SPDSS_Task66-2_CollectDevelopMunicipalIndustrialConsumptiveUseEstimates

• Title: SPDSS Task 66.2 - Collect and Develop Municipal and Industrial Consumptive Use Estimates
• Description: This memorandum presents the general approach used to develop municipal and industrial consumptive use for the CU and Losses Summary Report and estimate indoor and outdoor water demands, consumptive use, and return flows for SPDSS modeling efforts.
• Decision Support - Doc Type: Task Memorandum
• Date: 11/14/2007
• DSS Category: Consumptive Use
• DSS: South Platte
• Basin: South Platte
• Contract/PO #: C153954
• 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

3. Historical Municipal and Industrial Consumptive Use
Consumptive uses associated with municipal water user demands and self-supplied industrial
water demands were estimated based on CU rates associated with the demands over the SPDSS
study period, as summarized below. Municipal consumptive use is estimated based on CU rates
for in-house and outside uses applied to the in-house and outside demands. Self-supplied
industrial consumptive use is estimated based on SSI demands and user-supplied CU rates or
decreed CU rates, depending on the industry analyzed.
Municipal Water users Consumptive Ilse
In House Consumptive Use
Consumptive use rates for municipal systems connected to central waste water treatment systems
are generally accounted for as 5 percent of the in-house water demand. Consumptive use rates
for municipal systems treated by individual septic disposal systems are generally accounted for
as 10 percent of the in-house water demand. Specific types of waste water treatment for
individual municipalities were not researched for the Task 66 effort. Nevertheless, it is
recommended that municipal CU rates be estimated at 5 percent based on central sewer treatment
for municipalities identified in the population data. Similarly, CU rates for unincorporated
population are estimated at 10 percent based on septic waste water treatment. This methodology
is considered appropriate for planning purposes.
Outside Consumptive Use
Consumptive use and return flows from outside demands associated with municipal water use
are not quantified by all municipalities within the SPDSS study area. The methods used to
quantify municipal outside CU rates and amount and location of lawn irrigation return flows
(LIRFs) were gathered through the Task 5 interviews and additional information collected from
engineers and water providers in the SPDSS study area.
Municipalities have primarily relied on the Cottonwood Curve method as the means for
calculating the annual amount of LIRFs and associated CU for outside deliveries. The
Cottonwood Curve method was developed from a lysimeter study by W.W. Wheeler and
Associates in support of the Cottonwood Water and Sanitation District's plan for augmentation
(Case No. 81CW142). The Cottonwood Curve defines the CU rates for outside uses based on the
relationship between return flow amounts as a percent of total application; and total application
as a percent of the potential consumptive use, as shown in Figure 5. The Cottonwood Curve
method acknowledges that homeowners and business owners do not typically irrigate according
to the exact demands of the crop, and therefore some level of return flows occur even if full
irrigation requirements are not met (see return flow amounts in Figure 5 for X-values less than
100 percent). The Cottonwood Curve is generally considered to be the most technically
acceptable methodology for quantifying LIRFs in the South Platte River basin.
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