GrokSurf's San Diego

Regular visitors to San Diego’s Lake Murray Reservoir are probably accustomed to seeing the water level rise and fall somewhat. Indeed, the city changes the elevations on all its reservoirs frequently depending on the demands on the system or other circumstances.

One of those “other circumstances” made itself visible recently when the water level dropped much lower than usual, but warm weather and high demand were not the reason, nor was it because of the trunk sewer project underway nearby. This drawdown was actually related to the big rainstorm we had last January.

During those rains, the old corroded 48″ storm drain pipes beneath the lake’s service road at the northern end of San Carlos Bay clogged up and heavy runoff washed over the outlet, damaging the road (click photos for enlargements).

When the pipes clogged up, the road became a dam that quickly overflowed

Overflow washed out part of the road

Roadcut on opposite side revealed corroded pipes

At that time, a water department construction foreman told me the city might replace the old 48″ pipes with larger 60″ pipes but later the decision was made to install a concrete box culvert under the road.

The project needed to be done in two phases. The first phase was to install the box culvert and repair the road. That part is now done.

The new culvert measures 5' x 8'

The second phase involves work on the concrete-lined drainage channel toward the lake. That stage was put on hold, however, because it takes place in an area that is part of the Multiple Species Conservation Program. The program did not allow construction to take place until after Sept. 15, which is considered the end of bird nesting season.

With the deadline passed, work resumed and the reservoir water level was lowered to an elevation of about 83 feet to allow compaction of the soil that will be under the new concrete. Normally the lake elevation is around 93 feet with a reservoir capacity of 4,684.2 acre feet. The boat launch is affected as well since it can’t be used when the level is below 85 feet (boat rentals are no longer offered anyway but small private craft may be launched when levels are normal).

The view from Lake Shore Drive

Looking toward San Carlos Bay. At the usual lake level, I would be standing in water to take this picture.

Before concrete could be poured for the new channel, however, another delay became necessary. This time it’s because the San Diego County Water Authority has scheduled a shutdown of the untreated water supply in order to work on a valve at its Rancho Peñasquitos Hydro Facility. As a result, the city had to postpone the repair project and refill the reservoir in order to have water on hand during the shutdown. They’re refilling the reservoir now.

Water is added via the fill chute near Alvarado Water Treatment Plant (looks like a stream near center of photo)

The plan now is to resume construction near the end of October, so as the month progresses we’ll see the water level drop significantly again. The project which is fully funded by the Public Utilities Department budget (no tax dollars) is expected to be completed by mid- to late- November.

Rising lake bringing water back into the unfinished channel

[Update Oct 1, 2010]: The day after I took the above picture the supervisor in charge decided the water level was still low enough to finish the concrete work on the drainage channel, here it is. They’re now digging footings for a chain-link fence that will line the side of the road near the channel.

[Thanks to: Arian Collins (Supervising Public Information Officer, City of San Diego Public Utilities Department, Water Operations Branch) and John Liarakos (Media Relations Representative, San Diego County Water Authority) for their assistance with my questions]