DETERMINATION OF ECOSYSTEM STREAMFLOW NEEDS CONSIDERING CLIMATE CHANGE AND GROUND WATER USE

The determination of riverine ecosystem needs must consider a variety of uses by the ecosystem. In this paper the Gunnison River below Blue Mesa reservoir in western Colorado is used as an example illustrating the calculation of riverine ecosystem streamflow needs. Calculation streamflow needs for the lower Gunnison River must consider needs of the riparian zone, of trout during winter in some reaches, of winter versus spring ecosystem needs in different reaches, and the need to move sediment. Sediment movement in the lower river and the needs of the native riparian zone requires high streamflows in the spring. In contrast, the needs of a blue ribbon fishery in the Gunnison Gorge reach requires stable moderate stream flows in both the winter (moderately low) and in the spring (moderately high). There is also a possibility that climate change may have an impact on the sediment delivered to the stream because of possible changes in the summer thunderstorms. The potential impact of climate change on the sediment dynamics in the Gunnison River must be considered in establishing ecosystem flow needs. Another consideration in the calculation of ecosystem needs in rivers is the impact of urbanization on streamflows. Examples of changes in the streamflow caused by urbanization are streams in the Puget Sound region. Urbanization will change the characteristic of the streamflows by increasing flashiness of the flows and by ground water withdraws. Both of theses are important riverine ecosystem considerations.