Figure Page 



20 The effects of groins on littoral drift 109 



21 Types of breakwaters and littoral barriers where sand 



transfer systems have been employed 110 



22 Recession of beachfront in response to a relative rise 



in sea level over a shore slope of one percent Ill 



23 A sample sediment and erosion control plan 114 



24 A temporary retention basin that prevents serious water 

 pollution from eroded soil 115 



25 Sod (A), straw mulch (B), and willow whip (C), methods 



for protecting a steep slope from erosion 116 



26 Typical hydrographic changes due to increasing the area 



of impermeable paved surfaces in a developing area 118 



27 An i roperly designed artificial lake or borrow pit 120 



28 A typical configuration of a canal and oil drilling 



barge slip in Louisiana 123 



29 A typical profile of aquifers of Long Island, New York .... 131 



30 The pattern of saltwater intrusion (salinities in 

 parts per million) of the Biscayne aquifer in the 



vicinity of Miami, Florida 132 



31 Th effects of withdrawal of water from an aquifer 133 



32 The effects of overpumping the groundwater on ground- 

 water level decline (a) and subsidence (b) in the 

 Houston-Galveston Bay area, Texas, in the period from 



1906 to 1964 134 



33 Components and processes of a secondary sewage treatment 



plant 136 



34 Advanced wastewater treatment showing the biological - 

 chemical method employed to activate sludge treatment 



with alum addition and ni trification-dentrification 139 



35 Typical septic tank detail 141 



36 Directional drilling technique for the installation of 

 pipelines under rivers and streams 147 



37 Large, well-engineered detention pond and sediment 



basin dam 151 



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