May 6,2023 Explanation of Dam Management by Malcolm Ray

This morning at about 10:15 AM I shut all the gates of the dam. The lake elevation at the dam is still about an inch high but it will come down to the target elevation of 402.5 MSL soon.

Prior to Sunday most of the weather predictions were for about 3” of rain. We were just finishing the sewer district drawdown so the dam had been partially open. Sunday morning we were about 12” below the flashboards (about 401.5 MSL àMSL = mean sea level elevation) so with 3” of rain I was expecting the water level to rise to about 403 MSL (6” over the flashboards). That would be high but not unusual. We got quite a bit more than the predicted 3” so when Dave Bowen and I checked the dam Monday morning at 7 AM we were at 403.2 and rising. Deciding what to do is a balance of three things: minimize lake flooding, minimize downstream flooding, and ensuring the level does not exceed 404 MSL. At 404 MSL the flashboards are designed to fail in order to protect the dam structure. If that happened a lot of water would flood into downtown and we would have a repair job to do before we could get back to normal operation. Releasing enough water to stay below 404 MSL is, therefore, the first priority. We raised the middle gate 36” at 7:00 AM on Monday and then raised the west gate 48” around mid-morning. At 5 PM Monday the level was 403.8 MSL. We did not want to open the east gate since 140 by the potato farm, Bixby Road, and Cross Street were already under water. We felt like we were at the crest so we left the west and middle gates opened and the east gate closed. We checked a few more times in the evening and the level had stopped rising so our guess was correct. By Tuesday morning the level was down to 403.6 MSL and slowly falling so I closed the west gate off at about 5 PM. At 2 AM on Wednesday the level was down to 403 MSL and holding. The last few days it has been slowly but steadily falling such that this morning it was 402.6 MSL.

Dave and I have been managing the dam since it was constructed over ten years ago. In that time we have only had one other occasion where we had 3” (3 Jun 2012) or more of rain and that time too we kept the level just below 404 MSL to protect the flashboards.