Water Committee Agenda and Packet 2013 01 31

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Jan 2013 Draft Revisions WW ATER AND EATHER In Colorado, weather plays a significant role in determining the amount of water available. It is relatively easyto project water needed for a given development or recreational facility. It is much more difficult to integrate the effect of variations in weather on the total amount of water available to Louisville. Approximately half the water used in Louisville isfor landscape irrigation. The other half is used for domestic, industrial, and commercial purposes. HRSWSB? OW ELIABLE HOULD A ATER UPPLY E When the City adopted the current Raw Water Master Plan, Council selected a drought event of 24 months with a 50-year reoccurrence interval as the drought event that the water system should be designed to withstand. The 2002 drought eventwasmore severe than theanticipateddesign drought. In fact, the 2002 drought was considered, until recently,to be a 1 in a 300-year drought event within the local water supply basin. This means the 2002event waswell outside any Deleted: events of reliability criteria established for Louisville’s water supply system. In spite of this,the City was Deleted: were able to supplysufficient water quantity to satisfyessential health and safetyneeds,as well as Deleted: water and still maintain landscape materials in the community. Information from the National Oceanic and Atmospheric Administration (NOAA) suggests that climate change associated with global warming may result in more frequent and prolonged drought events. DRP ROUGHT ESPONSE LAN WhenLouisville is facing a drought event, the City should be prepared to implement an appropriate predefined drought response plan. However, determining when a drought has begun can only be done in hindsight and determining when a drought will end is only possible if one can predict the future. Using historical information regarding drought events, stream run-off, and related factors is the only way to prepareappropriate projections to be incorporated into an overall drought response plan. DI ROUGHT NDICATORS It should be kept in mind that a drought will likely begin with a small event and become more severe. Droughts may last a month or several years. Withthis plan, the City should be able to Deleted: move through escalate the drought severity ratings as a drought continues. When projecting water supply for Louisville, one typically looks at the critical period of March, April and May. Historically this is the time when the reservoirs approach their lowest level while at the same time snow pack measurements provide reasonable projections for runoff for the coming season. The amount of water in storage and the projected amount of available runoff determines the City’s ability to meet water demands. At best, drought indicators are only a guideline. It takes detailed analysis and extensive experience to understand within a given set of circumstances the amount of water likely to be available to the community. In many cases, the same amount of snow pack can have significantly different runoff patterns resulting in large variations in the amount of useable water. 2