bricks with corner lags to control spacing to perforated bricks [71]. 

 Porosity varies with the subsoil and the amount and type of subsurface 

 gravel . 



4.6.4 Line Construction 



On-site line construction activities, including pole and power 

 lines, underground communication lines, and small pipelines, will 

 normally disturb only a small amount of land and, if expeditiously 

 restored, may have minimal effects on fish and wildlife resources. 

 Excess spoil generated from these construction corridors may cause 

 a spoil placement problem. 



4.6.5 Erection of Structures 



The activities of construction should have minimal environmental 

 effects providing no adverse effects are caused by foundation excavation. 

 However, the operation of trucks, heavy equipment, and other supporting 

 activities could have a variety of adverse effects. Heavy metal 

 contaminants may be released from metal fabrication, paints, and other 

 building materials and supplies used during construction. 



4.6.6 Open Excavations 



Canals built to drain lowlands or to facilitate navigation can affect 

 the ecosystem. For example, waterway excavation can (1) pollute coastal 

 waters, (2) preempt vital habitat areas, and (3) alter natural water flow 

 patterns. (For details see Artificial Waterways, Section 4.7.) 



In areas with high water tables, excavation should be confined to 

 works that are specifically designed to preserve the natural water 

 system. Artificial basins should be shallow and have gently sloping 

 vegetated earthen sides (Figure 27). Artificial basins should be surround- 

 ed by a buffer strip of vegetation for bank protection and filtration of 

 runoff. Dead-end canals serve as traps for silt and organic ooze, 

 accumulating deep beds of anaerobic materials which cause persistent 

 lowering of oxygen to unacceptable levels. During storms such sediments 

 partially flush out into estuarine waters, causing stress through the 

 reduction of dissolved oxygen levels. 



Land drainage has a particularly high potential for adverse effects 

 on fish and wildlife resources. When water tables are lowered with 

 drainage canals, the natural flow pattern is disrupted, the water- 

 cleansing function of the vegetation is eliminated, and runoff occurs in 

 surges. 



4.6.7 Wetlands Safeguards 



The natural characteristics of wetlands are so valuable that 

 perservation of their functional integrity should be miantained 

 and, if oossible, integrated with man-made alterations. Any use 



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