Optimal groundwater management with GIS applications for the Blue Lake Aquifer of Humboldt County, California

This study investigated optimal groundwater management in the Blue Lake Aquifer system of Humboldt County, California. A linked-simulation-optimization model was developed to aid in the creation of an optimal pumping schedule. The objective was to minimize the discounted operational cost of four Ranney wells over a 5-year planning horizon. Several other past studies have also focused on optimal groundwater management in this aquifer. The goal of this project was to develop a more-accurate groundwater simulation model. New information on geomorphic features was incorporated into the model. This information was previously unavailable to past investigators. This study also utilized geographic information systems to compile and analyze the data, and properly-georeference it in the model. The study investigated four scenarios. Scenario 1 used constant water demands for the 5-year period. This was the base case to which the other scenarios were compared. In Scenario 2, the demands were increased by 5% each year from years 2 through 5. Scenarios 3 and 4 investigated the changes in model results due to changing the aquifer's hydraulic conductivities. In Scenario 3, the hydraulic conductivities were reduced by an order-of-magnitude. In Scenario 4, the hydraulic conductivities were increased by an order-of-magnitude. Results showed that Scenario 2 was the most expensive. Increasing the demand had the largest effect on the cost. Scenario 3 was the second-most expensive. Lowering the hydraulic conductivities allowed less water to recharge the areas in the vicinity of the wells. This resulted in lower head levels in these critical areas. Since the cost function was based on the lift needed to extract the water from the ground, the cost was increased. Scenario 1 had the second-lowest costs. This low cost was attributed to having stable demands, and medium-range hydraulic conductivities. Scenario 4 was the least expensive. Higher hydraulic conductivities allowed more water to recharge the areas in the vicinity of the wells. This resulted in the highest head levels in these critical areas, reducing the lift cost.