University, Logan, Utah. 86pp.
Hardy, T.B. and Addley, R.C. 2001. Evaluation of interim instream flow needs in the Klamath River, Phase II Final Report (draft). Institute for Natural Systems Engineering, Utah State University.
Hardy, T. B., and R. C. Addley. 2003. Instream flow assessment modelling: combining physical and behavioural-based approaches. Canadian Water Resources Journal 28: 273-282.
Nelson, J.M. 1996. Predictive Techniques for River Channel Evolution and Maintenance. Water, Air and Soil Pollution 90:321-333.
Nelson, J.M. and J.D. Smith. 1989. Flow in meandering channels with natural topography, in River Meandering, Water Resour. Monog., Vol. 12, edit by S. Ikeda and G. Parker, pp. 69-102, AGU, Washington, D.C.
Steffler, P., and J. Blackburn. 2002. River 2D: two-dimensional depth averaged model of river hydrodynamics and fish habitat. Introduction to depth averaged modeling and user's manual. Prepared by University of Alberta.
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