This will be a multi-disciplinary 

 effort involving economists, tidal 

 hydrologists , social scientists, en- 

 gineers, and biologists. These data 

 will also be important in estab- 

 lishing the relationship between 

 freshwater inflows and salinities in 

 terms of both the effects of various 

 quantities of inflow and the time it 

 takes for salinity levels to respond 

 to changes in flow (reaction time). 



It would be difficult, however, 

 to determine from these data the role 

 of each tributary in controlling 

 salinity levels, especially in a 

 geographic perspective. To accom- 

 plish this it will be necessary to 

 conduct another series of tests on 

 the model (sensitivity tests). In 

 these sensitivity tests, each major 

 tributary to Chesapeake Bay will be 

 analyzed separately. A one-year 

 hydrograph of the natural freshwater 

 inflows which occurred during the 

 drought of record will be simulated 

 in all tributary rivers except one. 

 In that river, the freshwater inflows 

 will be depressed by anticipated year 

 2020 consumptive losses. This will 

 be repeated until all major tribu- 

 taries have been addressed. 



The third, or plan formulation 

 series of low flow model tests, will 

 be oriented to formulating a schedule 

 of freshwater inflows for each major 

 tributary which will allow for a 

 healthy biota consistent with social 

 and economic feasibility. The tests 

 to be run will be based on the model 

 tests, impact analyses, and a screen- 

 ing of alternative freshwater inflow 

 levels . 



BIOTA ASSESSMENT 



A methodology for assessing the 

 impacts of reduced freshwater inflows 

 on the biota of Chesapeake Bay has 

 been developed and is being applied 



by the consulting firm of Western 

 Eco-Systems Technology (WESTECH) 

 under contract with the Corps of 

 Engineers. In view of the importance 

 of this work, the fact that there is 

 little precedence for it, and the 

 fact that WESTECH is working right at 

 the state-of-the-art, the Chesapeake 

 Bay Study Steering Committee and the 

 Fish and Wildlife Service are inti- 

 mately involved providing guidance 

 and review of the work as it prog- 

 ressses . 



Recognizing that it is impossi- 

 ble to address all of the over 2,700 

 species that live in Chesapeake Bay, 

 WESTECH developed, through an in- 

 tensive screening process, a list of 

 over 55 study species. The present 

 known and potential distribution of 

 these species, average salinity, and 

 known substrate were then plotted on 

 maps. These maps will be the basic 

 tool used in the evaluation of the 

 primary impacts of flow changes. 

 Additional maps will be prepared 

 reflecting each set of hydraulic 

 model salinity data. A determina- 

 tion will then be made of the varia- 

 tions in available habitat caused by 

 salinity changes. These habitat 

 variations will be used in assessing 

 the primary biological impacts of 

 flow reductions. 



The next step will be the as- 

 sessment of secondary impacts. This 

 is an extremely difficult task be- 

 cause it involves not only the rela- 

 tionship between salinity and orga- 

 nisms, but the interrelationship 

 among species and families of spe- 

 cies. Because a sufficient data base 

 is not available to address these in 

 any great detail, the secondary im- 

 pact assessment methodology consists 

 of a systems analysis based on a 

 conceptual model and the best avail- 

 able scientific judgments. 



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