Evaluation of Project-Related Effects Arising From the Waneta Expansion Project on River Flows in Relation to Protection of White Sturgeon Habitat

Author: A. Lin, D. Fissel

The field monitoring program was carried out in accordance with the WEPC (2009) TOR document, Section 4.1 (Attachment A), which stated: (a) “This component of the monitoring program will be conducted during the first full spawning season following WEP commissioning in which the plant is operating. The objective will be to validate the 3D model predictions in terms of the effects of the powerplant alignment and the flow through effects of Boundary block loading on downstream flow patterns in the white sturgeon spawning area.” (b) “A boat-based Acoustic Doppler Current Profiler (ADCP) detailed flow survey will be conducted in the Columbia-Pend d’Oreille rivers confluence area from the Highway bridge over the Pend d’Oreille River downstream to the index sturgeon egg collection station at SM56D. The width of coverage would extend from the south bank of the confluence area to the interface with the southern edge of the Waneta Eddy. The flow surveys should be conducted during the spawning season at two Pend d’Oreille discharges, one where all the discharge is through WEP and one where the discharge is through both WEP and the existing Waneta (WAN) plant or spillways.” (c) “The 3D numerical velocity model will be run for these same Pend d’Oreille and Columbia River discharges for each of the cases [for which ADCP transect field measurements are available]. The ADCP flow survey data will be used to calibrate and validate the model runs with the WEP plant releases. Extensive flow surveys have previously been used to validate the 3-D numerical model for Pend d’Oreille flows through the WAN plant (and spillway). If the results of the flow surveys do not demonstrate reasonable agreement with the model velocities (agreement within to 10 to 15% or better in terms of velocity values between measured and model velocities in the ADCP survey area) and the results indicate the model needs further data to adequately represent the post-project condition, then additional surveys will be conducted. This may include both expanding the area surveyed and the range of flows.” (d) “The velocity measurement methodology will also use underwater flow meter instruments deployed in the vicinity of two of the index egg mat locations. The measurement locations selected will be in the vicinity of SM56C32, and in the vicinity of SM56C4 and SM56D. SM56C3 is within the uppermost edge of the egg deposition/incubation area and is within the direct influence of project flow effects. Sites SM56C4 and SM56D are within the direct influence of the Columbia River flows and are the location where the majority of eggs have been captured in previous spawning surveys.” (e) “The instruments will measure post-project, near-bottom velocities (nominally 0.5 m above the riverbed) continuously at sampling intervals of 5 minutes or less over the entire duration of the first full spawning and incubation season (01 June to 31 July) following commissioning of WEP.” (f) “To avoid data and equipment losses, the instruments should be retrieved with data download and then redeployed at two weekly intervals during the spawning season.” The field study portion of this evaluation was undertaken over a period of one month in July 2017. Three site visits were conducted that coincided with the high, medium, and low flow rates from the dam, which were expected at various times of the month. The study was conducted in waters near the confluence of the Columbia River and Pend d’Oreille River (Figure 2-1), with data collected by ASL and Golder field technicians. This study included two bottom mounted, 1200 kHz, Acoustic Doppler Current Profilers (ADCP), sampling continuously for the duration of the month (mooring data) and a vessel-mounted ADCP current meter collecting real time data during each site visit, which resulted in four discrete sets of 3D velocity data from the four ADCP transect surveys conducted (transect data). All data was processed and analyzed using WinRiver II, WinADCP, and ASL’s MATLAB packages. QA/QC has been conducted and the data processing report is presented below. Complete details of the methodology of the field study and summaries of the measurements obtained are presented in a data report (Clouston et al., 2017), which is included as Attachment “B” to the present report.

The project-related effects arising from the new WAX powerhouse at the junction of the Columbia and Pend d’Oreille Rivers are examined in this study. This river confluence area is important for White Sturgeon spawning and egg deposition. This evaluation study of the effects of changes in the river flow regime arising from the completion of WAX in 2015 was conducted during the 2017 White Sturgeon spawning season. The evaluation was carried out in accordance with the objectives and methods presented in the TOR document prepared in 2009 by the Waneta Expansion Power Corporation (WEPC, 2009) which arose from the EACA to confirm the environmental assessment prediction that the flow changes associated with WAX will not adversely affect the spawning habitat or spawning/incubation success.

The scientific studies conducted as part of this evaluation project involved: (a) a field monitoring program conducted in July 2017, and (b) extensive analysis and advanced 3D numerical modeling of the river flows for the June to July 2017 spawning season period.

For the TOR requirement to validate the 3D numerical velocity model under post-project conditions, the previous model developed for the EACA (ASL-COCIRM) was updated with a more advanced 3D numerical model (Delft3D) to provide detailed simulations of water velocities at near-surface and near-bottom levels. These model simulations were run for four river flow conditions encountered during July 2017 when boat-based 3D flow measurement surveys were conducted. The TOR document (WEPC, 2009) required reasonable agreement of the model with observations to within 10-15% or better. A model verification study using standard statistical model verification methods was conducted as to the relative differences between model and measured velocity variance relative to perfect agreement for which R2 is 100 percent. For the four observational data sets, the model exhibited an 11% difference in variance for near-surface velocities and an 18% difference in variance for near-bottom velocities, with a combined value of 14% for both levels. This result corresponds to an overall linear variance-averaged linear regression value, R, of 0.93 or 0.07 (7%) below a perfect score, in terms of velocity amplitude. The comparative results indicate that the model and measurements are in general agreement to better than the criteria stated in the WEPC (2009) TOR document.

Another TOR requirement was to examine the Environmental Assessment analysis based on 3D numerical modeling methods which predicted that very small changes in the downstream flow patterns would occur from the physical presence and alignment of the new WAX plant. The results of the present study confirm that the changes are very small. Under the conditions of large discharges through the WAX plant, the changes in the near-bottom speeds are negligible within the egg deposition zone downstream of egg mat site C3 and for moderate WAX discharges, the changes are much smaller. The areas in the egg deposition zone with any appreciable change due to the WAX plant represent much less than 10 percent of the egg catch per unit effort of the entire egg deposition zone, even for the large WAX discharges. Moreover, where there is an effect in terms of changed near-bottom flow speeds in the eastern limits of the egg deposition zone, the effect is to increase the flow speeds, which would be beneficial to White Sturgeon egg incubation in that it would tend to reduce egg predation by small fish that are unable to feed on eggs above the “minimum threshold” value of 0.4 m/s near bottom flow speeds (WEPC, 2007).

The TOR document (WEPC, 2009) also stipulated that detailed 3D numerical model runs would be carried out under post-project conditions for three Columbia River discharge conditions each with two or more Pend d’Oreille discharge values, including flows during Heavy Load Hours and Light Load Hours. The data from the underwater flow meters at two egg mat sites, C3 and D, would also be analysed with the actual flow discharges to develop a statistical model on the relationship between the flows and near-bottom velocities. From these methods, the derived near-bottom velocities would be computed and complied for individual egg mat sites, especially the two sites where direct measurements were obtained, in the egg deposition zone for the June and July period associated with White Sturgeon spawning. This analysis is extended to compute the near-bottom velocity distributions representative of the combined flows for all egg mats, weighted by egg catch per unit effort among the sites, in the form of histograms for June-July 2017. The near-bottom velocity distributions are realized through the use of the previous 3D modeling methods (WEPC, 2007), the updated 3D modeling methods of this this study, and the extrapolated near-bottom velocities estimated from the direct measurements at two egg mat sites (i.e., C3 and D).

The changes in the flow speed distributions relative to the egg predation thresholds for June-July 2017 between the previous model results and the updated model results represent only a small fraction of the total flow distribution. For the 0.4 m/s threshold level(i.e., the value at which small fish are generally unable to feed on White Sturgeon eggs), the differences amount to just over a 1% increase from the previous to updated flow speed values and a further increase of 2% for the mooring-derived estimates. These changes are well below the 10-15% criteria in the WEPC (2009) TOR document. Similarly, the changes for the marginal conditions of egg predation at flow speeds between 0.4 and 0.8 m/s are also quite small, with an increase of 7% from the previous model results to updated model results and a further increase of 3% to the mooring-derived flow speed estimates. Overall the total changes are less than 15% for all comparisons in the two lowest flow speed categories which confirm that the EACA predictions for the effect of the WAX plant on the flows in the egg deposition zone are accurate to within the required levels of the model to measurement uncertainties.

The project-related effects arising from the new WAX powerhouse at the junction of the Columbia and Pend d’Oreille Rivers are examined in this study. This river confluence area is important for White Sturgeon spawning and egg deposition. This evaluation study of the effects of changes in the river flow regime arising from the completion of WAX in 2015 was conducted during the 2017 White Sturgeon spawning season. The evaluation was carried out in accordance with the objectives and methods presented in the TOR document prepared in 2009 by the Waneta Expansion Power Corporation (WEPC, 2009) which arose from the EACA to confirm the environmental assessment prediction that the flow changes associated with WAX will not adversely affect the spawning habitat or spawning/incubation success.

The scientific studies conducted as part of this evaluation project involved: (a) a field monitoring program conducted in July 2017, and (b) extensive analysis and advanced 3D numerical modeling of the river flows for the June to July 2017 spawning season period.

For the TOR requirement to validate the 3D numerical velocity model under post-project conditions, the previous model developed for the EACA (ASL-COCIRM) was updated with a more advanced 3D numerical model (Delft3D) to provide detailed simulations of water velocities at near-surface and near-bottom levels. These model simulations were run for four river flow conditions encountered during July 2017 when boat-based 3D flow measurement surveys were conducted. The TOR document (WEPC, 2009) required reasonable agreement of the model with observations to within 10-15% or better. A model verification study using standard statistical model verification methods was conducted as to the relative differences between model and measured velocity variance relative to perfect agreement for which R2 is 100 percent. For the four observational data sets, the model exhibited an 11% difference in variance for near-surface velocities and an 18% difference in variance for near-bottom velocities, with a combined value of 14% for both levels. This result corresponds to an overall linear variance-averaged linear regression value, R, of 0.93 or 0.07 (7%) below a perfect score, in terms of velocity amplitude. The comparative results indicate that the model and measurements are in general agreement to better than the criteria stated in the WEPC (2009) TOR document.

Another TOR requirement was to examine the Environmental Assessment analysis based on 3D numerical modeling methods which predicted that very small changes in the downstream flow patterns would occur from the physical presence and alignment of the new WAX plant. The results of the present study confirm that the changes are very small. Under the conditions of large discharges through the WAX plant, the changes in the near-bottom speeds are negligible within the egg deposition zone downstream of egg mat site C3 and for moderate WAX discharges, the changes are much smaller. The areas in the egg deposition zone with any appreciable change due to the WAX plant represent much less than 10 percent of the egg catch per unit effort of the entire egg deposition zone, even for the large WAX discharges. Moreover, where there is an effect in terms of changed near-bottom flow speeds in the eastern limits of the egg deposition zone, the effect is to increase the flow speeds, which would be beneficial to White Sturgeon egg incubation in that it would tend to reduce egg predation by small fish that are unable to feed on eggs above the “minimum threshold” value of 0.4 m/s near bottom flow speeds (WEPC, 2007).

The TOR document (WEPC, 2009) also stipulated that detailed 3D numerical model runs would be carried out under post-project conditions for three Columbia River discharge conditions each with two or more Pend d’Oreille discharge values, including flows during Heavy Load Hours and Light Load Hours. The data from the underwater flow meters at two egg mat sites, C3 and D, would also be analysed with the actual flow discharges to develop a statistical model on the relationship between the flows and near-bottom velocities. From these methods, the derived near-bottom velocities would be computed and complied for individual egg mat sites, especially the two sites where direct measurements were obtained, in the egg deposition zone for the June and July period associated with White Sturgeon spawning. This analysis is extended to compute the near-bottom velocity distributions representative of the combined flows for all egg mats, weighted by egg catch per unit effort among the sites, in the form of histograms for June-July 2017. The near-bottom velocity distributions are realized through the use of the previous 3D modeling methods (WEPC, 2007), the updated 3D modeling methods of this this study, and the extrapolated near-bottom velocities estimated from the direct measurements at two egg mat sites (i.e., C3 and D).

The changes in the flow speed distributions relative to the egg predation thresholds for June-July 2017 between the previous model results and the updated model results represent only a small fraction of the total flow distribution. For the 0.4 m/s threshold level(i.e., the value at which small fish are generally unable to feed on White Sturgeon eggs), the differences amount to just over a 1% increase from the previous to updated flow speed values and a further increase of 2% for the mooring-derived estimates. These changes are well below the 10-15% criteria in the WEPC (2009) TOR document. Similarly, the changes for the marginal conditions of egg predation at flow speeds between 0.4 and 0.8 m/s are also quite small, with an increase of 7% from the previous model results to updated model results and a further increase of 3% to the mooring-derived flow speed estimates. Overall the total changes are less than 15% for all comparisons in the two lowest flow speed categories which confirm that the EACA predictions for the effect of the WAX plant on the flows in the egg deposition zone are accurate to within the required levels of the model to measurement uncertainties.