Effects of vegetation on floods at four Arizona sites

Four examples show the effect of vegetation on stage, discharge or frequency of floods. An 8-year growth of trees on the streambed at site 1 increased channel roughness enough to cause the average water surface elevations that were computed for 10-year and 100-year floods to be 0.49 and 0.91 meters higher than those for a channel without vegetation. A 6-year growth of vegetation and sediment deposition formed 1.5-meter high flood terraces at site 2 and narrowed the channel from 55 meters to about 12 meters. Similar terrace development in 18 years narrowed the channel at site 3 from 139 meters to an average width of 24 meters. At a stage where the channel carried 716 cubic meters per second in 1952, it carried 227 cubic meters per second in 1970. Additional aspects of the subject are discussed.