CRDSS_Task1_15-17_ColoRiver_IrrigationReturnPatterns

• Title: CRDSS Task 1.15-17 Colorado River Basin Representative Irrigation Return Flow Patterns
• Description: The purpose of this task was to develop return flow patterns for both the monthly and daily CRDSS planning models using geologic parameters representative of actual locations of irrigated acreage in each of the five CRDSS basins and a methodology that is acceptable and can be reproduced.
• Decision Support - Doc Type: Task Memorandum
• Date: 1/20/2003
• DSS Category: Surface Water
• DSS: Colorado River
• Basin: Colorado Mainstem
• Contract/PO #: C153933, C154062
• Grant Type: Non-Reimbursable
• Bill Number: SB92-87, HB93-1273, SB94-029, HB95-1155, SB96-153, HB97-008
• Prepared By: Leonard Rice Engineering

Approach
The analysis performed using the State's model requires the following Glover parameter inputs:
T =Transmissivity in gallons per day per foot (gpd/ft). Transmissivity is the product of
hydraulic conductivity (K) in feet per day, saturated thickness (b) in feet, and the
appropriate conversion factor.
S =Specific Yield as a fraction
W =Distance from stream to impervious boundary in feet (ft)
x =Distance from point of recharge to stream in feet (ft)
Q =Recharge Rate in gallons per minute (gpm)
For a monthly analysis, the alluvial aquifer is "stressed" for one month (i.e. a unit of recharge is
applied for one month) and the amount of accretion to the river is estimated for that month and
subsequent months, until 100 percent of the recharge reaches the river. For a daily analysis, the
aquifer is "stressed" for one day, and the amount of accretion is estimated for that day and
subsequent days, until 100 percent of the recharge reaches the river.
The following approach was followed to estimate representative model parameters for western
slope alluvial aquifers.
1. Choose locations in each of the western slope basins that provide a representative sample of
lands irrigated from mainstem and tributary streams.
2. Use available geologic data from the State Engineers Office records or from geologic
mapping to determine appropriate parameters required for Glover analyses.
3. Based on the individual site values, determine average values for each Glover parameter to
use in an overall western slope analyses.
4. Determine the appropriate distance from irrigated lands to live stream (value "x") to use in
estimating the Glover depletion factors for lands relatively close and lands further from the
stream.
After representative parameters were selected, two monthly and two daily glover analyses were
performed using the State's model, representing lands irrigating relatively close and lands further
from the stream. The analyses resulted in monthly and daily accretions to the river due to
recharge through the alluvial aquifer.
The original CRDSS return flow patterns also included returns from surface runoff. Although
not discussed in the CRDSS Memo 1.15-17, the Daily Yampa Memo estimated that 50 percent
of total returns were from surface runoff and occurred during the same month as diversion for the
monthly analyses. For the daily analyses, surface runoff was estimated to reach the river the day
after diversion. The recharge factors from the Glover analyses were revised to include surface
water runoff and formatted for use in the Statemod Delay Pattern file (*.dly).
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