Nuts and Bolts
Definitions
Equivalent Unit (EU): A unit of water use equal to one single-family residence. Based on current water system characteristics of permanent population and the commercial and part-time resident customers served by PAWSD, there are approximately 1.5 permanent residents per EU. EUs are the basis on which the water demand of all water users - commercial, residential and industrial - is defined. Also known in the water industry as Single Family Equivalent.
Acre-Foot (AF): A volume of water equal to one foot in depth covering an area of one acre equal to 43,560 cubic feet or 325,851 gallons.
Cubic Feet per Second (cfs): A rate of flow of water passing a given point, amounting to a volume of one cubic foot for each second of time. Equal to 7.48 gallons per second, 448.8 gallons per minute, or 1.984 acre-feet per day.
Water Demand Projections
The County and Town share an economic development philosophy which is to cultivate and nurture a vibrant community. This by definition requires continued growth of residents, businesses, second home owners and tourists.
A plan for any new water infrastructure is always based upon projections of future demand. In order to model the continued growth anticipated for a vibrant community, average historical growth rates for residents (1985-2008, using most recent State Demographer's Office data available) and for new Equivalent Units (1985-2008, using PAWSD historical data) were projected as continuing. Since 1986 the State Demographer's Office twenty year average growth rate was 4.2%, and the growth rate in EUs within the PAWSD service area was 5.6%. This historical time period includes economic highs and lows in the community.
For the next forty-six years (2009-2055),
the growth rate was more conservatively projected to allow for multi-year fluctuations in the economy and the current severe economic downturn. Averaging both historical data sets over five and ten year priods, the growth rate is projected to be 3.9% average per year.
Using a 3.9% average annual growth rate, the Equivalent Units in 2055 served by PAWSD will be 43,640, or approximately 29,000 residents (assuming current water usage patterns.)
What does this mean in terms of water demand and storage?
In addition
to population statistics, historical water use was also used in making
water demand projections. The historical average yearly water use prior
to the 2002 drought (1995-2001) was 331 gallons per EU (220 gallons per
person) per day, spiking to as high as 593 gallons per EU (395 gallons
per person) per day. The historical water use after the 2002 drought
(2002-2007) is 263 gallons per EU per day (175 gallons per person).
Although presented as a “per person” figure, this demand includes water
used by commercial businesses, tourists and fire protection as well as
raw (untreated) water use such as that used for irrigation by the golf
course.
Applying
the more conservative post-drought historical water demand to projected 3.9% growth, the total 2055 demand, on average, will be 13,610 acre-feet per year.
This 13,610 acre-feet represents the projected demand of PAWSD customers for raw and treated water, including the demand of those residents living outside the PAWSD boundaries who utilize the fill stations. It does not include the total demand of residents living outside the PAWSD service area but within the San Juan Water Conservancy District boundaries who also depend upon raw water. 13,610 acre-feet also does not include a one-year safety margin, which is defined as an extra year of annual water demand in staorage in case water is unavailable out of the rivers for a year due to a catastrophic event such as a drought, downstream user water rights call, landslide or contamination.
Using a future water demand of 13,610 acre feet, modeling for drought considtions similar to 2002, and allowing for a one-year safety supply margin, the Distict will require an additional 19,000 acre feet of storage in 2055. This is the minimum storage requirement. If growth slows from its historical twenty two year pattern, this amount will be adequate. If growth continues, on average, at the rate it has for the last 22 years, or if the community desires a larger reservoir for recreation purposes, 19,000 acre feet will not be adequate.
Studies
The studies to be conducted as part of this Dry Gulch project include:
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Projected costs of the reservoir to be constructed in one or two stages
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Evaluation of the capacity of the pumping plant on the San Juan River to fill Dry Gulch Reservoir
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Cultural and environmental studies, particularly in-stream river flow modeling and endangered species
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Other pre-construction technical studies, such as engineering, financial, legal and other services
Click here for studies that have been completed to date.
Design
In June 2008, the Board approved awarding a contract to MWH Americas, Inc. for the preliminary and final engineering of the new San Juan River diversion, pump station and pipeline and the Dry Gulch Reservoir dam.
Briliam Engineering is designing the new Dry Gulch Water Treatment Plant.
Davis Engineering Services is doing the survey work and will design the distribution system.
Steve Harris of Harris Water Engineering, Inc. is the Project Coordinator.
The Project Team of engineers and PAWSD staff held a project kick-off meeting on August 25, 2008, and continues to meet quarterly.
Land Acquisition
PAWSD, together with the San Juan Water Conservancy District, recently purchased 661 acres of property for the Dry Gulch Reservoir at a cost of approximately $9.8 million. This property is necessary no matter what size a reservoir is ultimately constructed (the maximum site capacity is 35,000 acre feet). A portion of the property will also be used for the new Dry Gulch treatment plant and pump station from the San Juan River.
Acquisition of approximately 140 acres of additional private land are currently under negotiations.
In 2007, the Conservancy District received a grant from State SB 179 funds of $1 million for the property purchase. The remaining costs of acquiring the private property shall be funded through a low-interest loan from the Colorado Water Conservation Board.
Simultaneously, PAWSD and the Conservancy District are pursuing a Forest Service Special Use permit and/or land exchange for the remainder of the property required. This land is also needed regardless of the reservoir size. Click here for Dry Gulch area map .
Permitting
It will take approximately 12 years to obtain all necessary permits for this project.
Permits that will be required for this project include:
• US Corps of Engineers 404 permit
• US Forest Service Special Use permit
• CDOT highway access permit
• Colorado Division of Water Resources approval of dam designs
• Colorado Division of Wildlife review of habitat evaluations
• US Fish and Wildlife Service Endangered Species Section 7 Consultation
The Forest Service Special Use permit application is currently in process.
Further questions? Click here!
