connected. Localized changes of several important hydrologic character- 

 istics, such as depth of the standing water, duration of submergence, 

 frequency of submergence/emergence may ultimately lead to localized 

 changes in plant assemblages. 



Of greater significance, however, are the hydrologic effects of dredging 

 pipeline channels and placing spoil. Canals that are adequately back- 

 filled and/or plugged may have localized effects on circulation patterns, 

 but they do not result in long continuous channels and spoil ridges. 

 Water movement patterns remain essentially unchanged following restora- 

 tion procedures. 



Open, unplugged channels bordered by continuous spoil levees generate a 

 complex of interactions which may change the amount of standing water and 

 other important hydroperiod regulators. Factors such as deployment 

 patterns, canal depth, and levee height can interact to produce intra- 

 marsh situations in which waters are either drained, impounded, or 

 diverted. Long continuous canals intercept freshwater sheetflow from 

 upland areas, thus facilitiating more rapid marsh drainage. Associated 

 spoil levees block or redirect sheetflow, preventing its entry into 

 portions of the marsh. Levees may also isolate interior zones. Resul- 

 tant changes in average water depth, length of submergence, and frequency 

 of fluctuation may ultimately generate changes in the area's biota, if 

 the alterations are extensive. Small upland fresh marshes traversed by 

 open pipeline ditches may be converted to drier systems by this increased 

 drainage. The magnitude of alterations described above vary according to 

 channel dimensions, number of channels, channel orientation relative to 

 freshwater and saltwater sources, levee orientation and placement, the 

 hydrologic gradient of the watershed, and other site-specific character- 

 istics. 



Channel excavation increases total suspended sediments. Secondary 

 effects in emergent vegetation areas are typically temporary and 

 localized in areal extent. In open-water sites, increased suspended 

 sediments temporarily increase water turbidity and sedimentation rates, 

 as well as local biological oxygen demands. Sediment dispersion, however, 

 may affect more extensive areas, depending upon prevailing water veloci- 

 ties and circulation patterns. Increased water turbidity can briefly 

 inhibit submergent and phytoplanktonic productivity. Increased biolog- 

 ical oxygen demand may temporarily deplete dissolved oxygen levels, thus 

 stressing nearby fish and aquatic invertebrate populations. Barren spoil 

 banks or levees contribute to prolonged increases in the amount of sus- 

 pended sediments via erosion and runoff. Establishment of plant ground 

 cover moderates such erosion. 



Disturbances associated with pipeline channel construction, line instal- 

 lation, and cleanup procedures typically cause short-term displacement of 

 sensitive wildlife species from otherwise favorable habitats nearby. 

 Displacement may affect feeding waterfowl concentrations, bird rookeries, 

 and vertebrate movement patterns. Following project completion, species 



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