Taking advantage of this rainy winter at the Elwha

What a soggy winter in the northwest! The maps below were generated from the National Weather Service’s AHPS (Advanced Hydrologic Prediction Service). The first shows shows national rainfall totals for the past 60 days. More than 30-50” of rain have fallen in the the Olympics, which is above normal (see second map).

December 13, 2015 60-Day Observed Precipitation

December 13, 2015 60-Day Departure Precipitation

What does this mean for the Elwha River? Some pretty big flow events. Below is a graph generated from the USGS NWIS (National Water Information System) for station 12045500 at McDonald Bridge, 8.6 miles upriver of the coast. This shows the river hydrograph, or water discharge record, since Sept 14, 2011, the approximate start date of dam deconstruction. This winter’s events are the biggest since 2011 – note that the left axis is a log scale, making this year’s flows even more impressive. 

graph

When rainstorms bring these increases in river discharge, more sediment is exported from the former reservoirs. In response to this winter’s active storm season, we teamed up with Ian Miller at WA Sea Grant (see his Coast Nerd Gazette) and Dave Thoreson from UW Oceanography Tech Services to deploy a small instrument package offshore of the river mouth. We caught a break between storms on Dec 4, 2015 and launched the “mini tripod” in Freshwater Bay, complete with upward- and downward-looking acoustic doppler current profilers (ADCPs), a temperature/salinity/turbidity/wave sensor, an optical backscatter sensor (OBS), a light sensor, a “sedimeter” (32 OBSs on a stick), and a couple of sediment tube traps. Here’s a photo of the system ready for deployment from the R/V Wealander, with Dave at the helm and Ian helping the launch:

WealanderLaunchElwha4Dec2015

We also collected water-column profiles using a conductivity/temperature/depth (CTD) sensor with optical backscatter sensor (OBS), as well as a laser particle sizer (a LISST). With these measurements, we can look at the structure of the muddy, freshwater “plume” created by the river water flowing on top of the more saline ocean water. By analyzing the structure of this muddy, freshwater lens, we can better understand where the mud is going when it floats out to sea. Below, Ian prepares to deploy the LISST while Dave drives and Andrea collects water samples. The Wealander was a great platform for our rapid sampling!

IanMillerLISSTElwha

DaveAndrea4Dec2015

The instrument package will remain on the seabed and collect data every hour until we retrieve it in February…fingers crossed for another good weather window!