Probable Maximum Precipitation Needs Assessment for Montana Issues
Probable Maximum Precipitation Needs Assessment for Montana
Issues • Probable Maximum Precipitation (PMP) is used nationwide by States and Federal Agencies to design spillways • Since 1940, the National Weather Service has been providing guidance for determining PMP’s • Most PMP documents require updating (last updated 1963 to 1994) • Funding to the National Weather Service to update PMP documents has ceased. • National “Extreme Storm Events Work Group” looking into problems with outdated PMP documents (last meeting May 2014 – where is this going? )
Recent Actions • States have taken the initiative to develop regional updated PMP estimation methodology Ohio Texas (underway) Nebraska Virginia (underway) Arizona Wyoming Colorado (underway) New Mexico (underway) • Regional PMP studies are expensive! • Wyoming - $800, 000 • Colorado - $1, 000 • The benefits to Montana of a regional PMP study is unclear • The financial feasibility of a regional Montana PMP study is unclear • Montana has been advised to complete a “Needs Assessment” to determine if completing a Montana regional PMP study has merit and is feasible.
State of Montana Spillway Standard – based on potential for downstream loss of life PMP Loss of Life 1000 5 5000 Recurrence Interval
State of Montana Spillway Standard PMP Loss of Life 1000 Most Montana Dams 5 5000 Recurrence Interval
State of Montana Spillway Standard PMP Loss of Life 1000 • Federal Dams • FERC regulated dams • Tailings Dams • State regulated dams with large population at risk 5 5000 Recurrence Interval
State of Montana Spillway Standard State regulated dams with moderate population at risk PMP Loss of Life 1000 5 5000 Recurrence Interval
Needs Assessment Components 1. Evaluate benefits of regional PMP for Montana • # impacted dams – is it great enough to warrant expenditure 2. Value of having updated PMP methodology • Other States report updated PMP’s are “better science, but not necessarily lower values” Ø Makes it a difficult sell to dam owners 3. Obtain perspective of other Montana Dam Owners • Federal Montana dam owner perspective on issue is unknown • FERC regulated Montana dam owner perspective on issue is unknown 4. Tailings Dams – New legislation requiring PMF for all dams (sponsored by Montana Mining Association) • Mining association perspective on issue is unknown 5. Evaluate problems with existing PMP methodology 6. Financial Feasibility of completing regional PMP study • Legislative funding highly unlikely (i. e. 0% chance) • Investigate other funding options • Mining association contribution?
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