of this occurring at the Prospect Creek material site near the Trans-Alaska 

 Pipeline. This increased flow can cause erosion of the surface of the buffer, 

 especially any disturbed area. It can also cause scour or headcutting in the 

 material site because of the I arger-than-des i gn flows during breakup. The 

 safety factor applied to buffer width should be increased if channel aufeis is 

 known to develop at the site. 



BUFFER HEIGHT 



Buffer height and buffer width are interrelated to a certain degree. 

 If the buffer is high enough to keep all but the largest of floods out of 

 the material site, only bank erosion needs to be considered in buffer design. 

 This may be the situation for many material sites located on terraces. If the 

 buffer is low and is flooded frequently by larger flows, erosion of the sur- 

 face of the buffer, headward erosion of the upstream face of the material 

 site, and scour within the site must be considered in the buffer design. The 

 height of natural buffers is fixed at the level provided by nature. Design 

 options include increasing buffer width to account for low height, building up 

 the buffer height by adding a dike on the river side, or building a completely 

 separate buffer structure. These options are discussed in more detail in a 

 subsequent paragraph. 



To evaluate the frequency of flooding, hydrologic and hydraulic analyses 

 must be carried out. The details of these analyses are too complex to explain 

 here, but appropriate references are given to allow the user to study the 

 subject further. 



• A hydraulic analysis is required to evaluate what discharge will ini- 

 tiate overtopping of the buffer. Cross sections of the river, extending 

 up to the level of the buffer on both banks, are necessary for this 

 analysis. It is preferable to have five or more cross sections through 

 the reach of river adjacent to the buffer. The Manning equation or, 

 perferably, a backwater program, should be used to calculate the dis- 

 charge corresponding to the stage that would overtop the buffer. Discus- 

 sions of these analyses are provided in most open-channel hydraulics 



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