Bioeconomic modeling of floating aquatic weeds in the Sacramento–San Joaquin River Delta

This study develops a preliminary bioeconomic model that links an aquatic weed growth model to an economic model to evaluate the cost of alternative weed management policies in the Sacramento–San Joaquin Delta (Delta). During the past decade the costs to manage both floating and submerged invasive weeds in the Delta between 2013 and 2017 was estimated to be at least $60 million. The bulk of the costs are incurred by the California Division of Boating and Waterways (CDBW), whose areawide weed management program is a public good that influences the costs of aquatic weed management for all other public and private agencies on the Delta. One of the main aquatic weeds managed by CDBW is water hyacinth. Normally, weed control activities can begin in March in areas in the southeast portion of the Delta, and in June elsewhere. This study examines the relative costs incurred by CDBW of starting all weed control in March under three different weed growth model assumptions, and two herbicide efficacy assumptions. Costs fall by 16.4% under the slowest growth rate model and by 73% under the fastest growth rate model. Environmental concerns over the protection of native fish spawning areas may prevent the earlier adoption of herbicide control; however, the results show that investments in control methods that are both fish friendly and effective at controlling weed populations may reap substantial weed management cost savings.