A New Conceptual Model to Understand the Soil-Water Budget in the Scott River Watershed

The Scott River is one of four major tributaries in the Klamath River Basin that provide cold water habitat for salmonid populations. At the same time, the Scott Valley entertains extensive alfalfa and hay productions that provide the economic base for the agricultural valley. Due to the Mediterranean climate in the area, discharge rates in the river are highly seasonal.  Almost all annual discharge occurs during the winter precipitation season and spring snowmelt. During the summer months (July through September), the main-stem river becomes disconnected from its tributaries throughout much of Scott Valley and relies primarily on baseflow from the Scott Valley aquifer. Scott Valley agriculture relies on a combination of surface water and groundwater supplies for crop irrigation during April through September. The need to guarantee a sustainable water quality (mainly in-stream temperature) for the native salmon population and the necessary amount of water for agriculture suggested the importance of developing a new conceptual model for the evaluation of the soil-water budget throughout the valley. The model takes into account precipitation as main input and then, based on the information on crops, water sources and irrigation practices provided by the local groundwater committee, calculates for each field the amount of water used for irrigation, the evapotranspiration, the soil moisture and the water that will be available as groundwater recharge. The simulated period goes from October 1990 to present. The field-based, local-scale analysis allow the test of different management alternatives and their impact on pumping and recharge to groundwater and on streamflow. The soil-water budget model is also designed to be coupled with a surface water/groundwater flow model currently in development.