erosion techniques. Cross sections are surveyed as shown (two additional 

 cross sections were collected further downstream). A backwater analysis was 

 run to find that discharges of 103 m /s and 89 m /s overflowed the buffer at 

 Cross Sections 3 and 7, respectively. A flood frequency analysis indicated 

 that these discharges had recurrence intervals of 35 and 25 years. The design 

 life of the buffer is 25 years. Thus, from Table A-l, at Cross Section 7 there 

 is a 64 percent chance of getting flow into the downstream end of the material 

 site within the 25-year life. This chance is acceptable to the user because 

 the flow would primarily be backwater and would have relatively low erosion 

 potential. At Cross Section 3 the upstream buffer has a 50 to 60 percent 

 chance of overtopping the buffer. The user finds this to be unacceptable, but 

 since there is a relatively small chance of substantial flow entering the pit 

 from the upstream side, he recommends riprapping the upstream bank of the pit. 



REFERENCES 



Bovee, K. 0., and R. T. Milhous. 1978. Hydraulic Simulation in Instream Flow 

 Studies: Theory and Techniques. Instream Flow Information Paper No. 

 5. Cooperative Instream Flow Service Group. Fish and Wildlife Service. 

 Fort Collins, Colorado. 125 pp. 



Br ice, J. 1971. Measurement of Lateral Erosion at Proposed River Crossing 

 Sites of the Alaska Pipeline. U.S. Geological Survey. Water Resources 

 Division. Alaska District. 39 pp. 



Chow, V. T. 1959. Open-Channel Hydraulics. McGraw-Hill Book Company, New 

 York. 680 pp. 



Doyle, P. F., and J. M. Childers. 1976. Channel Erosion Surveys Along TAPS 

 Route, Alaska, 1976. Open-File Repor t-77-l 70 (Basic Data). U.S. Geolog- 

 ical Survey. Anchorage, Alaska. 90 pp. 



Lamke, R. 0. 1979. Flood Characteristics of Alaskan Streams. Water Resources 

 Investigations 78-129. U.S. Geological Survey. Anchorage, Alaska. 61 pp. 



104 



