Preliminary flow records from small, mountainous channels on the Olympic
Peninsula, Washington State
Abstract
Channels and the water they convey control the spatial extent of aquatic
ecosystems and the evolution of landscapes. Over geologic time scales
(millions of years), flow rates have varied with changes in climate,
glacial extent and tectonics; however, over shorter time scales, flow
rates have remained stable enough to permit the establishment of unique
ecosystems that depend on and interact with specific flow and sediment
transport regimes. On the Olympic Peninsula, that relative stability was
altered when humans converted vast areas of old-growth forest to tree
plantations during the 20th century; however, because of the remote
location and unstable nature of the channels affected by the tree farms,
exactly how stream flow has changed is unknown. This study presents
preliminary flow observations in the Olympic Experimental State Forest
(OESF), a 110,000 ha block of public land on the west side of the
Olympic Peninsula that is presently being managed for both timber and
ecosystem values. Through repeat flow measurements and channel surveys
and the installation of pressure transducers and staff gages, we are
developing a long-term record of flow in small, (basin area 50 to 700
ha) step-pool to cascade channels that transport pulses of sediment and
violently swing between low and high flows. Preliminary flow
observations indicate that the geologic setting of the basin plays a
large role in hydrograph characteristics and that picking out a
vegetation signal in the flow record may be difficult. Nonetheless, the
long-term goal of these observations is to quantify flow trends and help
humans (The Washington State Department of Natural Resources) better
understand how past and present tree harvests on the Olympic Peninsula
may be altering natural hydrologic and geomorphic processes. Monitoring
techniques we are using to measure flow in these small, dynamic streams,
including the use of BaRatin (Le Coz et al., 2013) to develop rating
curves, are presented. Future monitoring goals and plans to use the flow
records for geomorphic and hydrologic modeling studies are also
discussed.