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SPDSS_Task64_ReviewDevelopPrecipitationRechargeEstimates
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Last modified
4/17/2013 9:36:20 AM
Creation date
6/11/2008 2:20:57 PM
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Decision Support Systems
Title
SPDSS Task 64 - Review and Develop Precipitation Recharge Estimates
Description
This memorandum presents the general approach used to develop monthly precipitation recharge estimates for both the Denver Basin and South Platte alluvial ground water models.
Decision Support - Doc Type
Task Memorandum
Date
5/11/2007
DSS Category
Groundwater
DSS
South Platte
Basin
South Platte
Contract/PO #
C153953
Grant Type
Non-Reimbursable
Bill Number
SB01-157, HB02-1152, SB03-110, HB04-1221, SB05-084, HB06-1313, SB07-122
Prepared By
Leonard Rice Engineering
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land conditions. Land use types of "pasture or range" and "straight row crop" with good <br />quality hydrologic conditions were selected to represent irrigated land conditions. <br />Curve numbers are adjusted based on soil types. Soil types for this analysis were selected <br />from the Hydrologic Group described in the Water Features Table in STATSGO. Curve <br />numbers are also adjusted based on the preceding 5-day antecedent moisture condition <br />(AMC). The NEH uses the following AMC levels (SCS, 1985), determined using the <br />ranges shown in Table 1 below: <br />AMGI. Lowest runoff potential. The watershed soils are dry enough for <br />satisfactory plowing or cultivation to take place. <br />AMC-H. The average condition. <br />AMC-III. Highest runoff potential. The watershed is practically saturated from <br />antecedent rains. <br />Table 1 <br />Seasonal Rainfall Limits for AMC <br />AMC G Total 5-Da Antecedent Rainfall inches <br />roup Dormant Season Growin Season <br />I Less than 0.5 Less than 1.4 <br />II 0.5 to 1.1 1.4 to 2.1 <br />III Over 1.1 Over 2.1 <br />AMC values were calculated from daily precipitation data and used to adjust the curve <br />numbers for the analysis of non-irrigated lands. An AMC of III (wettest condition) was <br />used for irrigated lands, to reflect that irrigation water is being applied. <br />2) Estimate Precipitation to ET (PE) and Soil Storage (Ps) on Irrigated Lands <br />During the Growing Season (April through October) <br />The surface water runoff was subtracted from the total precipitation (PT_P~. The <br />remaining precipitation was estimated to go to the following uses: (a) satisfy crop ET and <br />soil moisture reservoir storage and (b) deep percolation: <br />a. The SCS Effective Precipitation Method outlined in Technical Release 21 <br />(described in the SPDSS memorandum for Task 61 -Effective Precipitation <br />Estimates for Determining Crop Irrigation Water Requirements) was used to <br />estimate the component of precipitation that directly satisfies ET on a monthly <br />time step. Consistent with accepted engineering analyses, this monthly approach <br />considers precipitation that may be held in soil moisture storage and made <br />available for subsequent use by the crops (PE + Ps). <br />b. Equation 1 was used to calculate deep percolation (P~). <br />Root zone depths of 3.3 feet and 4.9 feet were used to represent irrigated row-crop and <br />irrigated alfalfa (corresponding to root zone depth recommendations in ASCE Manual <br />70). <br />Task 64.doc 9 of 13 <br />
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