BOARD00165 ‎(2)‎

• Board Meeting Date: 5/22/2007
• Description: OWCDP Section - Presentation by Leonard Rice Engineers - Holistic Approach to Sustainable Water Mgmt in NW Douglas Cty
• Board Meetings - Doc Type: Memo

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Holistic Approach to Sustainable Water Management in Northwest Douglas County
page 1

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EXECUTIVE SUMMARY

Coloradoans recognize that our long-term economic health hinges on the availability of adequate,
clean, reliable water supplies. As future demands for municipal, recreational, agricultural, and
industrial uses continue to increase throughout the state, providing adequate water supplies will
become more challenging. The water supply situation in northwest Douglas County serves as an
example of the challenge of providing an adequate municipal water supply. Current and future
residents are faced with a declining nonrenewable groundwater supply and limited options for
renewable water supplies. The recommendations in this report provide an innovative approach
toward balancing water supply and demand.

This study identifies two water management techniques that, particularly when paired together, offer
an overlooked renewable water supply alternative for Colorado: precipitation management through
rainwater and snowmelt harvesting and outdoor water demand management through use of water
efficient landscaping and irrigation practices. Rainwater harvesting is being practiced in at least
seven other western states.

The study objectives were to research existing studies and apply identified algorithms to show:

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· The potential of precipitation as a water supply,

· The potential water savings for a new residential development from outdoor water demand
management and the ability of rainwater harvesting to meet the demands for the three
landscape scenarios shown below, and

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Traditional

Moderate Conservation

Water Wise

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· The potential water savings from rainwater harvesting for existing developments that
currently rely on nontributary groundwater supplies.

Recommendations are made for ways to implement rainwater harvesting and protect existing water
rights through utilizing the legal framework of an augmentation plan.

Study Findings

1. The average annual yield from precipitation in northwest Douglas County is 17.5 inches and
the "sustainable", or dry year, yield is over 10 inches per year.

2. Only a portion of the total precipitation that falls on an undeveloped site returns to the stream
system through groundwater and surface water. At the study site, 100% of the annual
precipitation is lost to evapotranspiration (ET) and sublimation in a dry year. A maximum of
about 15% of the precipitation returns to the stream system in a wet year and on average,
around 3% returns to the stream through groundwater and surface water.

l~) Leonard Rice Engineers, Inc.

January 2007 - 1234CPN