ASPECTS OF IMPACT ASSESSMENT OF LOW FRESHWATER 

 INFLOWS TO CHESAPEAKE BAY 



G. Bradford Shea, G.B. Mackiernan, L. Chris Athanas, 



and D.F. Bleil 



Western Ecosystems Technology, Laurel, Maryland 



ABSTRACT 



Modification of the Chesapeake 

 Bay hydrologic environment has oc- 

 curred over the past several decades, 

 and is expected to continue at least 

 until the end of the century. An 

 attempt to assess the impact of low 

 freshwater inflows (due to drought 

 and consumptive losses) upon the 

 Chesapeake Bay biota is currently 

 underway. Some of the tools being 

 used in this assessment are 1) dis- 

 tribution, tolerance, and life his- 

 tory studies of selected estuarine 

 species, 2) hydraulic modeling of the 

 bay's salinity and circulation re- 

 gimes, and (3) computer simulation 

 of representative segments of the 

 ecosystem. The uses and limitations 

 of each are discussed. 



Critical life history stages, 

 habitat and food requirements, and 

 tolerance to physical stress have 

 been used to select representative 

 study species for evaluation of 

 effects of reduced freshwater flows. 

 This approach is limited by the in- 

 ability of species-by-species anal- 

 ysis to deal adequately with the 

 interrelationships between estuarine 

 organisms. Information on community 

 structure and trophic relationships 

 has been used to develop a conceptual 

 model of major energy flows within 

 the Chesapeake Bay ecosystem. A com- 

 puter simulation model will be used 

 to provide insight into the effects 

 of low flow, and the propagation of 



these effects throughout the eco- 

 system. The results of this study 

 will aid managers in planning con- 

 sumptive-use patterns of freshwater 

 flows into the estuary. 



INTRODUCTION 



The U.S. Army Corps of Engineers 

 has, among its responsibilities, that 

 of setting low flows on many Federal 

 water resource projects on regulated 

 rivers. In addition, in 1965, Con- 

 gress authorized the Corps, under 

 Section 312 of the River and Harbor 

 Act to 



"make a complete 

 investigation and 

 study of water util- 

 ization and control 

 of the Chesapeake 

 Bay Basin." 



This authorization included authority 

 to develop tools to study altered 

 flow conditions including a hydraulic 

 model. The investigation authorized 

 by Congress led to, among many other 

 products, a study of low flows and 

 their impact upon the biota of the 

 Chesapeake Bay and its tributaries. 

 This "Biota Assessment" was under- 

 taken beginning in 1979 by Western 

 Eco-Systems Technology (WESTECH) un- 

 der the auspices of the Corps of 

 Engineers and is still in progress. 

 The study area extends from the bay 

 mouth to the head of the tide, as 

 shown in Figure 1 . 



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