Wednesday, January 31, 2018

Matilija Dam - water quality

Matilija Dam,  decaying debris, Jan 26, 2018 

Ventura River preserve, Jan 30, 2018
Two weeks after the flood, floating debris remains trapped near the dam.  There was a significant input of organic matter that has stagnated in the reservoir, as evidenced by the smell.  Flows entering the reservoir from upstream in Matilija creek as well as in the North Fork Matilija Creek are much cleaner.   This is having a tremendous impact on downstream water quality all the way to the ocean.

This is consistent with known reservoir impacts in general, and our experience monitoring Matilija Dam over the years.  Under normal circumstances Matilija reservoir often retains suspended particles for weeks following a storm, greatly extending the negative effects of turbidity downstream.  In the current situation, whatever has accumulated behind the dam has magnified this problem.

Matilija dam and reservoir, Google satellite image, after fire and flood, Jan 13, 2018

Rodents seemed most susceptible to wildfire
It is likely that any wildlife killed by the fire along with materials from destroyed residences has washed into the reservoir along with the vegetation that was stripped from the floodplain.  Extremely high turbidity killed fish in the reservoir.  The recent warm weather and stagnant water has created a toxic brew, which is slowly being released downstream.

Although there have been concerns raised over the years regarding the negative effects of releasing reservoir sediment, this illustrates how removal of the dam will in fact enhance water quality once the initial flush is complete.

Deer carcass, found elsewhere in the
watershed following Thomas Fire

Dead bass, found downstream in the Ventura River Preserve

Upstream of dam, Jan 26, 2018
Downstream of the dam, gauging station, Jan 26, 2018

Ventura River Preserve  Feb 12, 2018

On February 3, 2018, Santa Barbara Channelkeeper's Stream Team volunteers collected water samples throughout the watershed.  In particular, the results demonstrated a significant impact from the dam, with bacteria and nutrient levels spiking below the dam and slowly decreasing downstream. Note that these levels were orders of magnitude above those that have been recorded since 2001!

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