V. Water Use

This section provides a general description of water use within the District for municipal and agricultural purposes.

A. LAND USE

Water use in the District is a function of land use and relative wetness within a given year. Land use with respect to agriculture is influenced by the economics of a particular crops and in response to "dry" winters as well as "wet" winters and springs.

Available land use information has been compiled by DWR. Land use surveys have been completed by DWR for the years of 1961, 1973, 1976, 1981, and 1989. Also, in April 1999, DWR completed compilation of its 1998 land use survey for Yolo County. This information will be available in electronic format, however, it was not available in time to incorporate into this document.

A summary of land use within the District in 1981 and 1989, upstream and downstream of the District's Capay Diversion Dam, is presented on Table 4 and Table 5. For comparative purposes, a summary of agricultural land use is shown on Table 6 for the District and Yolo County. As shown, in 1989, irrigated land in the District represented approximately 40 percent of the total for Yolo County.

Presented on Table 7, is a summary of urban land use within the District and Yolo County in 1989. As shown, urban land within the District represents nearly 63 percent of the total urban land in Yolo County.

(acres)

¹Estimates of riparian vegetation are available through the Yolo County Planning Department.

Source: California Department of Water Resources.

(acres)

Source: DWR Land Use Survey.

Location	Area, acres	Area, percent
Within District	16,629	62.7
All of Yolo County	26,544	100.0

1. Land Use Planning

The District has no authority or responsibility regarding land use planning. This is the responsibility of the county and cities. Accordingly, it is the responsibility of the county and cities to assess existing and proposed land uses from the standpoint of land use impacts on groundwater supplies and contamination. The District reviews proposals for changes in land use and offers comments relative water use, flood control, and drainage to the county and cities in Lake and Yolo counties.

B. WATER USE

1. Agricultural

DWR, in its compilation of land use for 1989, also identified the source of water for irrigating individual fields. The fields were identified as being irrigated with surface water, groundwater, and both surface water and groundwater. Presented on Table 6, is a summary of land use and source of water. Inspection of Table 8 shows that the land irrigated with surface water and groundwater within the District is nearly 50-50. In years when the District has little or no surface water available, virtually all irrigation will be with groundwater supplies. For Yolo County as a whole, only about 36 percent of the land is irrigated with groundwater (Table 9).

>Using the land use information presented by DWR for 1976, 1981, and 1989, an estimate of water use was made. Water use for the years of 1976 and 1989 was treated as dry years, and 1981 as an average year. The difference between wet and dry hydrologic conditions is in the amount of rainfall effectively available to meet the crop consumptive use. Presented on Table 10, is a summary of the estimated total water use for irrigation in Yolo County and the District for the three years noted above. The unit water use for the same three years is presented on Table 11. Based upon the figures presented on

	Source of Irrigation Water
Land Use	Groundwater Only	Surface Water Only	Surface Water and Groundwater1
Agriculture Grain	18,429	19,525	7,267
Rice	31	357	315
Field	6,053	9,830	2,428
Pasture	6,404	9,901	2,665
Truck	9,707	9,362	10,753
Orchard	7,690	4,039	1,677
Fruits	52	57	0
Vineyard	391	248	0
Fallow	3,531	3,363	56
Intercropped	373	245	0
Double Cropped	433	408	561
Subtotal	53,094	57,335	25,722
Semi-agricultural	3,422	3,949	125
TOTAL	56,536	61,284	25,847

¹ Land using surface water and groundwater.

Source: DWR Land Use Survey.

	Source of Irrigation Water
	Groundwater		Surface Water		Surface Water and Groundwater1
Location	area	percent	area	percent	area	percent
Within District	56,536	53.2	61,284	32.2	25,847	70.5
All of Yolo County	106,350	100.0	190,600	100.0	36,675	100.0

¹Land using surface water and groundwater.

	Yolo County		District
Year	Irrigation Application Total, ac-ft	Return Flow2 Total, ac-ft	Irrigation Application Total, ac-ft	Return Flow Total, ac-ft
1976	1,025,000	279,000	381,000	101,700
1981	954,000	276,000	341,500	98,200
1989	1,019,000	276,000	377,600	100,900

¹Based upon crop acreage compiled in DWR's respective land use surveys.

²Return flow is applied irrigation water that percolates below the crop root zone and enters to the groundwater basin or flows from the farm field into a drain and is recovered or recoverable for irrigation on a downstream field.

	Yolo County		District
Year	Irrigation Application Total, ft	Return Flow2 Total, ft	Irrigation Application Total, ft	Return Flow Total, ft
1976	3.29	.87	2.97	.79
1981	3.00	.87	2.67	.77
1989	3.22	.87	2.91	.78

¹Based upon crop acreage compiled in DWR's respective land use surveys.

²Return flow is applied irrigation water that percolates below the crop root zone and enters the groundwater basin or flows from the farm field into a drain and is recovered or recoverable for irrigation on a downstream field.

Table 10, the amount of water applied for irrigation within the District represents approximately 37 percent of the total water applied for agriculture in Yolo County.

2. Urban

Urban water use within the District is largely within the cities of Davis, Woodland, and Winters, and UCD although there is urban-type water use within the communities of Esparto, Madison, Capay, and others in the Capay Valley. Presented on Table 12, is the estimated urban water use within the District and West Sacramento, which is the principal urban area in Yolo County outside of the District. As shown on Table 12, 75 percent of the water use in Yolo County occurs within the District. All of the urban demand within the District is provided from groundwater.

C. WATER USE EFFICIENCY

Water use efficiency is addressed below from the standpoint of the District as a system and at the farm level.

1. System Efficiency

Essentially all water delivered by the District for irrigation is diverted along Cache Creek in Capay Valley and at the District's Capay Diversion Dam. Operational spills occur at the District's Capay Diversion Dam and within the District's water delivery system. Operational spills that occur at Capay Dam in the summer will generally percolate to the groundwater basin before reaching Interstate 505. Operational spills that occur along the District's distribution system discharge into sloughs or drains and are recovered and reused by the District and individual landowners.

Estimates 1996 from Water Resources Association, Water Resources Management Committee, 1996.

The water diverted into the District discharges as surface flow through Cache Creek and the Willow Slough Bypass and as subsurface flow under Putah Creek into Solano County.

With respect to surface water, water flowing out of the District through Cache Creek, or the Willow Slough Bypass, water flowing in Cache Creek during the summer months is agricultural return flow that enters Cache Creek as surface drainage, subsurface flow, or a combination of both. The boron concentration of this water in Cache Creek is generally high (3 ppm or greater) as measured by the District at the Moore Canal Siphon. As the water is "resurfacing" groundwater, it represents the quality of the shallow groundwater in the vicinity of Cache Creek. Water flowing out of the District via the Willow Slough or North Davis Drain, on visual observations, is small. Although readings of a stream gage at the County Road 102 Bridge were recorded at one time, currently no data is being gathered for the Willow Slough.

With respect to groundwater flowing out of the District, the delivery of water by the Solano Irrigation District (SID) since the early 1960s, has served to alter groundwater gradients near Putah Creek. Prior to SID's delivery of water from the Solano Project, the groundwater gradients in the vicinity of Winters were in a south easterly direction. The delivery of water by SID relieved the overdraft that was occurring in Solano County, thereby significantly raising groundwater levels. The result was beneficial for Yolo County in that the groundwater gradients now tend to flow in a more easterly direction towards Davis. Groundwater pumping by Davis, Woodland, and the intervening agricultural areas have reversed the historic west to east gradient, thereby curtailing the subsurface flow out of the District along its eastern boundary.

In summary, although not quantified, the amount of water leaving the District is small and that which flows out via Cache Creek is high in boron. Thus, as a system, the efficiency of water use within the District is judged to be high, although undocumented.

2. On-farm Efficiency

Both the NRCS and RCD are engaged with the farming community in programs to improve irrigation efficiencies, manage water quality impacts, reduce field and channel erosion, and restore wildlife habitat. Land-leveling to improve irrigation and farm efficiencies is extensive as well. The construction of tailwater recovery systems through the RCD's Model Farm Program is successful and requests for assistance exceeds available resources. As noted in a previous section, the District participates with in-kind services to support this program. Although there is a great deal of activity aimed at improved water management at the farm level, information to quantify it is extremely limited.

D. SUMMARY

In the future, water use within the District will be influenced most by cropping patterns and urban growth. Over the long term, the efficiency of use of water from the Cache Creek watershed can be increased by the following:

Increasing the capture of the "unmanaged" water flowing out of or through the District.

Increasing the use of the District's water supply, thereby increasing the magnitude of in-lieu groundwater recharge and incrementally reducing the amount of water flowing from Indian Valley Reservoir as a "flood spill."