39. The natural vegetative coverage of the Pacific region varies from the coast redwood forests to spiney cacti of the alkaline deserts. In the interior mountainous area, forests clothe the mountains in response to 20 inches and more of rainfall. Grasses and open woodland cover the foothills, mesas, and the valley plains, where rainfall varies from 25 to 8 inches. Scant vegetation marks the desert areas of still less rainfall. In the first two vegetative zones the coverage of vegetation was once sufficient on most of the area to hold soil in place and deliver such water as ran off reasonably free from silt and debris. Man and his animals have upset this balance between vegetation, soil formation, surface erosion, and run-off by increased fires, destructive logging, overgrazing, cultivation of mountain slopes, faulty drainage in road construction and in other ways. This has increased runoff from heavy rains and, through erosion of slope soils, has increased sediment carried by flash floods. Woodland, grassland, and brushland areas of the foothills and mesas are regions of most delicate balance on which acceleration of erosion and run-off has become most serious.

40. A remarkable change has taken place in the regimen of intermittent streams in the West in the past 50 years. In their original condition the mountain valleys of the Pacific drainages were generally covered with broad grassy flats. An especially dense grassy growth marked the annual spread of flood waters. Flashy flood flows from adjacent slopes spread in thin sheets through these grassy flats and the reduction in flood velocities caused deposit of silts, adding year by year to these alluvial fills. Marshy and intermittent lakes often occurred in these valley floors. Such flats furnished wild hay and splendid grazing for the herds of the first stockmen. Drainage slowly found its way through these grassy flats in willow-bound channels. These alluvial fills of fertile soils when irrigation water was available furnished sites for agricultural development.

41. Rarely were there any gullies cutting into these alluvial fills on the advent of the white man. Since that time, however, gullies have appeared in nearly every valley of the arid and semiarid sections; they are becoming young canyons, through which torrential flood flows cut and carry enormous burdens of silt. Water tables in the valley alluvium have dropped and have changed the character of vegetation. These valley fills of the West contain millions of acre-feet of alluvium which is in the process of being moved out and threatens many reservoirs that are or may be built in these regions. Such is the menace to the irrigated west.

42. The solution of these problems involves restoration, protection, and management of the forest and range cover, and special engineering features to satisfactorily safeguard water supply.

43. Forest-land management in the Pacific region involves 179,896,000 acres of forest land, supporting 1,041,628 million board feet of commercial timber. It comprises the last great area of virgin timber growth and is of very great value in the economic and social development of the Pacific region, as well as the Nation as a whole. These forests also are valuable for range forage production, recreation, wildlife, and other miscellaneous resources. Except in the Pacific Northwest, watershed values are generally dominant, since water is the product of highest value from the mountains. Watershed values have been recognized by the legislation, appropriations, and Federal

policy governing the establishment, administration, and protection of the 106 million acres within national forests and, in the main, watershed conditions are improving under timber and range management being applied. These values have also been recognized in other acts providing for Federal cooperation with States and other agencies in fire protection and reforestation.

44. The forest land of the Pacific region has been classified as 117,074,000 acres having major watershed protective value, as 52,275,000 moderate, and as 10,547,000 slight. Included within the major classification are most of the coniferous forest stands on the headwaters of the streams at the higher elevations where the cover retards snow melt, facilitates absorption of rain and snow water, and unless destroyed controls accelerated soil erosion. Included also are woodland areas at lower elevations where if vegetation is depleted abnormal soil erosion is or will be disastrous in irrigation and community development. (See accompanying map.)

45. The forest watershed-protection problem in the west is chiefly that of the 19,500,000 acres within the unregulated public domain and of the 56 million acres of private lands. Destructive logging, repeated fires, and overgrazing have seriously impaired the watershed values of these lands. Timber has often been replaced with brush; the herbaceous plants, so important in erosion control, have in places been reduced 50 to 80 percent. The situation on private lands is such that it is believed the public will need to acquire for reforestation some 32 million acres for watershed protection purposes, at a cost of about $150,000,000. Critical areas which will not restock naturally should be planted. On lands remaining in private ownership the regulatory provisions of the forest industry codes under the National Industrial Recovery Act are expected to greatly facilitate improved fire protection and management. It is desirable that these regulatory provisions be made permanent.

46. Range management of the extensive brushlands and grasslands lying below the forested zones is necessary to prevent damaging overgrazing. Most of these lands are in unregulated public domain and intermingled private holdings. Palatable grasses and herbs have been eaten into the ground, producing conditions which have been detrimental to the livestock industry and to irrigation interests. Carrying capacities of the range have been seriously reduced and accelerated soil erosion, storm run-off, and gully cutting have added to silting of reservoirs. Rehabilitation by regulation of grazing use and artificial revegetation of these extensive areas is required as a part of the gram for stabilization of watershed conditions. Improvement of these conditions on the public domain rests upon prompt enactment of legislation.

pro

47. Engineering works are required to halt the accelerated erosion and to supplement revegetation and range management. These measures will include flood-detention dams, check dams, waterspreading works, and barrier systems for debris control.

48. In any program for development of the highest sustained uses of waters of the West, particularly of the more arid section, full attention to conditions of the watershed slopes is required to safeguard developments by the prevention and control of accelerated erosion, and in some cases to reduce the rate of the normal geologic processes of erosion. The watersheds yielding the water supplies

become an integral part of any development in the use of these western waters. Interests receiving benefits from watershed control should contribute to the cost thereof.

SACRAMENTO AND SAN JOAQUIN RIVERS, CALIF.

The introduction contains a general discussion of the problems of the utilization of the water resources of the Pacific region as a whole, and should be considered in connection with the chapter on the Sacramento and San Joaquin Rivers.

I. INTRODUCTION

1. General description.—The drainage basins of the Sacramento and San Joaquin Rivers form the Central Valley of California, which lies between the Sierra Nevada Mountains and the Coast Range and drains through the break in the Coast Range at San Francisco Bay. The valley floor is a flat alluvial plain over 400 miles long and 30 miles wide. The Sacramento River rises in northern California and flows about 320 miles in a southerly direction to its mouth at the eastern end of Suisun Bay at Collinsville. Its total area is about 27,100 square miles. The San Joaquin River rises in the Sierra Nevada Mountains in central California, and flows southwesterly to the vicinity of Mendota and thence northwesterly to Suisun Bay, which it enters just south of the mouth of the Sacramento River. Its total length is about 325 miles and its drainage area, exclusive of the Tulare Basin, is about 18,000 square miles. Tulare Basin is formed by a ridge across the valley floor north of the Kings River and has a drainage area of about 14,500 square miles, including that of the Kern River. During very wet seasons the waters of this basin flow over this ridge into the San Joaquin Basin. The Kern River rises in the Sierra Nevada Mountains south of the headwaters of the San Joaquin, and flows in a general southwesterly direction for about 150 miles, emptying into the reservoir which occupies the northern end of what was formerly Buena Vista Lake. The total low water flow is diverted for irrigation in the lower reaches and only the return flow and the flood waters reach the reservoir. At the mouths of the Sacramento and San Joaquin Rivers there is an extensive delta region of rich agricultural land reclaimed from the original marshes.

2. Development in Great Central Valley Basin.—The total population of the basin is about 882,000 or 15 percent of that of the entire State. Sacramento, population 93,685; Fresno, 52,558; Stockton, 47,951; Bakersfield, 26,179, and Modesto, 13,847, are the principal cities. Approximately 12,500,000 acres are in farms and the normal annual value of farm products is about $310,000,000. Mineral production, including oil and gas, amounts to approximately $73,000,000 annually, and the value of manufactured products is about $265,000,000. The valley is well served by railroads and highways and by water carriers on the lower Sacramento and San Joaquin Rivers. Hydroelectric power is highly developed in the mountain areas, and natural gas is available for cheap fuel for steam power where needed.

3. Precipitation and run-off.-The summers are long and hot, with practically no rain. The winters are short and mild, with frequent rains and practically no snow except in the mountains. The average

annual precipitation, including mountain areas, is about 42 inches in the northern portion of the basin and 23 inches in the southern. On the valley floor it varies from 4 to 25 inches. Seasonal variations are large, with dry years usually occurring in cycles. For the period 1889-1929, the mean annual run-off of the Sacramento Valley streams was about 25,000,000 acre-feet, and of the San Joaquin, Tulare Basin, and Kern Rivers, about 12,000,000 acre-feet. Most of the run-off occurs from December to March.

II. DISCUSSION OF PROBLEMS

4. Major problems of improvement. The principal problems which must be faced in any general plan of improvement for the basin are concerned with the conservation, distribution, and utilization of water. The easily developed irrigation waters of the Central Valley are now practically all in use and large areas in the southern part deriving their supply from underground sources are facing a water famine through overdraft. Summer stream flow has become inadequate while large unregulated winter flows are wasted. Storage of the winter flows of streams of the Sacramento Basin would benefit irrigation, navigation, flood control, and power development and permit transfer of excess water from the north to the south. The broad solution of the problem generally agreed upon is that the streams in the mountainous regions should be set aside for the development of hydroelectric power and placer mining, which will not conflict with the re-use of water below; that the main streams should be regulated so as to secure the maximum beneficial uses of the water for all purposes by means of foothill reservoirs; that provision should be made for the transportation of Sacramento River water, in excess of local needs, to the San Joaquin Valley; and that the comprehensive program should be developed step by step as the needs justify. To give a better understanding of the problems, they are discussed individually in succeeding paragraphs.

5. Municipal water supply. The cities clustering on San Francisco Bay have had to extend their water systems to the Sierra Mountains to secure adequate fresh water supplies. Other communities may be expected to seek additional supplies as their local supplies become inadequate or unsatisfactory for use. Such uses for water must take precedence over all others in any plan for water conservation. With the exception of the proposed conduits from the delta to areas north and south of Suisun Bay, constructed as a phase of salinity control, there is no project for municipal water supply included in the general plan for water conservation.

6. Irrigation-Existing situation.-The areas of land under irrigation in the different sections of the basin are approximately as follows:

In dry years, irrigation of lands in the Sacramento and the North San Joaquin Valleys utilizes all of the low-water flows of most of the streams without securing an adequate supply. This results in inade