available to simulate in the bay the 

 depression in river flows associated 

 with consumptive water use. 



On the other hand, a drought or 

 depressed freshwater inflows can be 

 simulated at any time on the Chesa- 

 peake Bay Model as can nearly any 

 other hydrologic event. The fact 

 that the model is built to a hori- 

 zontal scale of 1 to 1000 and a 

 vertical scale of 1 to 100 means that 

 Chesapeake Bay has been reduced to 

 less than eight acres, a manageable 

 size which allows for the ready, 

 relatively inexpensive collection of 

 data. And with a time scale of 1 to 

 100, one year's data can be collected 

 in a little over 3.5 days. Pictures 

 of the model and the 14-acre shelter 

 housing it are shown in Figures 3 

 and 4. 



HYDRAULIC MODEL TESTS 



In order to accomplish the ob- 

 jectives of the Chesapeake Bay Fresh- 

 water Inflow Study, it will be neces- 

 sary to conduct a series of three 

 tests on the hydraulic model, i.e., a 

 problem-identification test, a sen- 

 sitivity test, and a plan formulation 

 test. Both the problem-identifica- 

 tion and the sensitivity tests focus 

 on identifying the magnitude of the 

 problem and determining the rela- 

 tionship between freshwater inflows 

 and salinities. The plan formulation 

 test is oriented to the formulation 

 of minimum acceptable freshwater in- 

 flows from each of the major bay 

 tributaries. In each test, a re- 

 presentative variable long-term 

 average tide and a weekly hydrograph 

 of freshwater inflows will be used. 

 Both of these will be controlled by a 

 computer. 



The purpose of the problem iden- 

 tification test is to determine bay- 

 wide salinity levels during a drought 

 of record under both natural flow 

 conditions and flow conditions re- 

 duced by projected consumptive loss- 

 es. This test will be done in two 

 parts. The first, or base part, will 

 focus on establishing the salinity 

 structure of the bay during natural 

 drought conditions and determining 

 the amount of time it takes to re- 

 cover from a drought to a condition 

 of dynamic normality. This will be 

 done by simulating on the model the 

 three low flow years of the worst 

 drought of record (1964, 1965, and 

 1966) followed by two years of aver- 

 age freshwater inflow conditions. The 

 second, or future part of the test, 

 will be concerned with the magnitude 

 of change in salinities which would 

 be caused by high consumptive uses of 

 water during a severe drought. As in 

 the first part, a five-year hydro- 

 graph of freshwater inflows will be 

 simulated in the model. In this 

 case, however, the natural inflows 

 during the three drought and two 

 average inflow years will be reduced 

 by an amount equal to the uncon- 

 strained consumptive losses predict- 

 ed to occur in the year 2020. A com- 

 parison of the data from the base 

 and future parts of the test will 

 yield the changes in the salinity 

 regime resulting from decreased 

 freshwater inflows. 



The data from both of these 

 parts will be used as the basis for 

 specifically defining existing and 

 potential problems as they relate to 

 both short- and long-term reductions 

 in freshwater inflows and in ascer- 

 taining the environmental, social, 

 and economic consequences of low 

 freshwater inflows. They will also 

 be used as a basis for formulating 

 minimum freshwater inflow criteria. 



122 



