and are usually most damaging to juvenile and sessile species. In 

 addition the crossing area may be sufficiently disrupted that pre- 

 construction conditions may not be obtained due to constant agitation 

 and erosion from fast moving currents. Blasting or dredging may be 

 required in these crossings. 



An adaptation of oil well directional drilling techniques has been 

 used to install pipes at river crossings, and while the techniques are 

 more intricate than dredging a trench, the environmental effects are less, 

 The method involves drilling the pipe in an underground arc from one side 

 of the stream to the other (Figure 36). 



Figure 36. Directional drilling technique for the installation of 

 pipelines under rivers and streams (Source: Reference 108). 



The advantages of boring a crossing section under a river or stream 

 include the ability to work in any period during the year and completion 

 of the project within minimal time, usually two to six weeks. Also, as 

 the stream bed and its banks are undisturbed, costly bulkheading and 

 other bank stabilization methods are eliminated. Weight coating the 

 section of pipe is not necessary. The line is buried deep beneath the 

 stream bed and as the earth above is undisturbed, there is no buoyancy 

 problem. Additionally, there are no navigational hazards for large or 

 small boats during or after construction. 



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