The Issue: Glaciers in the Hoh River watershed are expected to largely disappear by 2050, while flooding is expected to become more intense. Understanding if or how this will impact sediment transport and channel change in the watershed is relevant for salmon habitat, restoration efforts, and flood hazard management. However, there is relatively little information about historical channel elevation change and sediment delivery and transport in the watershed, making it difficult to forecast such dynamics.
How USGS will help: The USGS will utilize existing information to better understand watershed-scale sediment transport and channel change. Major analyses will include the use of repeat topographic surveys, derived from aerial imagery and lidar, to assess erosion in the glaciated headwaters back to 1939; the use of repeat aerial lidar from 2014 and 2022 to assess channel change along the mainstem rivers; and the use of annual landsat imagery back to 1984 to assess trends in planform character. Results will be synthesized with prior studies to develop a current state of science regarding sediment transport in the watershed. These results will guide future monitoring or study efforts.
Problem:
Concerns have been raised, regionally across western Washington and specific to the Hoh River watershed, that on-going glacier retreat may increase sediment delivery to downstream rivers, with subsequent impacts on channel morphology and habitat conditions. However, little is known about sediment delivery and transport in the Hoh River watershed, either in the present or recent past. It is then difficult to assess if recent glacier retreat has had an appreciable impact on the downstream river system, or if anticipated retreat is likely to do so in the coming decades.
Objectives:
The goal of this work is to improve the baseline understanding of sediment delivery and channel change in the Hoh River watershed. This work supports a larger goal of better understanding how climate trends, including glacier retreat and changing flood hydrology, have impacted the downstream river system or may impact it in the coming decades. The analyses will focus on assessing erosion and sediment delivery from recently deglaciated areas, documenting recent trends in channel elevation and planform change, and synthesizing those results and results from prior studies into an interpretive document.
Relevance and Benefits:
This work will support efforts by the Hoh Tribe to understand and manage natural resources in and around the Hoh River in the context of a changing climate. This work will also continue to build regional understandings of sediment transport and channel change in sediment-rich western Washington rivers. By providing local stakeholders with timely and relevant synthesis of complex data, this work aligns with the USGS mission to “engage with stakeholders and decision makers who rely on our science to carry out actions to mitigate riverine and coastal flooding, perform ecosystem restoration, [and] manage inland freshwater fisheries…” (USGS, 2021).
Approach:
This work will utilize existing data, and primarily existing geospatial data, to assess sediment erosion, deposition, and channel planform change in the Hoh River watershed. The work will consist of:
- An assessment of erosion and deposition in proglacial/recently deglaciated areas, using multiple elevation datasets collected between 1939 and 2022.
- An assessment of recent erosion, deposition, and planform change on the mainstem Hoh River based on repeat aerial lidar.
- An assessment of channel migration, avulsions, and planform area in the mainstem Hoh River based on annual Landsat imagery from 1984 to 2022.
Results will be synthesized along with prior studies in a peer-reviewed interpretive report summarizing the current state of knowledge on sediment delivery and transport in the Hoh River watershed, with an emphasis on the potential role of recent and forecasted climate trends.
The Issue: Glaciers in the Hoh River watershed are expected to largely disappear by 2050, while flooding is expected to become more intense. Understanding if or how this will impact sediment transport and channel change in the watershed is relevant for salmon habitat, restoration efforts, and flood hazard management. However, there is relatively little information about historical channel elevation change and sediment delivery and transport in the watershed, making it difficult to forecast such dynamics.
How USGS will help: The USGS will utilize existing information to better understand watershed-scale sediment transport and channel change. Major analyses will include the use of repeat topographic surveys, derived from aerial imagery and lidar, to assess erosion in the glaciated headwaters back to 1939; the use of repeat aerial lidar from 2014 and 2022 to assess channel change along the mainstem rivers; and the use of annual landsat imagery back to 1984 to assess trends in planform character. Results will be synthesized with prior studies to develop a current state of science regarding sediment transport in the watershed. These results will guide future monitoring or study efforts.
Problem:
Concerns have been raised, regionally across western Washington and specific to the Hoh River watershed, that on-going glacier retreat may increase sediment delivery to downstream rivers, with subsequent impacts on channel morphology and habitat conditions. However, little is known about sediment delivery and transport in the Hoh River watershed, either in the present or recent past. It is then difficult to assess if recent glacier retreat has had an appreciable impact on the downstream river system, or if anticipated retreat is likely to do so in the coming decades.
Objectives:
The goal of this work is to improve the baseline understanding of sediment delivery and channel change in the Hoh River watershed. This work supports a larger goal of better understanding how climate trends, including glacier retreat and changing flood hydrology, have impacted the downstream river system or may impact it in the coming decades. The analyses will focus on assessing erosion and sediment delivery from recently deglaciated areas, documenting recent trends in channel elevation and planform change, and synthesizing those results and results from prior studies into an interpretive document.
Relevance and Benefits:
This work will support efforts by the Hoh Tribe to understand and manage natural resources in and around the Hoh River in the context of a changing climate. This work will also continue to build regional understandings of sediment transport and channel change in sediment-rich western Washington rivers. By providing local stakeholders with timely and relevant synthesis of complex data, this work aligns with the USGS mission to “engage with stakeholders and decision makers who rely on our science to carry out actions to mitigate riverine and coastal flooding, perform ecosystem restoration, [and] manage inland freshwater fisheries…” (USGS, 2021).
Approach:
This work will utilize existing data, and primarily existing geospatial data, to assess sediment erosion, deposition, and channel planform change in the Hoh River watershed. The work will consist of:
- An assessment of erosion and deposition in proglacial/recently deglaciated areas, using multiple elevation datasets collected between 1939 and 2022.
- An assessment of recent erosion, deposition, and planform change on the mainstem Hoh River based on repeat aerial lidar.
- An assessment of channel migration, avulsions, and planform area in the mainstem Hoh River based on annual Landsat imagery from 1984 to 2022.
Results will be synthesized along with prior studies in a peer-reviewed interpretive report summarizing the current state of knowledge on sediment delivery and transport in the Hoh River watershed, with an emphasis on the potential role of recent and forecasted climate trends.