Watershed Location and Conditions Affect Water Supply

		KRIS and Prop 50 Contents \| KRIS Web Home

Watershed Location and Conditions Affect Water Supply
Almost every winter northwestern California is blessed with ample rain and snow. The weather comes in cycles with periods of wet and dry, so water supply varies with the water year, but the timing and quantity of water flow from North Coast rivers and the ability to satisfy "beneficial uses" varies with watershed condition. Rainfall is highest in the Coast Range, while in the Klamath Mountains to the east precipitation also falls as snow. Rain shadows make some interior basins very dry. Changes in runoff relative to land management can vary more widely at elevations subject to rain-on-snow events. Prop 50 should help us understand how to treat watersheds where precipitation is abundant so as to maximize the reliability and quality of the North Coast's surface waters.	NOAA Doppler Radar image
Chart from KRIS Klamath-Trinity V 3.0 shows pre and post-dam flow frequency for the Trinity River. Discharge =log of flow in cubic feet per second. Pre-Dam Flow 1912-1963, Post Dam = 1964-1999. From McBain & Trush (1998).
Rainfall, flow, and water quality data can be captured in a regional information system using KRIS technology so that scientists can study patterns of precipitation, flow peaks and changes in aquatic habitat and species diversity. The example above is a chart of pre-dam and post-dam Trinity River flows. Until all such data from watersheds in the North Coast IRWMP region are assimilated and available for scientific comparison, relationships of watershed condition, beneficial uses of water and water supply will remain unknown. Once linkages are recognized, water resources in northwestern California can be more effectively protected and restored, as required under Prop 50.
Healthy Watersheds Provide More Reliable and Higher Quality Water
Photo from KRIS Coho	Photo from KRIS Coho
Northern California's rivers and streams are one of its greatest assets. They provide drinking water and recreational benefits, and support diverse aquatic life, including Pacific salmon species that are important both culturally and economically in the region. Healthy watersheds absorb rainfall and release some as stream flow during major storms. They also retain water in aquifers, which is then released more slowly during dry seasons.
Photo from KRIS Klamath-Trinity V 3.0.	Case studies in northwestern California show that problems with stream health and water supply can occur when watersheds are managed too intensively. If thresholds of prudent risk are exceeded, such as when most vegetation in a watershed is removed in a short period of time or an area is urbanized, the frequency of damaging floods increases. Unfortunately there are numerous rivers and streams in the North Coast region today where sediment yield is so high that surface flow is lost during annual summer low flow periods. These streams are recoverable over time as watersheds heal and the sediment supply is abated. Infrequent, major floods my cause some sediment yield even in healthy watersheds, but scientific studies show flood frequency and damage is elevated in watersheds with a history of disturbance. Prop 50 funded KRIS projects will provide a platform for studies to determine prudent risk for land use management and how to control flood damage and loss of fish habitat and to maximize the supply of clean water.