Oregon Water Quality Index Report for South Coast Basin

Water Years 1986-1995

Land use and water quality conditions in the South Coast basin varies more than the Mid Coast basin but less than the North Coast basin. Of the monitored subbasins, the Coquille subbasin is the largest, most populated, most utilized for agriculture, and most water quality limited. During the period of Water Years 1986-1995, water quality data were collected by the DEQ Laboratory periodically in the Coquille subbasin from 1986-1991 to establish the Coquille River Total Maximum Daily Load (TMDL). Routine ambient monitoring of South Coast basin streams in Table 1 began in 1992. Comparing minimum seasonal Oregon Water Quality Index (OWQI) values (Table 1), water quality ranges from poor (Sixes River site) to excellent (Winchuck River site).

Water quality is commonly impacted by the introduction of organic matter to streams. The presence of organic matter increases biochemical oxygen demand, which means less dissolved oxygen is available for aquatic life. The introduction of untreated animal or human waste increases the possibility of bacterial contamination of water, increasing the risk of infection to swimmers. Eutrophication is the process of enrichment of water with nutrients, mainly nitrogen and phosphorous compounds, which results in excessive growth of algae and nuisance aquatic plants. It increases the amount of organic matter in the water and also increases pollution as this matter grows and then decays. Employing the process of photosynthesis for growth, algae and aquatic plants consume carbon dioxide (thus raising pH) and produce an overabundance of oxygen. At night the algae and plants respire, depleting available dissolved oxygen. This results in large variations in water quality conditions that can be harmful to other aquatic life. While natural sources of nutrients can influence eutrophication, the introduction of nutrients strengthens the process. Sources of nutrients include wastewater treatment facility discharge and faulty septic systems, runoff from animal husbandry, fertilizer application, urban sources, and erosion. High water temperatures compound the decline in water quality by causing more oxygen to leave the water and by increasing the rate of eutrophication. Removal of streamside vegetation, among other factors, influences high stream temperature and, via erosion, increases sedimentation of streams.

Table 1. Seasonal Average OWQI Results for the South Coast Basin (WY 1986-1995)

Summer: June - September; FWS ( Fall, Winter, & Spring): October - May
Scores - Very Poor: 0-59, Poor: 60-79, Fair: 80-84, Good: 85-89, Excellent: 90-100

Coquille Subbasin

The Coquille subbasin is used for logging, agriculture, and population centers supporting these uses. Non-point sources such as erosion, field run-off, and faulty septic systems and point sources including sewage treatment plant (STP) bypass and log ponds contribute to water quality impairment. The Coquille River TMDL addresses these concerns.

The South Fork Coquille River at Broadbent is the monitoring site furthest up-basin. This site is approximately eighteen river miles downstream from the nearest significant point source, the Powers STP. Water quality impacts occur mainly during the high flow seasons of fall, winter, and spring, when heavy precipitation leads to runoff and erosion of rural lands, increased leaking of faulty septic systems, and possible overflow conditions at the STP. High concentrations of fecal coliforms, total phosphates, and total solids present the greatest demands on water quality at this monitoring site. High temperatures occasionally limit water quality in the summer. Moderately high levels of biochemical oxygen demand occur throughout the year. These results indicate the introduction of organic matter and human or animal waste to the river. On the average, OWQI values are good in the summer but fair in the fall, winter, and spring (Table 1).

The Middle Fork Coquille River enters the South Fork approximately 4.5 miles from its confluence with the North Fork. The Middle Fork Coquille supports a small human population and has no significant point source of pollution. Subsequently, water quality in the Middle Fork is slightly better than in the South Fork. The Middle Fork Coquille River at Oregon Highway 42 near the river mouth does occasionally experience high levels of fecal coliforms, total phosphates, and nitrate nitrogen during high flows and high temperatures during low flows. High levels of total solids and biochemical oxygen demand accompany these impacts throughout the year. High levels of nutrients (phosphates and nitrogens) contribute to eutrophication in the river. On the average, OWQI values are good in the summer and fair in the fall, winter, and spring (Table 1).

The North Fork Coquille River monitoring site is situated at Oregon Highway 42 near the river mouth. This portion of the river receives inputs from the North and East Forks, from the immediately surrounding agricultural area, and from tidal influences. The Myrtle Point STP is located on the South Fork Coquille River approximately one river mile upstream of the confluence of the South and North Forks. It is possible that the Myrtle Point STP could influence water quality at the North Fork Coquille River monitoring site under the right tidal conditions. Water quality impacts at this site include high levels of fecal coliforms, total solids, nitrate nitrogen, total phosphates and biochemical demand during high flows. Occasionally during low flow, very high levels of biochemical oxygen demand contribute to low levels of dissolved oxygen. OWQI values are fair in the summer and poor in the fall, winter, and spring (Table 1).

Water quality impacts are even more complicated at the next monitoring site, the mainstem Coquille River at Strudivant Park Dock. This site is situated downstream of agricultural non-point sources of concern, log ponds, and the Coquille STP outfall. Tides also influence water quality here. High levels of fecal coliform, total solids, and total phosphates are accompanied with moderately high levels of ammonia and nitrate nitrogens and biochemical oxygen demand throughout the year. During periods of low flow, high temperatures combined with high levels of oxygen demand lead to the depletion of available dissolved oxygen. On the average, OWQI values are poor throughout the year (Table 1).

Sixes Subbasin

The Sixes subbasin includes the Sixes and Elk Rivers. Water quality conditions at the Sixes River at US Highway 101 are generally very good or excellent. However, during periods of heavy precipitation and high flows, high concentrations of total phosphates, total solids, and biochemical oxygen demand, indicating erosion and field runoff, inhibit water quality. Summer OWQI values show excellent water quality on the average, while fall, winter, and spring can be poor, especially during heavy precipitation (Table 1).

Elk River at US Highway 101 shows the same impacts as Sixes River, albeit at a smaller scale. Fecal coliform, total phosphates, and biochemical oxygen demand impact water quality during periods of heavy precipitation. On the average, OWQI values are excellent in the summer and good in the fall, winter, and spring (Table 1).

Chetco Subbasin

The Chetco subbasin includes the Pistol, Chetco, and Winchuck Rivers. These rivers experience the same impacts on water quality as the Sixes and Elk Rivers. The influence of heavy precipitation on water quality on the monitored sites in the Chetco subbasin decreases from north to south.

The Pistol River at Pistol River Loop Road experiences high levels of total phosphates, total solids, biochemical oxygen demand, and fecal coliform loading the river during heavy precipitation. This could be the result of field run-off and erosion. OWQI values for Pistol River are good in the summer, on the average, and poor in the fall, winter, and spring (Table 1).

The Chetco River at the USGS Gage Station (river mile 10.8) is also impacted during heavy precipitation by high total phosphates, biochemical oxygen demand, and total solids. On the average, OWQI results are excellent in the summer and poor in the fall, winter, and spring (Table 1).

In terms of streams throughout the state regularly monitored by the DEQ Laboratory, the Winchuck River is second in quality only to the Minam River. Slight elevations in total phosphates and total solids occur during periods of precipitation, but OWQI results show that the Winchuck River upstream of Highway 101 is excellent throughout the year (Table 1).

References

Oregon Department of Environmental Quality, Water Quality Division, 1988. 1988 Oregon Statewide Assessment of Nonpoint Sources of Water Pollution. Portland, Oregon.

Oregon Department of Environmental Quality, Water Quality Division, 1988. Oregon's 1988 Water Quality Status Assessment Report (305 (b) Report). Portland, Oregon.

Oregon Department of Environmental Quality, Water Quality Division, 1990. Oregon's 1990 Water Quality Status Assessment Report (305 (b) Report). Portland, Oregon.

Oregon Department of Environmental Quality, Water Quality Division, 1992. Oregon's 1992 Water Quality Status Assessment Report (305 (b) Report). Portland, Oregon.

Oregon Department of Environmental Quality, Water Quality Division, 1994. Oregon's 1994 Water Quality Status Assessment Report (305 (b) Report). Portland, Oregon.

Written by Curtis Cude, Oregon Department of Environmental Quality, Laboratory Division