Arkansas Basin_Water Supply and Needs

• Basin Roundtable: Arkansas
• Title: Water Supply & Needs Report for the Arkansas Basin
• Date: 6/1/2006
• Author: CDM
• Basin Roundtables - Doc Type: Needs Assessment Documents

Section 5
Consumptive Water Needs in the Arkansas Basin
IJIII

baseline demand forecast should reflect future impacts of
conservation.

The M&I baseline water demand for each county was
adjusted by these percent savings factors to account for
the impact of Level 1 conservation savings. The resulting
estimate is used as the lowest conservation scenario
(Level 1 ).

5.1.1.6 Estimate of M&I CU Rates

Water use can be considered both in terms of gross
water needs - the total amount of water delivered to a
user - and in CU. Both are important considerations in
water planning. The difference between gross and CU is
the amount that is realized as return flows (i.e., through
wastewater treatment plants and lawn watering). CU is
generally higher in arid and semi-arid regions such as
Colorado, where more water is used for irrigation and
lost to evapotranspiration.

5.1.1.7 Arkansas Basin Existing Agricultural
Demands Method
Since the Arkansas Basin does not have a developed
Decision Support System (DSS) data set, quantification
and characterization of agricultural uses focused on
historic diversions, irrigated acreage, and crop type
distributions gathered from existing sources and studies.

For the Arkansas Basin, agricultural demands were
estimated using IWR values acre-feet per acre per year
(AF/AcNr) developed from the State of Colorado's HI
Model and irrigated acreages estimated from information
provided by CWCB, DWR, and the U.S. Department of
Agriculture (USDA) Census of Agriculture.

Summaries of the agricultural demand sources for the
Arkansas Basin is included in Table 5-4.

Table 5.4 A9.riCUltural oema.nd .I~f~rmation Sources

. a. . .
..a. ..a.la

! a ! a

Arkansas

HI Model, 1997-2000 HI Model 1950 - 2000
DWR, USDA
Census of
Agriculture

CDIVI

5-6

5.1.1.8 Arkansas Basin Future Agricultural
Demands Method

Future (2030) agricultural water requirements were
estimated by basin using annual average requirements
on a per acre basis, and projected future irrigated
acreage. The current requirements (AFY) are normalized
to the current irrigated acreages (AF/Ac/Yr) and
multiplied by the projected 2030 acreages to arrive at a
future total agricultural requirement (AFY). In other
words,

2030 Ag Irrigation Water Requirement (AFY) =
Current Average IWR Requirement (AF/Ac/Yr) x
Projected Irrigated lands (Ac) (5.2)

where

Current Average Requirement (AF/Ac/Yr) =
IWRlCurrent Irrigated lands (5.3)

2030 WSL CU; incidental losses, livestock watering, and
stock pond evaporation; and gross diversions were
estimated using the same approach (Equations 5.2 and
5.3). Projected WSL values represent anticipated crop
CU, assuming the ratio of available supply to irrigated
acreage stays the same. Incidental losses, livestock
watering, and stock pond evaporation represent
additional water consumption associated with the
projected irrigated acres. Gross diversions reflect the
anticipated amount of water actually diverted at the
stream to provide this level of combined CU. Basin
average annual diversions (averaged over the period of
record) were used in Equation 5.2 for these calculations.
Results are presented and discussed in Section 5.3.

Projecting future agricultural water demands includes an
evaluation of potential changes in irrigated acres, as well
as an estimate of agricultural water use per acre.

By 2030, reductions in irrigated acres are expected to
occur in most basins as agricultural lands are developed
for M&I use and/or water is transferred from agriculture
to M&I use to provide for M&I water needs. Additional
reductions in irrigated acreage in the Arkansas Basin
may occur if adequate augmentation sources are not
developed for the farms using alluvial groundwater as
their primary source of water supply.

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