Arroyo Colorado Water Quality Monitoring

Science Center Objects

As a result of being able to continuously monitor the water column in multiple depths, dynamic changes in water chemistry (such as those that result from barge traffic and large storms) now can be identified, thereby helping water resource managers better understand changes in water quality in the Arroyo Colorado.

Arroyo Colorado Basin

Arroyo Colorado Basin, Texas (from USGS Data Series 255)

The Arroyo Colorado flows 90 miles from near Mission, Texas to the Lower Laguna Madre, a hyper-saline lagoon that drains into the Gulf of Mexico. The river is used as a floodway as well as for the conveyance of commercial barge traffic. The river consists of a freshwater segment with inflow primarily provided by municipal wastewater effluent, and a tidally-influenced marine segment. The tidal segment has been designated as an impaired water body because of high bacteria levels and depressed dissolved oxygen values.

At U.S. Geological Survey (USGS) station 08470500 Arroyo Colorado at FM 106 at Rio Hondo, Tex., in the tidally-influenced segment, the water is typically saline, with specific conductance values ranging from approximately 1,000 microsiemens per centimeter at 25 degrees Celsius (µS/cm) near the surface to 50,000 µS/cm at 3 meters below the surface near the bottom of the channel. Dissolved oxygen concentrations at this site typically range from approximately 10 milligrams per liter (mg/L) near the surface to near 0 mg/L near the bottom. The water quality is often striated by depth, but mixing can occur from large storms or barge traffic.

Barge traffic on Arroyo Colorado

Barge traffic at the location often causes mixing of the typically highly-stratified stream.

In the past, multi-depth monitoring using separate monitors at different depths in the tidally-influenced segment has been challenging. Traditional multi-depth monitoring was done using separate monitors at different depths in the tidally-influenced segment. The monitors deployed near the surface being rapidly encrusted with barnacles and bivalves, whereas anoxic conditions near the bottom promoted corrosion of the monitors deployed at depth.

Recently, the USGS, in cooperation with the Texas Commission on Environmental Quality, using funds from Qualified Outer Continental Shelf Oil and Gas Revenues by the Coastal Impact Assistance Program, U.S. Fish and Wildlife Service, and U.S. Department of the Interior, has been able to successfully overcome these issues and monitor water quality continuously at the site for a prolonged period of time, with an initial deployment date of May 30, 2014.

For this study, the USGS has installed a vertical profiler equipped with a single monitor which allows the monitor to move up and down throughout the stratified water column, alleviating many of the historical problems. Measurements are collected at four steps with Step 1 being near the bottom of the channel and step 4 being near the surface. When the monitor is not in measurement mode, it is positioned in the anoxic zone which discourages any buildup of organisms that may have attached to the monitor in the upper part of the water column. Additionally, the periodic movement of the monitor out of the anoxic zone to take readings in the upper part of the water column reduces the likelihood of corrosion.

Arroyo Colorado at Rio Hondo

Vertical water quality profiler at U.S. Geological Survey (USGS) station 08470500 Arroyo Colorado at FM 106 at Rio Hondo, Tex.

 

Current Site Data

USGS 08470500 Arroyo Colorado at FM 106, Rio Hondo, TX