Review of the St. Johns River Water Supply Impact Study Final Report (2012) / Chapter Skim
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4 Overarching Themes and Conclusions
4 Overarching Themes and Conclusions
Pages 96-106
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From page 96... ...
In this regard, the District should be applauded for the scale and seriousness of the efforts expended to evaluate potential impacts of water withdrawals on the hydrology of the river and on the major components of the aquatic and semiaquatic ecosystems of the river system. The scope of the studies undertaken in the WSIS was unusually comprehensive relative to other environmental impact analyses with which the Committee members are familiar.
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From page 97... ...
Summing these effects over all workgroups leads to the same results apparent in the final column of Table 4-1: moderate effects are likely in the lower river due to salinity and flow rate issues, and in the upper river due to changes in water levels. The District's approach of using the lowest denominator in terms of a level of effect -- across all metrics within a workgroup, across hydrologic drivers in Table 4-1, and across workgroups in Table 4-2 -- represents an application of the precautionary principle that is appropriate.
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From page 98... ...
. Salinity Water Age Overall River Entraiment Flow Water Segment Rate Level & (excluding E&I)
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From page 99... ...
, District scientists indicated the level of uncertainty associated with each ranking based on three factors: availability of a predictive model, existence of supporting evidence, and the workgroup's understanding of the mechanism for an effect. For Tables 4-1 and 4-2, the largest uncertainty ranking given for a workgroup was used.
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From page 100... ...
Several critical issues that are beyond the control of the District or were considered to be outside the boundaries of the WSIS limit the robustness of the conclusions. These issues include future sea-level rises and increased stormwater runoff and changes in surface water quality engendered by future population growth and land-use changes.
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From page 101... ...
Finally, insofar as the MFL regulations limit the withdrawal allowable during low flow periods, these conclusions may be technically correct, but the Committee maintains substantial concern as to whether MFLs will be rigidly enforced in the future. If there is an extended drought in the future, when increased water supply demands have led to surface withdrawals, water suppliers might not be able to withdraw water from the river for months or even years on end.
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From page 102... ...
It most likely is true that such changes would not have important ecological effects on the main channel of the St. Johns River and on its large tributaries, and in this respect they can be considered to fall outside the "narrow confines of the WSIS." Nonetheless, such effects are likely to be important in smaller streams draining newly urbanizing areas (which are giving rise to the need for surface water withdrawals from the St.
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From page 103... ...
Second, District scientists and administrators felt that a focus on the potential effects of water withdrawals on the main channel of the St. Johns River was a sufficiently complicated (and costly)
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From page 104... ...
The primary conceptual model driving the WSIS can be summarized as follows: Increased Changes in Changes in Responses of biotic water water levels aquatic and components of river withdrawals and flows wetland habitat and wetlands In most cases, the direct effects of water withdrawals on biotic components of the river and associated wetland ecosystems thus were viewed as mediated by changes in habitat conditions. In some cases, however, such as plankton and SAV responses, water quality changes induced by biogeochemical process changes associated with changes in water levels also were considered to be potential drivers of change.
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From page 105... ...
2011. Chapter 2 – Comprehensive Integrated Assessment of the draft final Water Supply Impact Assessment report.
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