4. Basic travel time model
4.1. Introduction

From a management standpoint, understanding and modeling juvenile salmonid travel time is important for several reasons. The ability to predict the arrival times of populations of fish at dams will aid in directing river and dam operations to enhance fish survival. For instance, spilling fish over the top of dams is considered to be a safer passage route than through the turbines. However spilling water for fish passage involves a cost of lost electricity generation, so predicting the abundance of fish in front of dams can help to make this process as efficient as possible. Also, there is the question of whether it is possible to speed up migration rate. Since river currents are thought to be a primary source of downstream movement (Smith, 1982), the reduced river velocity created by dams can potentially greatly increase the travel times of the juveniles. In fact, Raymond (1978) estimated that the construction of dams may have doubled the travel times of some stocks in low flow years. A proposal that is receiving serious consideration is reservoir drawdown. This involves lowering reservoir levels to try to enhance river velocities. Understanding how fish respond to these conditions will be crucial.

In this chapter, I develop a basic travel time model where migration rate is considered to be constant, and all members of a cohort behave identically. In the next chapter, I incorporate behavioral components into the travel time model, such as travel time related mortality, migrational delay, and diel variation in migration rate. In chapter 6, I allow for population heterogeneity, with the migration rate of individuals being determined by factors such as fish length.