Southeast Alaska Network Streamflow Monitoring

Murdoch, Craig

Freshwater: Streamflow SOUTHEAST ALASKA NETWORK – PROTOCOL DEVELOPMENT SUMMARY PARKS WHERE PROTOCOL WILL BE IMPLEMENTED: GLBA, KLGO, SITK Specific Monitoring Objectives to be Addressed by the Protocol 1. Measure and monitor streamflow for the Indian River, relative to the ability of the parkmanaged portion to provide adequate in-stream flow to support aquatic life and maintain ADF&G’s in-stream flow reservations for anadromous fish spawning, incubation, and rearing 2. Continue to monitor streamflow in the Taiya River near Skagway to establish current conditions of seasonal and annual flow patterns 3. Initiate streamflow monitoring of the Bartlett River near Gustavus to document baseline streamflow conditions 4. Identify and quantify long-term changes or trends in the annual and seasonal patterns of freshwater discharge in the Indian, Taiya, and Bartlett Rivers 5. Determine trends in chemical loads using accompanying water quality data collected under co-located monitoring of physicochemical water quality Basic Approach Streamflow is measured as discharge of water within a river channel past a specific point for a given time interval. Streamflow gaging stations typically consist of a pressure sensing transducer fixed to the stream bed at a known elevation. The transducer measures the elevation of the stream’s water surface, which is recorded by a data logger. A relation between water surface elevation (stage) and discharge is established by measuring streamflow over a range of stage. Once this relationship is well defined, a rating curve can be developed and streamflow can be computed from the stage data and rating curve. Periodic streamflow measurements are required to adjust for changes in channel morphology, debris, and aquatic vegetation growth, all of which may significantly alter the relation between stage and discharge. In order to keep discharge estimates accurate, six to nine discharge measurements spanning the full range of flow should be taken each year. Moderate and low flows can be measured by wading using current meters and top setting wading rods, however, measuring high flows or flood flows is essential to development and refinement of rating curves. These measurements will need to be conducted by boat or from bridges using conventional current meters in combination with a bridge crane, reel, and sounding weight or using acoustic Doppler current profilers (ADCP). The ADCP is capable of measuring discharge from a moving boat and would be essential to making discharge measurements when no bridge is available from which to suspend a traditional current meter. The USGS has developed extensive protocols for making discharge measurements and operating stream gages (Rantz et al. 1982a, 1982b). Protocol developed for SEAN streamflow monitoring will draw from these protocols. Principal Investigators and NPS Lead U.S. Geological Survey, Juneau and Anchorage offices SITK: Geoffrey Smith GLBA: Chad Soiseth KLGO: Dave Schirokauer Development Schedule, Budget, and Expected Interim Products Optimally, streamflow monitoring should be continuous. Continuation of streamflow monitoring on streams previously gaged by the USGS (Indian River and Taiya River) is recommended for the following reasons: 1) stage/discharge ratings may already be available 2) the value of streamflow data increases with longer time series, and 3) the location of these gages facilitates frequent visits, which are essential to producing accurate and complete data sets. An additional gage will be installed on the Bartlett River near Gustavus.

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