Friday, April 13, 2018

March Rains - fires, flood, drought, and sand

Matilija Dam, March 22, 2018

They aren't calling it a "March miracle," but to many of us it felt like it.  A fairly steady wet period delivered around 8" of rain to the Ojai Valley, and rescued this year from the record books.  Seasonal totals range from 6" in Ventura, to over 11" in Ojai, with Matilija Canyon receiving over 16". This is just a bit less than half the "average" rainfall for our watershed. 

Water supply, April 1 2018   (from Ventura River Water District) 


The Ventura River Water District monitors levels in the Upper Ventura River Groundwater basin as well as Lake Casitas.   Note that the groundwater (blue line) responds quickly to rainfall compared to the large volume of the reservoir.  This graph shows the general downward trend in water storage, which unfortunately was not helped much with this season's rainfall.  

Water managers are also concerned that the Thomas Fire is impacting supply.  Huge volumes of ash and silt eroded from the burned landscape and deposited within the riverbed, possibly hindering infiltration into the underground aquifer.    So far this year the blue line shows a  relatively small uptick compared with past seasons.   

The March rains did mobilize a bit more ash, but more noticeably the river has again remained turbid (brown) for an extended period due to high levels of silt eroding from the bare mountainsides.

Flows remain high and silty in the Ventura River Preserve, March 30, 2018



This hydrograph for the month of March (thru April 13) shows flows at Foster Park (green line...8500) and below Matilija Dam (red line...4495).  The graph clearly shows storm peaks throughout the month, with the final storm registering around 4000 cfs.   This plot also confirms observations that river flows have remained relatively high following the final storm.  This may indicate significant changes in the hydrology of the watershed due to the Thomas Fire.  On the other hand, USGS data show that flows are now comparable with the historic median. The Upper Ventura River Groundwater Sustainability Agency (UVRGSA) recently commissioned studies to monitor and assess the situation.  

Flows at Foster Park, Spring 2018



Ventura Rivermouth, March 28, 2018

Finally, this aerial view of the rivermouth also shows silty water flowing into the ocean at Surfers' Point.   Not surprisingly,  Surfrider Ventura's new Blue Water Task Force and County testing found poor ocean water quality following the rains.  But look at that sand!

The gun turrets are now buried with sand, showing how the delta has grown compared with Ventura river mouth after the 2017 flood.  With fire and flood, a flowing river and eroding hillsides make for wider beaches...