Dillon Dam Maintenance Update – January 6, 2015

Posted on January 6th, 2015

We spoke with Denver Water again late yesterday and have some additional insight into the completion of the ongoing maintenance project, as well as the process for getting the whole system back online to normal operations. Keep in mind that we are fish-heads, not engineers so, some of our verbiage may be a little generic and lacking in proper terminology. Hopefully we’ll get the information to you in a logical manner.

Due to inclement weather over the past month, the project is running further behind and now appears to be set for completion around the middle of the month, maybe the 15th, give or take a few days. However, when that does happen, it won’t be an immediate release from the bottom of the reservoir.

We mentioned in our last post here, that there would be a period where the release would be a mix of bottom flow through the outflow works along with water siphoned from near the surface. That will still happen but, we found out a little more about the process involved in that and it makes pinning down a specific date for seeing a full “tailwater” release a little tougher to call.

Once the work is done, Denver Water will need to back fill the outflow works with water; think of this as priming the pump. In order to assure a smooth transition of water into the empty drain from the lake, the drain will first be filled to minimize that impact. This process will take some time, potentially 1 to 3 days. Then the mix of top and bottom water can begin. Once that process assures the system is ready, another 1 to 3 days, then the tailwater can take over. So in reality, this whole switch could take up to a week to fully move to a Mysis-rich bottom release, which puts the date of impact closer to the 21st of January. And of course, that is if everything goes as planned, with no glitches.

After all of this happens and we get into a “tailwater” release, there is still a little uncertainty in how long the run will be and at what cubic feet per second. At minimum, Denver Water would like to purge about 6,000 acre feet of water and ideally release it at a flow near 250 cfs. However, due to it being winter and the river having a fairly sizable snow/ice load at the moment, it is unclear if that will cause any limitations. Those questions won’t be answered until the release starts.

Any flow over 100 cfs is a positive Mysis environment on the Blue River. Ideally we would like to see it between 200 and 300 cfs for as long as possible. This should give anglers the best conditions for winter/early spring fishing possible. As well as, provide plenty of food for resident fish that have been lacking the added boost of the shrimp since August.

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