Water-level declines in the river have substantially changed long-term hydrologic conditions in more than 200 miles of off-channel floodplain sloughs, streams, and lakes and in most of the 82,200 acres of floodplain forests in the non-tidal reach of the Apalachicola River. Decreases in duration of floodplain inundation at low discharges were large in the upstream-most 10 miles of the river (20-45 percent) and throughout most of the remaining 75 miles of the non-tidal reach (10-25 percent). As a consequence of this decreased inundation, the quantity and quality of floodplain habitats for fish, mussels, and other aquatic organisms have declined, and wetland forests of the floodplain are changing in response to drier conditions. Water-level decline caused by channel change is probably the most serious anthropogenic impact that has occurred so far in the Apalachicola River and floodplain. This decline has been exacerbated by long-term reductions in spring and summer flow, especially during drought periods. Although no trends in total annual flow volumes were detected, long-term decreases in discharge for April, May, July, and August were apparent, and water-level declines during drought conditions resulting from decreased discharge in those 4 months were similar in magnitude to the water-level declines caused by channel changes. The observed changes in seasonal discharge are probably caused by a combination of natural climatic changes and anthropogenic activities in the Apalachicola-Chattahoochee-Flint River Basin. Continued research is needed for geomorphic studies to assist in the design of future floodplain restoration efforts and for hydrologic studies to monitor changes in the future flow regime of the Apalachicola River as water management and land use in this large tri-state basin continue to change. The report is available at https://pubs.usgs.gov/sir/2006/5173/
In this article, I describe the importance of large river-floodplain ecosystems and some of the consequences of altering their natural processes, functions, and connectivity. Then I contrast the species-focused management typically employed by natural rescue agencies with the ecosystem approach. I define ecosystem management as working with the natural driving forces and variability in these ecosystems with the goal of maintaining or recovering biological integrity. I focus on flood pulses both because they drive these systems and because the great floods of 1993-1994 in Asia, Europe, and North America heightened public awareness, thereby creating an opportunity to change river management policies.
I draw my examples largely from the upper Mississippi River and Illinois River because I am most familiar with them. They also exemplify both the conflicts between development and conservation of large floodplain rivers that have occurred world wide and the more recent restoration and rehabilitation efforts that are beginning in Europe and the United States.
The Mississippi River and Illinois River comprise the Upper Mississippi River System, which the US congress designated as both a "nationally significant ecosystem" as well as a "nationally significant waterway" in the Water Resources Development Act of 1986.Plans for even greater expansion of navigation capacity are currently being developed by the US Army Corps of Engineers. But federal and state natural resource agencies and several environmental groups fear that the integrity of the upper Mississippi is being compromised. They have issued their own strategies and plans for conserving and restoring the river.
The hydrologic regime of the Illinois River has been altered over the past 100 years. Locks and dams regulate water surface elevations and flow, enabling commercial navigation to continue year round.
Healthy fish populations are dependent on streamflow regimes that protect the ecological integrity of their habitat. Fish habitats are the consequence of linkage among the stream, floodplain, riparian, and upland zones, and watershed geography. Fluvial-geomorphic processes form and control fish habitat. Because of this, multiple in-channel and out-of-channel flows are needed to maintain these processes. We present a conceptual methodology for measuring tour types of streamflow regimes: instream flows, channel maintenance flows, riparian maintenance flows, and valley maintenance flows. The combination of these four streamflow types is designed to protect fish and their habitat. Using a case study of the Salmon River near Whitebird, Idaho, we demonstrate how the methodology could be used to develop a multiple flow recommendation.