[Posted by Chuck Almdale]

Steelhead Trout. Source: KCRW – Malibu Creek Steelhead

This 9-minute audio was broadcast on KCRW’s Greater LA report today, 17 May 2023.
This link takes you to both the audio recording and KCRW’s text.

Featured on the audio is local fish expert Rosi Dagit, who in 1998 discovered Steelhead Trout in Topanga Creek, much to everyone’s utter disbelief. Then in 2017, below Rindge Dam in Malibu Creek, she discovered a female Steelhead trying to head upstream to spawn. To her great sadness the Steelhead expired despite her attempts to save it.

Beginning over 30 years ago and continuing for 10-15 years, I attended an seemingly-unending series of discussions concerning Malibu Creek and Lagoon, under the auspices of the unwieldy-named Malibu Creek Watershed Advisory Council and Steering Committee. It was fun, frustrating and enlightening.

One of the reports it produced was the 1995 Malibu Creek Watershed Natural Resources Plan which came up with 44 action items over which I sweated blood for a few weeks. Out of all this work and conferring came the 2012 Lagoon Restoration (I call it reconfiguration), which people including me still praise and blame. Many problems we discussed then still exist.

Link to watershed maps.

Rindge Dam, aerial photo, 3 miles upstream of Malibu Lagoon.
ScreenSnip Source: CalTrout – Rindge Dam

Among them is the problem of Rindge Dam, located about 3 miles up Malibu Creek. The short summation of problems: 100 years old and 100 ft. high, impassible by fish, now filled to the brim with estimated 780,000 cubic yards of sediment, residents downstream worry about a flood of sediment should the dam come down quickly, the sediment provides lateral support for canyon walls, dam removal might cause canyon walls and Malibu Canyon Road to collapse.

This Rindge Dam film from California Trout mentions how “restored sediment transport supports a healthy beach and prevents erosion,” an opinion with which I and I’m sure all surfers will agree. But if that is true, perhaps at least some of the 780,000 cubic yards of sediment behind the dam should be removed by letting it flow downstream through a paced reduction of dam height, allowing the creek to erode the silt and carry it away naturally and gradually. The current plan calls for hauling all the sediment away in trucks.

I have a suggestion.

If it’s going to take ten years to accomplish this removal, as the film suggests, perhaps instead of waiting 8-9 years before beginning the project and doing all the work in 1-2 years, they could cut a V-shaped notch 1-5 feet deep in the top of the dam now and allow the creek to carry the silt away gradually. When sufficient sediment has flowed away, cut the notch a foot or two deeper and wider. Over 10 years you could do this every three months or 40 times total, cutting the notch 2.5 feet deeper (on average) each time. After 10 years, the silt is gone. It has flowed down to the beach and offshore sand reefs where it now “supports a healthy beach and prevents erosion” and you can pull the remaining concrete dam down as it’s no longer impeding or supporting anything. If the sediment doesn’t flow away quickly enough, then use trucks.

We could have started this 20-30 years ago, and the whole project might now be 10 years in the rear-view mirror.

Just a suggestion.

A typical dump truck like the one above holds 10-14 cubic yards (270-378 cu.ft.). A typical cubic yard of dirt weighs 2200 lbs. and of gravel 3000 lbs. 780,000 cubic yards equals: 858,000-1,170,000 tons of sediment, or 2,060-2,890 truckloads (like the truck above) to haul away.
Source: Lynch Truck Center

There are reasons why this problem and discussion has continued for decades.