Part I: Hydroelectric Project Effects Matrix
This matrix (Table 1) is intended to provide a fairly comprehensive accounting of potential effects at a generic hydropower project, and does not prioritize certain effects as being more important than others. The matrix includes only those potential effects with a nexus to hydropower facilities or operations, and those that may typically warrant study. Depending on the characteristics of a specific hydropower project, many of these effects may not be manifest, while others may be significant and warrant assessment. This matrix is intended as a tool to examine the effects of an existing hydropower project (typically during relicensing), and is not intended for assessing proposed construction (although many of the same effects could be considered).
A given project feature may have a positive or negative effect on a specified resource. For example, diversion dams can alter river temperatures downstream, but study would be needed at a particular project to determine if the temperatures are increased (e.g., via reduced instream flows or epilimnetic releases) or decreased (e.g., via hypolimnetic releases), and whether the altered condition is "good" or "bad" for the affected environmental resources. Therefore, this matrix refers to most effects as "altering the condition" relative to a natural or pre-project condition, and avoids pre-judging site-specific effects as adverse or beneficial. Only ecological relationships affected directly by hydropower projects were considered for this matrix. For example, indirect effects such as turbidity resulting from road runoff that potentially decreases foraging efficiency for fish were not considered. In addition, 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) were not included, although they can be significant in some projects. Other types of potentially significant effects that were considered outside the scope of this matrix include:
- Catastrophic events, such as failures of dams or canals,
- Cumulative effects of a hydropower project (or multiple projects) within a watershed, and
- Effects on human health, such as those related to a decline in traditional fish-based food resources.