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Eastern San Joaquin Groundwater Basin Groundwater Management Plan
<br />Northeastern San Joaquin County Section 2
<br />Groundwater Banking Authority 75 Hydrogeology
<br />The estimated and projected water demands presented are based on the following
<br />assumptions:
<br />1. Drastic changes in cropping patterns will not change drastically.
<br />2. Applied water demands include evapotranspiration, system losses, tailwater drainage,
<br />and percolation to groundwater.
<br />3. Applied water demands do not include conveyance losses or off-farm demands. The
<br />applied water demand is the information necessary for the groundwater model, which
<br />also takes into account the differences in consumptive use for each parcel of land.
<br />Urban areas have different consumptive use than agricultural areas, and consumptive
<br />use also varies between different types of crops. Therefore, the applied water demand
<br />will usually be less than the diversion amounts maintained by each district.
<br />The decrease of 132,000 af of agricultural water use can be compared to an increase in urban
<br />water use of 146,000 af. In terms of net demand, this is not a significant change. This similarity
<br />in demand is due to an approximate one-to-one conversion rate between urban and agricultural
<br />use for each acre. The usage rates for agricultural and urban water use are similar, with urban
<br />water use slightly higher per acre. Most land around urban areas is currently farmed; thus, in
<br />order for the urban areas to expand, agricultural land would be converted at an approximate
<br />one-to-one ratio. Because each acre of new urban land results in 1 less acre of agricultural
<br />land, and the water use figures are similar, the water demands are projected to remain
<br />essentially constant throughout the planning period.
<br />Table 2-4 Future Urban Water Demands
<br />City
<br />“1996”
<br />Current
<br />Demand3
<br />(af)
<br />Current Land
<br />Use (acres)
<br />Water Use/
<br />Acre4
<br />(af/ac)
<br />Future Land
<br />Use (acres)
<br />Future
<br />Demand (af)
<br />Net Increase
<br />in Demand
<br />(af)
<br />Escalon 1,400 932 1.5 2,106 3,200 1,800
<br />Lathrop 1 2,900 3,409 0.85 13,254 11,300 8,400
<br />Lodi 16,600 6,071 2.7 9,650 26,400 9,800
<br />Manteca 11,200 5,056 2.2 14,140 31,300 20,100
<br />Ripon 3,500 1,764 2.0 6,676 13,200 9,700
<br />Stockton 2 47,000 29,746 1.6 61,353 96,900 49,900
<br />Total 82,600 241,100 146,600
<br />Source: San Joaquin County Water Management Plan Volume I
<br />Notes:
<br />1. Lathrop water use per acre is lower than the remainder of the cities because their developments are less dense than
<br />other cities. The city’s future projections indicate that their water use per acre will increase to 1.4 ac-ft/ac. To maintain
<br />consistency, the water use per acre has been calculated as if it will stay the same over time. It is difficult to predict how
<br />development patterns will change, and the error that could be associated with this assumption is less than 0.5 percent
<br />of the future County demand.
<br />2. The demand for the city of Stockton only reflects the water use within city limits. Water providers for the Stockton area
<br />also provide significant water to the urban areas outside of the city limits. Total water deliveries for the Stockton urban
<br />area are approximately 62,000 ac-ft.
<br />3. Current year represents “1996”. Individual city water usage data is based on information gathered during the
<br />development of the San Joaquin County Water Management Plan, 2001.
<br />4. Water usage on a per acre basis is used to simulate groundwater withdrawals in the Camp Dresser & McKee
<br />developed DYNFLOW Groundwater Model for Eastern San Joaquin County.
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