Matt Horne’s informative letter about steelhead trout should not otherwise be taken as a warning about sediments trapped behind the Rindge Dam. (The Malibu Times Opinions, November 4, 2004). Despite the Corps of Engineers’ “$2 million” study regarding the dam’s removal, it is not a matter of concern that the dam “… impounds 600,000 cubic yards of saturated sediments perched a short distance upstream from Malibu Colony.” Horne’s image of a sort of Damoclean deluge threatening the Colony as well as other areas of the Malibu Creek floodplain is without merit.
The dam is 1.9 miles upstream from the nearest habitation, and that reach of Malibu Creek, which contains much sediment, has a gradient of about 0.02. For the unenlightened, this is geology talk for saying that there is no way in hell the impounded sediments could threaten developments in the floodplain. They are not sitting up there on ball bearings just waiting for the dam to be removed. Streams don’t work that way. They simply carry as much load as they can, depending upon the flow volume and velocity. The present streambed load through the flood plain is a function of flow over the dam, the sediments downstream, and the gradient. Removing the dam won’t change that regimen except that a certain amount of “mining” of finer-grained fractions downstream would be reduced. So far, in the eighty-some years of the dam’s existence, this has not been significant; otherwise, the sand bar at the beach would have disappeared.
If the dam must be removed, the way to do it is to drill through its base to eliminate saturated conditions and then incrementally notch it. In this way, the stream will remove the sediments, the stream load will remain the same in the floodplain, and the Corps can quit screwing around so that the $2 million can be applied to some useful endeavor.