VI. District's Water Delivery System

This section provides a general description of the District's water delivery system.

A. GENERAL

The District's water delivery system consists of the Capay Diversion Dam on Cache Creek and the extensive network of canals and laterals served from the District's two main canals, the Winters Canal and West Adams Canal. The headworks for each is an integral part of the Capay Diversion Dam. In total, the District's system includes over 175 miles of irrigation and drainage facilities.

The major portion of the District's water delivery system is earthen or unlined channels. The uppermost reaches of the Moore Canal, the Winters Canal, and the West Adams Canal are lined with concrete.

B. EFFICIENCY

The District operates and maintains an extensive conveyance and distribution system comprised of earthen canals. Losses from this system, as seepage and evaporation, vary from year to year, but has ranged from 15 to 65 percent from 1970 to 1996 (Table 13). The greatest part of the losses is the result of seepage and percolation along the canals and laterals. It is important to note, however, that the major part of these losses are recoverable from the groundwater basin.

Over the years, various parties have suggested that the District should concrete-line its water delivery system to minimize seepage losses. From the standpoint of managing the water supply available from the Cache Creek system, lining the District's water delivery system is not deemed to be a prudent water management measure.

TABLE 13

YOLO COUNTY FLOOD CONTROL

WATER CONSERVATION DISTRICT

WATER MANAGEMENT PLAN

SUMMARY OF DISTRICT WATER SERVICE OPERATIONS: 1970-1996¹

amount, ac-ft

Year	Diverted	Sold	Difference, %2
1970	126,532	101,100	20.10
1971	157,013	112,133	28.58
1972	77,428	53,309	31.15
1973	144,215	110,645	23.28
1974	136,201	110,767	18.67
1975	138,498	117,257	15.34
1976	104,114	74,279	28.66
1977	0	167	N/A
1978	162,898	109,372	32.86
1979	173,269	127,144	26.62
1980	155,625	109,782	29.46
1981	185,396	139,890	24.55
1982	159,561	120,617	24.41
1983	117,239	78,906	32.70
1984	194,963	146,335	24.94
1985	180,835	135,343	25.16
1986	147,510	107,320	27.25
1987	190,576	141,594	25.70
1988	184,738	133,158	27.92
1989	143,882	79,829	44.52
1990	0	0	N/A
1991	95,180	32,540	65.81
1992	63,738	25,339	60.25
1993	149,598	106,197	29.01
1994	131,948	82,119	37.76
1995	151,846	119,655	21.20
1996	169,477	132,262	21.96

¹Below Capay Diversion Dam.

²The difference represents canal seepage, evaporation, and tailwater flowing from the District.

With the current demand on the District's water supply system, the lining of canals and laterals would result in more water stored in Indian Valley Reservoir, thereby increasing flood releases from the reservoir. At the same time, it would eliminate an increment of groundwater recharge. From a water management standpoint, only when the demand on the District's water supply system has increased to the point where flood releases were nearly eliminated should the lining of canals and laterals be considered. At that time, the economics of lining canals and laterals in relation to the cost of pumping groundwater would have to be evaluated.

C. OPERATION

The District's water delivery system is operated as a "demand" system, as opposed to a "rotation" system. This manner of operation is the most efficient in terms of water management. The District delivers water at the request of the farmers. Thus, water is delivered when it is needed. This type of operation facilitates the most efficient use of water for irrigation.

Also, water that may flow past the end of a canal or lateral may be retrieved in a downstream section of the District's system or sold in a downstream slough. The same is true of tailwater from farm fields. Excess applied irrigation water that does not percolate and runs off the end of a farm field is recovered and reused. Thus, very little water of suitable quality leaves the District.