|Abstract or Summary
- A problem confronting the Corps of Engineers and other water resources planners in the Pacific Northwest is the prediction of anadromous fish enhancement benefits that would result from a proposed high dam project. These benefits are expected from augmenting natural streamflows with relatively cold reservoir withdrawals. The resulting increased streamflows and decreased river temperatures downstream are expected to sustain larger salmon populations than would occur without an impoundment.
The objectives of this study are to develop a computer simulation model for continuously predicting reservoir and downstream temperatures and mass flows for a single high dam system; and to demonstrate how the model could be used in an actual planning situation to provide information on anadromous fish production.
The reservoir submodel constructed for this study is based upon the stratified reservoir model developed at M.I.T. A downstream bulk flow river temperature and routing algorithm, solar flux submodel, and several decision submodels are constructed and incorporated into this system. The model permits determination of all values of mass flows, depths, and water temperatures at any designated point in time for specified points along a river, and for specified reservoir elevations. The model structure allows decision routines to be called at each time interval update for determining reservoir withdrawal, the amount of withdrawal from each of three specified reservoir outlets, and the channel withdrawal for irrigation.
This model is applied to the proposed 145,000 acre-feet
reservoir on the Calapooia River at Holley, Oregon, to investigate the
expected trade-offs and product mix between anadromous fish (a
function of water temperature and streamflow) and reservoir-based
recreation (a function of reservoir elevation).
It was found that the river temperatures downstream from the
proposed reservoir could not be maintained within the optimum range
for Pacific salmon. Further, it was found that the temperatures of
the reservoir withdrawals would have a negligible effect upon river
temperatures beyond 24 miles downstream from the dam site.
An economic analysis suggests that the level of anadromous fish
enhancement and recreation benefits predicted by the Corps of Engineers could not be achieved by constructing the proposed Holley
The model developed in this study is structured so that any
water quality parameter, not just temperature, could be simulated
with the downstream routing algorithm. The model can also be used
to evaluate the operational efficiency of existing multiple objective
water projects. In addition, the model structure would make it
relatively easy to build additional submodels into the algorithm. For
example, the inclusion of a flood control or dynamic fish population
submodel would depict a more realistic situation as well as broaden
the economic analysis.
The computer model structure requires the solution sequence to
pass through all relevant subprograms at each time interval update.
Thus, calculations covering only one internal time period are made
on each pass of a subprogram. This model structure allows for considerable
operating flexibility. For example, because all hydrometeorological
data are read from subprograms, the model can be
operated using either historical or stochastically generated data.