Lower Columbia River Indian Eddy Dredging Definition Phase Task 1 Summary Report, CLBWORKS-20
Author: B. Hildebrand
The Definition Phase was divided into two tasks. Task 1 included data collection (bathymetric surveys), data analysis (including comparison to bathymetric data collected in 2008), and reporting. Task 2 will include the production of meeting visuals, stakeholder engagement, and the recording stakeholder meeting minutes if required. Task 1 had three distinct objectives: 1) Conduct bathymetric surveys in 2015 to obtain updated topographic profiles of the study area. 2) Compare current survey data to data collected during previous surveys in April and June 2008 (NHC 2009). 3) Assess changes in navigable water depth between surveys, and identify if there is a need to conduct dredging operations to address safety concerns to public use of the study area.
The comparison of the data between bathymetric surveys shows that the majority of the eddy had similar substrate elevations (range of not greater than ±0.25 m; Figure 3). However, consistently higher elevations were documented in the northern section of the eddy. Compared to the previous surveys, the majority of areas on the north shore exhibited between 0.25 and 0.50 m of deposition. Small amounts of area along the north shore exhibited up to 1 m of sediment deposition. This indicated that sediment from the northern banks are being mobilized and deposited immediately to the south in the deeper areas of the eddy. The island near the center of the eddy exhibited movement eastward (i.e., closer to the left downstream bank) by approximately 20 m.
The comparison of the two bathymetric surveys was also intended to identify potential entrance and egress issues associated with navigation of vessels using the Indian Eddy boat lunch location. The comparison indicated that the elevation of the access into the eddy through its downstream end remained relatively stable between 2008 and 2015, with changes not greater than ±0.25 m. Similar to the northern portions of the eddy, the upstream portion of the entrance into the eddy shows sediment deposition of up to 0.5 m, with small sections showing areas with depositions of up to 1 m.
At the time of survey, the river banks above the water surface show lower elevations compared to the 2008 survey, and indicate that the banks were subject to erosion between 2008 and 2015. Within the eddy limit, the total net volume of sediments that were deposited between the two surveys is 1536 m3, while the total net volume of sediments eroded was 4732 m3. This resulted in a net erosion of 3197 m3 of sediment.
The comparison of the data between bathymetric surveys shows that the majority of the eddy had similar substrate elevations (range of not greater than ±0.25 m; Figure 3). However, consistently higher elevations were documented in the northern section of the eddy. Compared to the previous surveys, the majority of areas on the north shore exhibited between 0.25 and 0.50 m of deposition. Small amounts of area along the north shore exhibited up to 1 m of sediment deposition. This indicated that sediment from the northern banks are being mobilized and deposited immediately to the south in the deeper areas of the eddy. The island near the center of the eddy exhibited movement eastward (i.e., closer to the left downstream bank) by approximately 20 m.
The comparison of the two bathymetric surveys was also intended to identify potential entrance and egress issues associated with navigation of vessels using the Indian Eddy boat lunch location. The comparison indicated that the elevation of the access into the eddy through its downstream end remained relatively stable between 2008 and 2015, with changes not greater than ±0.25 m. Similar to the northern portions of the eddy, the upstream portion of the entrance into the eddy shows sediment deposition of up to 0.5 m, with small sections showing areas with depositions of up to 1 m.
At the time of survey, the river banks above the water surface show lower elevations compared to the 2008 survey, and indicate that the banks were subject to erosion between 2008 and 2015. Within the eddy limit, the total net volume of sediments that were deposited between the two surveys is 1536 m3, while the total net volume of sediments eroded was 4732 m3. This resulted in a net erosion of 3197 m3 of sediment.
Resources Data:
Name: CLBWORKS-20-YR1-2016-02-29
Format: PDF
URL: https://www.bchydro.com/content/dam/BCHydro/customer-portal/documents/corporate/environment-sustainability/water-use-planning/southern-interior/clbworks-20-yr1-2016-02-29.pdf
Additional Info
Study Years: 2015
Published: 2016
Lower Columbia River Indian Eddy Dredging Definition Phase Task 1 Summary Report, CLBWORKS-20
Author: B. Hildebrand
Tags: Bathymetry, CLBWORKS20, Dredging, Erosion, Indian Eddy, Lower Columbia River, Monitoring Recommendations, Physical Works, Restoration Recommendations, Sediment Accumulation, WLR
The Definition Phase was divided into two tasks. Task 1 included data collection (bathymetric surveys), data analysis (including comparison to bathymetric data collected in 2008), and reporting. Task 2 will include the
production of meeting visuals, stakeholder engagement, and the recording stakeholder meeting minutes if required.
Task 1 had three distinct objectives:
1) Conduct bathymetric surveys in 2015 to obtain updated topographic profiles of the study area.
2) Compare current survey data to data collected during previous surveys in April and June 2008 (NHC 2009).
3) Assess changes in navigable water depth between surveys, and identify if there is a need to conduct dredging operations to address safety concerns to public use of the study area.
Summary
The comparison of the data between bathymetric surveys shows that the majority of the eddy had similar substrate elevations (range of not greater than ±0.25 m; Figure 3). However, consistently higher elevations were documented in the northern section of the eddy. Compared to the previous surveys, the majority of areas on the north shore exhibited between 0.25 and 0.50 m of deposition. Small amounts of area along the north shore exhibited up to 1 m of sediment deposition. This indicated that sediment from the northern banks are being mobilized and deposited immediately to the south in the deeper areas of the eddy. The island near the center of the eddy exhibited movement eastward (i.e., closer to the left downstream bank) by approximately 20 m.
The comparison of the two bathymetric surveys was also intended to identify potential entrance and egress issues associated with navigation of vessels using the Indian Eddy boat lunch location. The comparison indicated that the elevation of the access into the eddy through its downstream end remained relatively stable between 2008 and 2015, with changes not greater than ±0.25 m. Similar to the northern portions of the eddy, the upstream portion of the entrance into the eddy shows sediment deposition of up to 0.5 m, with small sections showing areas with depositions of up to 1 m.
At the time of survey, the river banks above the water surface show lower elevations compared to the 2008 survey, and indicate that the banks were subject to erosion between 2008 and 2015. Within the eddy limit, the total net volume of sediments that were deposited between the two surveys is 1536 m3, while the total net volume of sediments eroded was 4732 m3. This resulted in a net erosion of 3197 m3 of sediment.