Ventura River Ecosystem: Matilija Reservoir March 2020

Wednesday, March 25, 2020

Matilija Reservoir March 2020

Matilija Reservoir March 17, 2020

It appears that our March rainfall event moved more sediment into Matilija reservoir. Flows in the upstream delta are currently split so that the remnant reservoir has two inlets, one on each bank. Last year saw significant deposits at the right bank (background of this photo.) Here, new deposits are visible on the left bank (in the foreground of the photo).

Matilija Reservoir March 21, 2020

By March 21, the reservoir elevation had been lowered due to Casitas Municipal Water District's operations to release water from Matilija reservoir for downstream diversion at Robles. This revealed the extent of the sedimentation, and allowed the inlet flows to erode a channel. Note that although the creek was flowing clear, the reservoir still had suspended sediment lingering from earlier in the week.

The hydrograph below shows the flows recorded at USGS gages just below Matilija Dam (red line 11114495) and downstream at Foster Park (green line 11118500). The difference between these lines is approximately what is diverted into Lake Casitas (excepting other inflow from North Fork Matilija Creek.)

Note the small peak at Foster Park on March 19 when the operation of Robles diversion was temporarily interrupted for maintenance, perhaps due to the influx of sand and gravel moving downstream.