Framework to Determine Total Maximum Daily Flow Diversions for Fish Protection

Abstract

This paper describes a framework to determine the total maximum daily flow diversions (TMDFDs) of freshwater from the San Francisco Bay Delta that can be undertaken without causing the extinction of salmon, striped bass, and delta smelt. The framework comprises three models: the watershed analysis risk management framework (WARMF) model of tributary rivers, the Link-Node estuary model of the Bay Delta, and the monthly cohort life-cycle model of fish. The first two models simulate the environmental conditions of river segments and estuary “Nodes” in which fish live. The fish model deposits eggs in river segments on specified months. The eggs become larvae, juveniles, and young as they move downstream to the estuary “Nodes” where they may die, be eaten, or be entrained into pumps that divert water for export to northern and southern California cities and Central Valley farms. Thus, flow diversion is mechanistically connected to fish decline. These models are integrated by the graphical user interface (GUI) of WARMF to serve as a decision support system (DSS). The DSS allows users to enter alternatives of daily flow diversions, including no diversion. The DSS calculates projected fish declines. A stakeholder process is then used to select an acceptable water diversion plan.