Water temperatures in some areas of the Upper Chehalis River Watershed (WRIA 23) have become so warm during June and July that it can not support all the life-cycle stages of cold water fish (salmon, steelhead, and trout). In some cases, the temperatures are so warm that they can be lethal for these species.
Under the Clean Water Act, every state has its own standards designed to protect water quality. Most of the upper Chehalis River is classified in the State Water Quality Standards as Class "A" waters. Class "A" waters should support migration, rearing, and spawning of cold water fish species. Temperatures in these waters should not be warmer than 18.0 degrees C (64.4 degrees Fahrenheit). When natural river conditions cause the temperature to exceed 18.0 degrees C, no temperature increases due to human activities can be allowed that will raise the receiving water temperature by greater than 0.3 degrees C.
Water quality monitoring shows that temperature criteria are exceeded in at least 19 segments of 9 different streams in the upper Chehalis River watershed. The following streams are included on Washington State's 1998 Section 303(d) list of impaired waters because portions of them violate the temperature criteria of the State Water Quality Standards:
Temperature data collected in the Upper Chehalis River Basin show a definite pattern of seasonal variation. Most of the year temperature criteria are met. The critical period for temperature in the Upper Chehalis River Basin is in the months of June and July.
When a lake, river or stream fails to meet water quality standards the Federal Clean Water Act requires that the state place the water body on a list of "impaired" waters, and that an analysis called a Total Maximum Daily Load (TMDL) be prepared. A TMDL evaluates the water quality problem and the pollutant sources that cause the problem. The TMDL determines the amount of a given pollutant that can be discharged to the water body and still meet standards. The goal of a TMDL is to ensure the impaired water will attain water quality standards so that is supports designated beneficial uses.
THE UPPER CHEHALIS RIVER TEMPERATURE TMDL
The Upper Chehalis River TMDL has been developed for heat (i.e. incoming solar radiation). Heat is considered a pollutant under Section 502(6) of the Clean Water Act. Heat generated by the amount of solar radiation from sunlight reaching the stream provides energy that raises water temperatures. A decrease in shade is the result of a lack of adequate riparian vegetation and causes a subsequent increase in solar radiation and thermal load. Human activities that contribute to degraded riparian vegetation conditions include agricultural activities, residential and urban development, and silvicultural activities. The Upper Chehalis River temperature TMDL establishes goals for a shade as a surrogate measure for incoming solar radiation. This study found over 30% of riparian vegetation has been lost or reduced in the upper basin.
Two other factors that influence the distribution of heat are assessed in the study: instream flow and channel morphology. Low flows may contribute to high temperatures by reducing the volume of water that can absorb incoming heat. Channel shape and condition may also influence heat distribution. With increased sediment loads, stream channels may become wider and shallower allowing more thermal radiation to be absorbed by the water surface.
The Upper Chehalis River system has had base flows established for the protection of instream uses (e.g. salmonid habitat) at 14 locations by state rule. Recent assessments of compliance with that rule show that streams are not meeting these flows between 33 to 77 days per year. The water rights and claims exceed the critical low flow conditions (7Q10) by 400%.
Both of the additional factors evaluated, instream flow and channel morphology, had an important effect on stream temperatures. However, neither will be used in setting load allocations. The significant issue of over-allocation of the instream flow resources will be difficult to solve short of court adjudication. The stream morphology that is not considered good for anadromous fish habitat cannot be quantitatively linked to a manageable pollutant as required by EPA guidance for TMDLs. Even if the sediment load were reduced enough to narrow the stream channel width, riparian vegetation would have to be introduced and grown to existing heights to achieve the results obtained by the modeling analysis.
It has been shown that managing riparian shading alone can achieve stream temperature standards. Therefore, the load allocation and implementation strategy will be based on restoring and maintaining riparian shade. If a future assessment can show a quantifiable link between sediment load and stream channel morphology, the TMDL may be revised to trade allocations between the shade measure established and sediment management practices. Likewise, if water rights can be returned to the river through conservation or adjudication, the TMDL may be revised to trade allocations between the shade measure established and the higher flows.
IMPLEMENTATION STRATEGY
The modeling results and the loading capacity show that existing shade levels are not sufficient to meet stream temperature standards throughout the Upper Chehalis River Basin. First, the existing riparian vegetation must be maintained. In addition, some sort of restoration will be needed to achieve the shade levels set as load allocations.
The passive restoration strategy involves the protection of existing riparian areas as reserves combined with some silvicultural work to reach the existing vegetative potential rapidly. The strategy would be to allow existing species to attain old growth stage without species replacement. For existing confers at an average site index of 100, that would be a Western Hemlock dominated forest of 200 years with a height of 125 feet. For existing hardwoods at an average site index of 100, that would be a Red Alder dominated forest of 60 years with a height of 100 feet. The results of a passive restoration approach would be that all listed segments would meet temperature standards by the time existing vegetation reached old growth stage.
Even though passive restoration has been shown to eventually meet standards, active tree planting must still be conducted so that all riparian corridors have riparian shade. The model assumed that non-forested land uses had a 50% density of hardwoods. The passive restoration assumed that this increased to 85% density. This means that reaches that are now devoid of trees should be planted to help achieve the higher density for these lands.
The public is invited to comment on this draft study until June 4, 1999. An electronic copy of the draft Upper Chehalis River Basin Temperature TMDL may be obtained by E-mailing Kahle Jennings at kjen461@ecy.wa.gov. To obtain a paper copy of the TMDL, contact Cathy Brockmann at 407-6270. An online copy is available at: the Chehalis River Council internet site.
Written comments should be postmarked no later than June 4, 1999 and mailed to:
Kahle Jennings
Department of Ecology, Southwest Regional Office
P.O. Box 47775
Olympia, WA 98504-7775
Comments will also be accepted through electronic mail at kjen461@ecy.wa.gov OR send online mail right now to: Kahle Jennings through June 4, 1999.
For further information call (360) 407-6269
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