Pysht River Floodplain Habitat Inventory and Assessment
The Pysht River Floodplain Habitat inventory and assessment project was completed February 2006. This study assessed floodplain habitats (including off-channel and estuary habitats) of the Pysht River between river mile 0 and 11.5 to evaluate impacts to salmon habitat productivity within the basin. The assessment was developed to guide restoration efforts on the Pysht River floodplain through the development of a prioritized restoration list. Road and railroad grade construction, road maintenance and protection (e.g., rip-rap), channelization, channel relocation, logging, in channel wood removal, dredging, homesteading, agricultural development, wetland filling, and rural development have all contributed to floodplain habitat alterations in the Pysht Watershed. A total of 130 floodplain tributary habitat segments were identified in 29 tributary subbasins. Of these, 128 (98.5%) were identified as providing habitat for anadromous fish or having the potential to provide habitat.
Neary 62% of the habitat segments inventoried were classified as off-channel/over-wintering habitats. Habitat types were unevenly distributed both longitudinally and horizontally along the river valley. Higher gradient habitats were almost entirely identified in the upper watershed and along the margins of the floodplain. Nearly 80% of all low gradient, off-channel habitat entered the mainstem below river mile 5.0. A total of 29 of the 37 (78%) culverts inventoried were classified as partial or complete fish barriers. Only 9 (24%) of the culverts were classified as 100% passable and of these, only four were considered properly functioning. In all, 34 out of 37 (92%) of the culverts inventoried were either partial or complete fish barriers and/or not properly functioning (undersized, blocking tidal exchange, or preventing adequate sediment and lwd transport).
Culverts were estimated to represent barriers (partial or total) to nearly 53% of the total length of floodplain habitat. Fish-bearing (or potentially fish-bearing) wetland areas upstream of culvert blockages were also examined by acreage. A total of 74.9 acres of fish-bearing wetlands were identified along the Pysht River floodplain. Only 29% of these habitats were classified as 100% accessible to fish. Other habitat alterations were identified as a result of poorly designed and placed culverts. Several culverts that were undersized and improperly placed acted to alter sediment and LWD transport, disconnect the tidal prism of the lower river from floodplain tributaries, cause downstream erosion through accelerated velocities and outfall drops, and cause backwater flooding and habitat disconnection.
Encroachment of roads was determined to be the greatest floodplain impact because roads prevent lateral migration of the river and reduce riparian influence (LWD recruitment, shade, bank protection). Within the first 30 meters of the Pysht River's banks, road represented 78% of the total length of floodplain encroachment. State Route 112 contained the greatest length of stream parallel road network and contained more stream parallel length than all roads combined in all four encroachment zones evaluated. Road construction and protection, channelization, and wood removal have affected the river's ability to migrate across the valley, hence decreasing the river's ability to form off-channel habitats now and into the future. While rates of channel migration are not currently available for the Pysht River a review of the 1951 aerial photos compared to 2003 aerial photos indicates that the channel has not undergone drastic lateral migration. A series of historical impacts were identified in the lower river and estuary. These were associated with past water based log transport and include dredging, wetland filling, and disconnection (associated with the disposal of dredge spoils), channelization, and road construction. Restoration projects were identified in all subbasins and include correction of barriers, road relocation, riparian planting, and LWD additions. A prioritized list of projects was developed based upon the amount of habitat improved, cost, and feasibility.
Neary 62% of the habitat segments inventoried were classified as off-channel/over-wintering habitats. Habitat types were unevenly distributed both longitudinally and horizontally along the river valley. Higher gradient habitats were almost entirely identified in the upper watershed and along the margins of the floodplain. Nearly 80% of all low gradient, off-channel habitat entered the mainstem below river mile 5.0. A total of 29 of the 37 (78%) culverts inventoried were classified as partial or complete fish barriers. Only 9 (24%) of the culverts were classified as 100% passable and of these, only four were considered properly functioning. In all, 34 out of 37 (92%) of the culverts inventoried were either partial or complete fish barriers and/or not properly functioning (undersized, blocking tidal exchange, or preventing adequate sediment and lwd transport).
Culverts were estimated to represent barriers (partial or total) to nearly 53% of the total length of floodplain habitat. Fish-bearing (or potentially fish-bearing) wetland areas upstream of culvert blockages were also examined by acreage. A total of 74.9 acres of fish-bearing wetlands were identified along the Pysht River floodplain. Only 29% of these habitats were classified as 100% accessible to fish. Other habitat alterations were identified as a result of poorly designed and placed culverts. Several culverts that were undersized and improperly placed acted to alter sediment and LWD transport, disconnect the tidal prism of the lower river from floodplain tributaries, cause downstream erosion through accelerated velocities and outfall drops, and cause backwater flooding and habitat disconnection.
Encroachment of roads was determined to be the greatest floodplain impact because roads prevent lateral migration of the river and reduce riparian influence (LWD recruitment, shade, bank protection). Within the first 30 meters of the Pysht River's banks, road represented 78% of the total length of floodplain encroachment. State Route 112 contained the greatest length of stream parallel road network and contained more stream parallel length than all roads combined in all four encroachment zones evaluated. Road construction and protection, channelization, and wood removal have affected the river's ability to migrate across the valley, hence decreasing the river's ability to form off-channel habitats now and into the future. While rates of channel migration are not currently available for the Pysht River a review of the 1951 aerial photos compared to 2003 aerial photos indicates that the channel has not undergone drastic lateral migration. A series of historical impacts were identified in the lower river and estuary. These were associated with past water based log transport and include dredging, wetland filling, and disconnection (associated with the disposal of dredge spoils), channelization, and road construction. Restoration projects were identified in all subbasins and include correction of barriers, road relocation, riparian planting, and LWD additions. A prioritized list of projects was developed based upon the amount of habitat improved, cost, and feasibility.