Immediately after its construction , the reservoir began to suffer from heavy sedimentation , a problem made worse by occasional wildfires in upstream areas . In 1932-33 wildfires burned some of the drainage basin , and in response to the increased erosion the U.S. Forest Service constructed two debris dams upstream to hold back sediment washed off the burned landscape . The Mono Debris Dam , an Ambursen-type structure , was built in 1936 and had completely filled with 1 million yd3 ( 770,000 m3 ) of sediment by 1938 . The concrete-arch Agua Caliente Debris Dam was completed in late 1937 and by 1941 had filled with 750,000 yd3 ( 570,000 m3 ) of sediment . Despite the scale of these conservation projects , they only extended Gibraltar 's useful life by a few years . The flood of March 1938 was a major contributor to the large volume of debris run-off and caused $ 340,000 of damage downstream in the Lompoc area
flood of March 1938
Los Angeles flood of 1938
Gibraltar Dam