HR: 14:00h
AN: B53B-03    [Abstracts]
TI: The effect of vegetation and beaver dams on geomorphic recovery rates of incised streams in the semi-arid regions of the Columbia River basin, USA.
AU: * Pollock, M
EM: michael.pollock@noaa.gov
AF: NOAA Northwest Fisheries Science Center, 2725 Montlake Blvd E, Seattle, WA 98112 United States
AU: Beechie, T
EM: tim.beechie@noaa.gov
AF: NOAA Northwest Fisheries Science Center, 2725 Montlake Blvd E, Seattle, WA 98112 United States
AU: Jordan, C
EM: chris.jordan@noaa.gov
AF: NOAA Northwest Fisheries Science Center, 2725 Montlake Blvd E, Seattle, WA 98112 United States
AB: Channel incision is a common occurrence in semi-arid regions of the Columbia River basin and throughout the world, where a fragile balance between climate, vegetation and geology makes channels susceptible to changes in hillslope erosion, stream discharge and sediment yield. Incision is defined as a rapid downcutting and lowering of the stream bed such that it reduces the frequency and duration of flooding onto the adjacent floodplain. We are studying the feasibility of restoring incised streams throughout the interior Columbia River basin. We hypothesize that under proper land use management, it is possible for them to aggrade such that they reconnect to their former floodplains within relatively short time frames. Theoretical and empirical evidence suggests that over decadal time scales, changes to land management that excludes grazing and allows riparian vegetation to become established can cause significant fill within the incised valleys. Preliminary modeling suggests that factors most affecting the length of time for an incised valley to completely aggrade and reconnect to its pre-incision floodplain are the depth of the incision, sediment production in the watershed, the amount and type of riparian vegetation, and the extent of beaver dam construction. While most natural resource and fisheries managers are aware of widespread incision throughout the Columbia River basin, the extent of incision within the range of the Pacific salmon is largely undocumented. However, we do know many incised streams that historically supported salmon no longer do so, and that habitat conditions are severely degraded in these incised streams. The historical record shows that numerous salmon-bearing streams in the semi-arid region of the interior Columbia River basin once contained narrow and deep, slowly meandering channels lined with cottonwoods, willows and/or sedges, contained numerous beaver dams, contained abundant and easily accessible off-channel habitat on the floodplain and had good flow and cool temperatures throughout most of the year. Today most of these streams are incised and contain little or no riparian vegetation or beaver dams. Stream temperatures are high and flow is ephemeral. Incision is thought to have lowered stream-adjacent water tables, causing both the loss of riparian vegetation and the increase in stream temperature. Many of these streams no longer support fish populations. We hypothesize that if incised streams were restored by creating conditions such that they could aggrade and reconnect to their former floodplains, that habitat conditions would be sufficient to again support salmon populations, and that this would greatly expand their range throughout much of the Columbia River basin.
DE: 1809 Desertification
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
DE: 1829 Groundwater hydrology
DE: 1851 Plant ecology
SC: Biogeosciences [B]
MN: 2005 Joint Assembly