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.he larger water-transported rock debris is [leposited on the cone. The discharge of the stream is also reduced in the course of its travel down the cone as water seeps into the permeable' bed material. From the base of the cone the stream crosses the valley floor to empty into the ocean. When southern California was first settled, channels on the cones and in the alluvial valleys were often poorly defined and semipermanent, and during periods of flood, the waters spread over wide flood plains. r The rapid growth of California changed conditions. On thousands of acres of alluvial cones, old river bottoms, and flood plains, where floodnows once ran relatively unconfined, there are now homes, orchards, highways, railroads, towns, and cities. The development has created a complicated, if not unique, flood problem. Flood hazards now are not confined to water runoff alone but inelude debris that is brought down the steep mountain slopes and is deposited on streets and developed property. To some .xtent the problem has been aggravated by ncreased runoff and erosion in mountain areas where erodible soils have been laid bare as a result of forest and brush fires of both natural and manmade origin. I, I 'l A permanent solution to the problem is a difficult one. Geologically speaking, the mountains are young and break down rapidly under the combined action of the elements. Rcservoirs and debris basins fill with sediment and rapidly lose their useful capacity. Storm rainfall is often excessive and even such tremendous floods as those of January 1916, January 1934, March 1938, and January 1969 may not be indicative of the maximum nood potential. For example, the storm of January 21-23, 1943, was the most intense of record in much of the region from a standpoint of nood-producing potential. However, nooding was not disastrous in 1943 because the rains fen on dry ground that absorbed much of the rainfall. There is no doubt that despite the application of our most advanced hydrologic .rinciples and nood-control practices, all element of risk still exists for those who occupy natural flood channels, nood plains, and alluvial cones. However, without application of those principles and practices, such occupancies are virtually an invitation to future disaster. Social and economic considerations compound the nood problems associated with the physical environment. The region has been growing at a tremendous rate. For example, in 1935 the population of greater Los Angeles was about 2.5 million; it is now about 7 million and is still increasing. The pressure to provide building sites to house the increasing population and attendant industrial and commercial activity places a great burden on city and county planners. Furthermore, no direct central planning authority exists for the heavily urbanized areas because local jurisdiction over planning resides in the many incorporated communities. The local planning, although often based on regional concepts, is not uniform in quality. The number of municipalities has also been increasing over the years. Using the Los Angeles area again as an example, the number of incorporated areas in Los Angeles County increased by 75 percent between 1935 and the present (1969) from 44 to 78. Many of these municipalities are contiguous and form a continuous urban sprawl. The difficulty of planning on a regional scale to provide a logical pattern of zoning to protect residents from the hazards associated with storm and flood is apparent. FLOOD-CONTROL FACILITIES IN SOUTHERN CALIFORNIA Local organizations, cities, counties, the State, and the Federal Government have been, and are, attempting to remedy the hazardous nood situation through the following measures: I. The construction of reservoirs designed to store as much of the flood waters as possible. 2. The construction of debris basins to catch debris and sediment that otherwise would be deposited on the alluvial cones and valley noors. B3