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HomeMy WebLinkAboutMemo - Mail Packet - 2/14/2013 (8)Utilities C'}" electric storrnwater wastewater water Of Fort Fort Wood PO Box 560 Collins Collins,Fort CCO CO 80522 970.221.6700 970.221.6619 -fax 970.224.6003 - TDD utilities®Icgov.com lcgov.cowti lities MEMORANDUM DATE: February 11, 2013 TO: Mayor and City Councilmembers THRU: Darin Atteberry, City Manager_ Brian Janonis, P.E., Utilities Executive Director FROM: Kevin Gertig, Water Resources and Treatment Ooerations Manager Adam Jokerst, P.E., Water Resources Engineer/v RE: February 5, 2013 City Council Meeting — Agenda Item #28 — 2013 Water Supply Management Action Plan During discussion of water restrictions at the February 5, 2013 City Council meeting, a Councilmember asked: What impact would a water storage project like Halligan Reservoir have on water restrictions both in light of the High Park Fire and without the fire given the current drought situation? Below is a short response to this question, followed by more a detailed explanation. In short, Halligan Reservoir will reduce the frequency and severity of water restrictions during droughts. Even with the impacts of the High Park Fire, having operational storage capacity such as Halligan Reservoir this year would have reduced the level of or eliminated the need for currently planned restrictions. Current Scenario with Fire Impacts The Hewlett and High Park Fires burned roughly 10% of the Poudre River watershed. Although this is a relatively small portion, the fires have led to a large amount of ash, sediment and debris depositing in the Poudre River. During periods of rain or fluctuating water levels, this sediment becomes suspended resulting in water quality degradations that may preclude diversions for treated water supplies. Because the City typically diverts approximately 50% of its annual treated water demands from the Poudre River, the fires have the potential to impact a significant portion of the City's water supply. Coupled with the ongoing drought conditions and current low snowpack, there is a large degree of uncertainty in planning this year's water supply. Halligan Reservoir is located on the North Fork of the Poudre River, and its watershed was not significantly impacted by fires. However, the City's diversion points off the Poudre River are Fort Collins upstream of the North Fork on the mainstem, which was affected by the fires. Given this situation, it has been questioned whether or not Halligan Reservoir could have benefitted the City this year given the present fire situation. To answer this question, Utilities staff considered two operations that would have allowed the City to make use of water stored in Halligan Reservoir, were it available, in the coming year. First, releases from Halligan Reservoir could be used to augment diversions of Poudre River flows during periods of sufficient water quality. The City is currently diverting Poudre River water during winter months when stable and low -Flow conditions yield sufficient water quality. Releases from Halligan Reservoir could supplement river diversions when such diversions are allowed. Second, through cooperative agreements with irrigation companies in the Poudre basin or through arrangements with other entities (for example, a temporary carriage contract through the U.S. Bureau of Reclamation), it is expected that the City would be able to exchange a large amount of water stored in Halligan Reservoir for Colorado -Big Thompson (CBT) water stored in Horsetooth Reservoir. CBT supplies in Horsetooth Reservoir were not impacted by fires to the same degree as Poudre River supplies, and thus are readily available for treatment. Through these potential exchanges, Halligan Reservoir would provide an effective means to obtain additional CBT water during periods when Poudre River supplies are unavailable. The above Halligan Reservoir operations would yield additional firm water supplies to the City, which would reduce the projected deficit between supplies and demands in the coming year (and subsequent years), and would reduce or eliminate the need for planned water restrictions. Utilities staff estimates these Halligan Reservoir operations could yield up to 6,000 acre-feet or more of additional firm supplies, an increase in supply of 30% to 40% in the coming year. However, without knowing exactly how the fire will impact Poudre River supplies or what CBT quota will be allotted to the City, it is impossible to state with certainty the level of water restrictions that would be recommended this year were Halligan Reservoir constructed. The figure on the following page illustrates the benefits of having Halligan Reservoir on the City's water supplies and restriction levels. Future Drought Scenarios As with the current drought situation, Halligan Reservoir will provide the City operational storage to meet treated water demands during future drought periods. It is sized to meet to City's water demands during a 1-in-50 year drought scenario while providing a storage reserve factor as directed in the City's Water Supply and Demand Management Policy approved by City Council in November 2012 (Resolution 2012-099). When constructed, Halligan Reservoir will allow the City to meet demands without implementing water restrictions during future droughts up to the 1-in-50 year design. Without the reservoir, restrictions would be required for the City to meet anticipated future demands during droughts less severe than the I-in-50 year drought. Water restrictions will still be required in the future for droughts more severe than the I-in-50 year criterion and may be needed during water supply disruptions such as fires and system outages; however, Halligan Reservoir will likely reduce the severity of restrictions during such periods. The following figure shows water restrictions required with and without Halligan Reservoir both in the current fire -impacted situation and in the future during a 1-in-50 year design drought. Values provided in the figure are preliminary approximations for illustrative purposes only. 2 F, itty of Figure 1: Supplies, demands, and restrictions with and without Halligan Reservoir. y 50 000 d. Current Conditions, Future 1-in-50 Year With Fire Drought, No Fire a O C nl y Fmn Supply ■ O Guncertain Supply �01y ev �r n 25 000 Increased supply hom Rallipn C Unrestricted ZDemand Restrictions rarawceda'r iy ry 0 Supply Demand Supply Demand Supply Demand Supply Demand Without Halligan With Halligan Without Halligan With Halligan In the current fire -impacted condition, two types of water supplies are shown: firm supplies and uncertain supplies. Firm supplies are water sources that are reasonably sure to be available for treatment. Uncertain supplies are water sources whose availability this coming year is presently unknown. Such supplies remain uncertain because the final COT quota has not yet been set and it is yet unknown how the fires will impact the Poudre River this summer. The amount of uncertain supply is identical for conditions with and without Halligan Reservoir. Fires are not considered in the future 1-in-50 drought condition; therefore, only firm supplies are shown. Whenever demands are greater than available supplies, restrictions are required to reduce demands. Hence, restrictions are shown anytime demands exceed the firm supplies. Given that a large segment of supplies In the coming year is uncertain (i.e. not firm), so too are the level of restrictions shown. If additional supplies become available, the severity of restrictions would decrease. Storage capacity such as Halligan Reservoir increases firm supply, which reduces the range of potential restrictions. Halligan Reservoir may not completely eliminate the supply and demand deficit, but were the City to have such storage capacity in the coming year, it would rely less on uncertain supplies. Halligan Reservoir is sized to meet all demands in future 1-in-SO droughts; consequently, higher levels of restrictions are certain without Halligan Reservoir (or additional firm supplies), but are not required with Halligan.