This volume is the first of a two-part set addressing methods for assessing the cumulative effects of hydropower development on fish and wildlife in the Columbia River Basin. Species and habitats potentially affected by cumulative impacts are identified for the basin, and the most significant effects of hydropower development are presented. Then, current methods for measuring and assessing single-project effects are reviewed, followed by a review of methodologies with potential for use in assessing the cumulative effects associated with multiple projects. Finally, two new approaches for cumulative effects assessment are discussed in detail. Overall, this report identifies and reviews the concepts, factors, and methods necessary for understanding and conducting a cumulative effects assessment in the Columbia River Basin. Volume 2 will present a detailed procedural handbook for performing a cumulative assessment using the integrated tabular methodology introduced in this volume. 308 refs., 18 figs., 10 tabs.

A hypothetical example of multiple hydroelectric development is used to demonstrate the applicability of the integrated tabular methodology (ITM) that was recommended for cumulative effects assessment in Volume 1. The example consists of an existing mainstem dam and four proposed small hydroelectric developments in a small river basin containing elk summer and winter range and chinook salmon spawning areas. Single-project impact assessments are used collectively in the methodology to estimate the cumulative effects of the projects on elk and salmon. The steps in cumulative assessment are (1) establishing a conceptual and schematic representation of each cumulative effect, (2) calculating interaction coefficients for each pair of projects, (3) developing interaction and impact matrices, (4) multiplying these matrices, (5) evaluating the contribution of shared project features to cumulative effects, and (6) incorporating the effects of already existing projects. The ITM is most effective when single-project assessments are accomplished in a detailed, quantitative manner. The methodology involves the use of impact response curves (such as fry emergence as a function of fine sediment or habitat suitability as a function of road density) for each impact being assessed. 14 refs., 15 figs., 16 tabs.