3.5.1 Published Consumptive Use Coefficients
When available data to compute site-specific consumptive use coefficients are
insufficient, consumptive use is often estimated using published coefficients calculated by other studies conducted in regions with similar climates and water use
patterns [30]. This approach requires water withdrawal amounts categorized by
end-use type (e.g., domestic, commercial, irrigation) and the related coefficients.
The accuracy of this method is limited since the coefficients were originally
calculated for a specific set of use categories and are then applied uniformly
throughout the study area. Nonetheless, use of published coefficients does provide
estimates for planning purposes that would not otherwise be available.
For non-PWS use types, this study incorporates calculated consumptive use
coefficients available for three states in the Great Lakes region of the United States,
i.e., Indiana, Ohio, and Wisconsin [22]. This is the largest scale study conducted to
date in the United States that provides consumptive use coefficients at monthly time
scale. Shaffer [22] compiled available monthly withdrawal and return flow data for
water users in Ohio and withdrawal data for Indiana and Wisconsin for the years
1999–2004. Shaffer computed monthly and annual consumptive use coefficients
using the water balance equation, Eq. (1b), for the Ohio water users that provided
both withdrawal and return flow data. The dataset included 196 commercial
records, 471 industrial records, 289 thermoelectric power records, 59 golf course
records, 20 crop and 42 nursery irrigation user records, 18 livestock records,
33 aquaculture records, and 418 mining site records, where the number of records
refers to a facility and year in which both monthly withdrawal and return flow data
were available. This ICPRB study applies Shaffer’s monthly coefficients to withdrawal time series that do not have site-specific consumptive use coefficients in the
following use categories: AQU, COM, IND, IRR-GOLF, IRR-CROP, LIV, and
PP. Because mining withdrawals in the upper Potomac Basin are primarily for
dewatering purposes, consumptive use coefficients for the MIN use category are set
equal to zero. Consumptive use for PWS is calculated from upper Potomac Basin
data using methods described below.
3.5.2 Consumptive Use Estimates for PWS Systems
Shaffer [22] and others have noted that the simple water balance equation, expressed
by Eqs. (1a) and (1b), does not provide meaningful estimates of consumptive use
when used with withdrawal and discharge data from a public water supply system
and associated wastewater treatment system. Municipalities and counties distribute
potable water and collect wastewater via complex networks of pipes that are subject
to losses and gains not typically measured and difficult to quantify. Gains and losses
experienced by wastewater collection systems are particularly difficult to characterize because of the effects of inflow and infiltration (I/I). During wet weather periods,
inflows from direct connections to a wastewater collection system, such as rooftop
Interactive Geospatial Analysis Tool for Estimating Watershed-Scale. . .
151
When available data to compute site-specific consumptive use coefficients are
insufficient, consumptive use is often estimated using published coefficients calculated by other studies conducted in regions with similar climates and water use
patterns [30]. This approach requires water withdrawal amounts categorized by
end-use type (e.g., domestic, commercial, irrigation) and the related coefficients.
The accuracy of this method is limited since the coefficients were originally
calculated for a specific set of use categories and are then applied uniformly
throughout the study area. Nonetheless, use of published coefficients does provide
estimates for planning purposes that would not otherwise be available.
For non-PWS use types, this study incorporates calculated consumptive use
coefficients available for three states in the Great Lakes region of the United States,
i.e., Indiana, Ohio, and Wisconsin [22]. This is the largest scale study conducted to
date in the United States that provides consumptive use coefficients at monthly time
scale. Shaffer [22] compiled available monthly withdrawal and return flow data for
water users in Ohio and withdrawal data for Indiana and Wisconsin for the years
1999–2004. Shaffer computed monthly and annual consumptive use coefficients
using the water balance equation, Eq. (1b), for the Ohio water users that provided
both withdrawal and return flow data. The dataset included 196 commercial
records, 471 industrial records, 289 thermoelectric power records, 59 golf course
records, 20 crop and 42 nursery irrigation user records, 18 livestock records,
33 aquaculture records, and 418 mining site records, where the number of records
refers to a facility and year in which both monthly withdrawal and return flow data
were available. This ICPRB study applies Shaffer’s monthly coefficients to withdrawal time series that do not have site-specific consumptive use coefficients in the
following use categories: AQU, COM, IND, IRR-GOLF, IRR-CROP, LIV, and
PP. Because mining withdrawals in the upper Potomac Basin are primarily for
dewatering purposes, consumptive use coefficients for the MIN use category are set
equal to zero. Consumptive use for PWS is calculated from upper Potomac Basin
data using methods described below.
3.5.2 Consumptive Use Estimates for PWS Systems
Shaffer [22] and others have noted that the simple water balance equation, expressed
by Eqs. (1a) and (1b), does not provide meaningful estimates of consumptive use
when used with withdrawal and discharge data from a public water supply system
and associated wastewater treatment system. Municipalities and counties distribute
potable water and collect wastewater via complex networks of pipes that are subject
to losses and gains not typically measured and difficult to quantify. Gains and losses
experienced by wastewater collection systems are particularly difficult to characterize because of the effects of inflow and infiltration (I/I). During wet weather periods,
inflows from direct connections to a wastewater collection system, such as rooftop
Interactive Geospatial Analysis Tool for Estimating Watershed-Scale. . .
151