Winter Lake Level Q&A

flood
Dave,
Just a quick question, during the recent storm the lake level was a bit higher than summer levels for a short time. My question is was the new weir fully open? In your opinion had the lake been at summer levels ( like some home owners would like to see) would there had been a larger issue with flood control?

Thank-you,
Gary Stonewall

The direct and short answer to your question is YES there would have been a greater impact to lake front properties and the weir was open all the way.

The summer lake elevation is maintained around 12.2 feet. The normal winter lake elevation is maintained between the ranges of 9.0 to 10.5 feet, because of the amount of flow (400-600 cfs) the lake receives from Fairview Creek during large rain events or back to back storm events like we had during the last storm event. The lake elevation will raise anywhere between two to three feet depending on the event size and duration. If the lake would have been at 12.2 feet during this last storm event the lake elevation would have gone up to 14.5 to 15.0 feet. This is not acceptable for two reasons; 1) a few of the houses on the northeastern corner of the lake at impacted when the lake elevation reaches 14.0 feet, 2) the district is mandated by FEMA to maintain an internal water elevation at or below elevation 14.0 feet. Because the lake elevation was at 10.1 feet at the time of the storm the lake rose to elevation 13.5 feet and all were protected.

It is my opinion, even if the houses on the northeastern end of the lake construct some form of barrier to protect their properties from a lake elevation of 14.0 feet, the lake elevation should always be drawn down during the winter for added protection to the lake front properties.

Why, if the lake was maintained at elevation 12.2 feet during the winter months the district could change its pumping requirements to maintain a water elevation in the lake between 13.5 to 14.0 feet elevation during these large rain events, however if the pump station lost power and we can’t pump for several hours the lake would not have any storage and the lake elevation will increase very rapidly, depending on the incoming flows, what stage of the event is in and if we have back to back storms coming in. We are dealing with Mother Nature and I feel we should always plan for the worst case scenario and a calculated margin of safety.

Hope this helps, if you want to talk in more detail let Bob or I know and we would be glad to meet with you and or your Board.

Dave Hendricks, Deputy Director
Multnomah County Drainage District # 1
1880 NE Elrod Dr.
Portland Oregon, 97211
(503) 281-5675 x 302
(503) 281-0392 Fax
(503) 936-1366 Cell
dhendricks@mcdd.org
www.mcdd.org

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