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Hydrology of the Beaver Creek Estuary at Ona Beach State Park, Oregon

Contact: Adam Stonewall

Background

Beaver Creek near its mouth

Beaver Creek near its mouth at low tide (Photograph by Karl Lee, USGS)

The Beaver Creek estuary, at the terminus of a 34 square mile basin just south of Newport, in Lincoln County, is home to diverse native flora and fauna. It is part of Ona Beach State Park, which is administered by the Oregon Parks and Recreation Department (OPRD). The estuary extends about 3 miles upstream from the mouth. The Beaver Creek basin lies between the Yaquina River basin to the north and the Alsea River basin to the south.

OPRD has recently acquired property in the estuary, and is developing plans for restoration to a more natural condition. Federal lands in the North Fork of Beaver Creek basin (upstream of the estuary area) are designated as a Key Watershed in the Northwest Forest Plan, making it a high priority for maintenance and restoration of aquatic and terrestrial habitats and species. Lower reaches of the Beaver Creek watershed are designated as critical habitat for coho salmon. Restoration will require an understanding of the tidal and storm-surge dynamics of the Beaver Creek estuary, as well as of the salinity component of stream water and thermal regime of the estuary.

Study Objectives

The USGS has a cooperative agreement with the OPRD to collect and analyze the data from 2010-2013 to necessary to develop wetland restoration strategies for the Beaver Creek estuary and to evaluate the results of restoration efforts. The goals of this 4-year study are to:

  • Assess the extent of tidal influence in terms of tidal stage and salinity.
  • Determine the dominant sources of water to the estuary.
  • Collect baseline hydrologic data to assist in evaluating restoration efforts.

Approach

Measuring specific conductance and temperature

Measuring specific conductance and temperature (Photograph by Karl Lee, USGS)

This study measures the extent of tidal and storm-surge influence, as well as gradients of specific conductance and temperature. Two sites are instrumented with continuous water level, temperature, and specific conductance recorders. These sites are located on Beaver Creek at the Highway 101 bridge (Beaver Creek at Highway 101 near Seal Rock, Oregon, USGS site number 14306085), and just downstream of the confluence with South Beaver Creek (Beaver Creek below South Beaver Creek near Seal Rock, Oregon, USGS site number 14306080). A third site on Beaver Creek, located upstream of the State Park boundary, (Beaver Creek at NW Beaver Valley Drive, near Seal Rock, Oregon (USGS site number 14306065) monitors temperature only. In addition, about three times each year, streamflow and water-level measurements are made at the sites on Beaver Creek as well as near the mouth of South Beaver Creek (USGS site number 14306075). Direct instream specific conductance measurements were made on July 14 and November 12–13, 2012.

Measuring streamflow

Measuring streamflow (Photograph by Karl Lee, USGS)

The pattern of water-level fluctuation, coupled with the specific conductance and temperature data, provides an indication of the predominant source of water to the estuary. Periodic streamflow measurements identify flow contributions to the estuary from upland sources. These measurements are made at sites upstream of tidal influence during periods of relatively stable streamflow. The sites are visited bimonthly. Each field visit consists of verifying operation of the sensors with a portable, calibrated test unit, collecting the stored data, and, when appropriate, making streamflow measurements.

 

Summary

USGS data from 2010–2012 has provided insight into the dynamics of the Beaver Creek estuary’s hydrology and water quality:

 

  1. Water temperature can be an indicator of estuary hydrology and thermal regimes in the study area. Oregon State water temperature standards stipulate that a 7-day moving average of the daily maximum temperature shall not exceed 18 degrees Celsius (°C), equivalent to about 64 degrees Fahrenheit. The 7-day moving average of maximum water temperature exceeded 18.0°C during 2010–12 at these gages:
    • Hwy 101 gage, 25% of days
    • South Beaver Creek, 20% of days
    • NW Beaver Valley Drive, no exceedence
  2. These exceedences of the standards could have implications for basin restoration plans.

  3. High specific conductance (above 20,000uS/cm) in water at the Beaver Creek at Hwy 101 site results from storm surges, when seawater overtops a sand bar riffle near the mouth. Overtopping events correlate with tides above 9.5 feet, measured at the NOAA tidal stage gage at nearby Yaquina Harbor. Specific conductance data from the most downstream Beaver Creek site, Highway 101, indicate that storm-surge conditions caused seawater to enter the estuary 13 times during September–May in 2010–2012.
  4. Periodic discrete flow measurements over a range of seasons and flows at the stream sites can help understand the upland flow contribution from Beaver Creek tributaries and, at times, possible seawater inflow. Flood discharges were determined during storm flows in January 2011 and 2012 and during low flows of September–October 2010–2011.
  5. A record of 2011–2012 detailed stream cross sections of water temperature and specific conductance at the three sites has provided valuable information about water temperature and specific conductance stratification during storm-surge periods. These variations through the water column are indicators of tidal dynamics and brackish water residence time. For example, in October 2011, specific conductance varied in the water column top to bottom by as much as 45,000 uS/cm at both the Highway 101 and below South Beaver Creek sites. Water temperature for the same period varied in the water column by as much as 4.9°C. These data will help park managers assess floral and faunal possibilities for future Beaver Creek ecosystem restoration efforts.

Future Studies

Additional analysis of 2010–2013 baseline flow, temperature, and specific conductance data will be needed to evaluate the results of ongoing restoration efforts.

 

Poster: Hydrology of the Beaver Creek Estuary PDF (1.2 MB)

Data From Monitoring Sites

Data from direct measurements made July 14 and November 12–13, 2012. (SC = specific conductance.)

Water Quality in the Mid-Coast Basin (from Lincoln Soil and Water Conservation District)

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