HR: 1330h
AN: H52A-1138    [PDF]
TI: Channel Initiation Processes in Basalt and Sandstone Lithologies in Southwest Washington
AU: * Jaeger, K L
EM: kljaeger@u.washington.edu
AF: College of Forest Resources University of Washington, Box 352100, Seattle, WA 98195 United States
AB: A persistent problem for managers of headwater streams has been accurately identifying where these headwater channels begin on the hillslope and determining the physical extent of the channel network. This problem is exacerbated by the relatively few published field data on both channel-head locations and initiation processes in forested landscapes of different lithologies. Several workers have presented the theory that channel-head locations are a function of an inverse slope-drainage area relationship. We hypothesized that channel-head locations in a fine-grained basalt lithology would be independent of slope. In sandstone, we expected channel-head locations to follow the inverse slope-drainage area relationship. In addition, we hypothesized that seasonal migration of surface water presence would reflect a near-surface hydrologic process whereas surface water flowing from the same location throughout the year would reflect a groundwater control. Seventy-eight channel-heads were mapped using a high resolution Global Positioning System in basalt and sandstone lithologies in southwest Washington. Source areas for these channel-heads ranged between 600 m$^{2}$ and 50,000 m$^{2}$ and local slopes ranged between 15% and 80%. The upslope extent of surface water was monitored and mapped for 14 basalt and 20 sandstone streams. Watersheds were monitored monthly from February through November 2003. Initial analyses have indicated that local slope does not correlate with channel-head locations in either basalt or sandstone lithologies. However, contributing areas with similar local slopes were significantly larger in basalt compared to certain sandstone lithologies. Observations from the surface water mapping suggest that the channel initiation processes within the basalt lithology are groundwater controlled versus the near-surface hydrologic control observed within the sandstone lithology. As a result, underlying lithology remains a major control on processes driving channel initiation and channel-head locations in high-gradient, lowland watersheds.
DE: 1824 Geomorphology (1625)
SC: Hydrology [H]
MN: 2003 Fall Meeting