RESEARCH POSTER PRESENTATION DESIGN © 2015
www.PosterPresentations.com
This research was supported by the
Jamie Cassels Undergraduate Research Awards, University of Victoria
Supervised by Dr. Shannon Fargey, Department of Geography
Modelling Fluvial Discharge and Sediment Transport of the Skeena Watershed
Water & Sediment
Discharge
Elevation
Temperature
Groundwater
Vegetation
River Profile
Glaciers
Sediments &
Lithology
Precipitation
Model Inputs
Motivation and Research Questions
Results and Discussion
References
Methods
In order to address a gap in knowledge on the sediment deposition occurring at the mouth of the SR, the model Hydrotrend was used to estimate sediment load and river discharge at the SK mouth over a thirty year period (1981-2010).
Modelling by Subbasin: Required inputs for the model were retrieved,
calculated, and estimated based on a number of open source data and available publications (please contact me for a data reference list). The Skeena watershed was modelled up to the Usk hydrometric station in order for the discharge values computed by the model to be compared with the available measured hydrometric discharge data. Usk hydrometric data was extracted from the Environment and
Climate Change Canada Historical Hydrometric Data website in January, 2018 (https://wateroffice.ec.gc.ca/mainmenu/historical_data_index_e.html).
Sensitivity Analysis: A sensitivity analysis was conducted on the subbasin 2
data in order to decipher the impact of different variables on the discharge output. After making appropriate corrections to inputs, model accuracy was assessed through a two sample z-test of the means. Differences in monthly
discharge were plotted and discussed between the model and measured data.
The Entire Skeena Watershed: New inputs were calculated and entered into
hydrotrend for the entire watershed to predict the discharge at the river mouth.
Anthropogenic
Influences
Reservoirs
Beebe, S. (2008). Aerial view of the Skeena River. Retrieved February, 2018, from https://commons.wikimedia.org/wiki/File:Skeena_River1.jpg (Originally photographed 2008, July 31)
Bhangu, I., & Whitfield, P. H. (1997). Seasonal and long-term variations in water quality of the Skeena River at Usk, British Columbia. Water research, 31(9), 2187-2194. Gottesfeld, A., & Rabnett, K. A. (2008). Skeena river fish and their habitat. Portland, OR; Hazelton, BC; Ecotrust.
Hoos, L. (1975). The Skeena River Estuary: Status of Environmental Knowledge to 1975. Special Estuary Series 3; Environment Canada. Kelson, J. (2012). 2011 Skeena Estuary Study (Rep.). Retrieved January 20, 2017.
Kettner, A. J., & Syvitski, J. P. (2008). HydroTrend v. 3.0: a climate-driven hydrological transport model that simulates discharge and sediment load leaving a river system. Computers & Geosciences, 34(10), 1170-1183.
Levin, L. A., Boesch, D. F., Covich, A., Dahm, C., Erséus, C., Ewel, K. C., ... & Strayer, D. (2001). The function of marine critical transition zones and the importance of sediment biodiversity. Ecosystems, 4(5), 430-451.
Milliman, J. D., & Meade, R. H. (1983). World-wide delivery of river sediment to the oceans. The Journal of Geology, 91(1), 1-21.
Natural Resource Canada. (2016, January 25). [National Hydro Network (NHN)- Geobase Series]. Open Government License-British Columbia Data. Retrieved from: https://open.canada.ca/data/en/dataset/a4b190fe-e090-4e6d-881e-b87956c07977
Walters, C.J., Lichatowich, J.A., Peterman, R.M. and Reynolds, J.D. (2008). Report of the Skeena Independent Science Review Panel. A report to the Canadian Department of Fisheries and Oceans and the British Columbia Ministry of the Environment. May 15, 2008
Figure 3 was created in ArcMap using ESRI Imagery and waterbodies & boundaries modified from NRCAN’s National Hydro Network- Geobase Series (2016).
Model Inputs Figure 2
Background
➢ Sediments are a crucial component to the aquatic ecosystem of estuaries, as they
influence the biotic and abiotic exchanges and morphology (Levin et al., 2001). The Skeena River (SR) deposits millions of tones of sediment into the Skeena
estuary (SE) (Kelson, 2012). The Skeena is an undammed river that originates in the Interior Mountains, flows through the Hazelton and Coast Ranges, and
empties into the Pacific Ocean near Chatham Sound (Walters et al., 2008). The Skeena estuary, from the Skeena delta to Chatham Sound, contains pockets of
sheltered water where sedimentation occurs creating ideal conditions for eel grass growth (Hoos, 1975). Eel grass areas provide protected and nutrient rich habitats for fish and waterfowl (Hoos, 1975).
➢ Peak snowmelt and rainfall events flush sediments, carbon, and other nutrients through the watershed (Bhangu and Whitfield). Other ions, introduced through the contribution of ground water, are diluted
The Hydrotrend Model
➢ Hydrotrend is a C numerical model used to
estimate sediment load and water discharge at a river outlet based on inputs provided by the user that describe the watersheds physical properties and climate (Kettener &Syvistki, 2008).
➢ Discharge calculations are based on snow
melt/storage, glacier melt, surface runoff, and groundwater contribution (Kettner & Syvitski,
2008). Sediment load is determined by the total drainage area, discharge, relief, temperature,
lithology, and anthropogenic influence on soil erosion (Kettner & Syvitski, 2008).
➢ Motivation: To better assess water availability, flood events, erosion and
deposition, changes in water balance, and the ecological implications of change in river inputs to the estuary, it is necessary to be aware of changes in water and sediment discharge. Currently, there is a limited record of the sediment load and discharge transported by the Skeena into the estuary making it difficult to assess any long term changes (Gottesfeld & Rabnett, 2008).
➢ Can a numerical prediction model be used to estimate sediment load and river
discharge in the Skeena River with the amount of data that is currently available? ➢ What are the implications of Skeena River sediment load and discharge on the
estuary and how might discharge values change based on watershed conditions?
➢ Although, the data was modelled over thirty years, the results are displayed below (figure 4, 5, & 6) are for a ten or five year periods in order to make them more legible. At the Skeena delta, mean monthly discharge was calculated by the hydrotrend model as 1455.82 m^3/s with a suspended sediment load of 855.24 kg/s and bedload of 224.82 kg/s (figure 5). A substantial portion of the sediment load (730.77 kg/s ) was attributed to glacier sediment flux. There is no data directly at the river mouth to compare predicted values to (figure 4).
Instead, a comparison of measured and predicted values at Usk station are shown in figure 6. ➢ The largest watershed in BC, the Fraser, carries a predicted sediment load of 18143.7 10^6
kg/year (Milleman & Mease, 1987). In comparison, Hydrotrend predicts the mean annual sediment load for the Skeena to be 17145 10^6 kg/year.
➢ The model was better at capturing monthly trends in discharged when applied over the entire the Skeena watershed than over subbasins. When applied over the entire watershed,
Hydrotrend was generally able to capture the timing of monthly peaks and lows in discharge as observed in the measured values (figure 4). Timing was early for subbasins predictions. ➢ A comparison of the means z-test shows that the models mean predicted discharge over 360
months matches closely enough to the measured mean for the results to be considered
statistically equal. However, the model is underrepresenting the mean monthly discharge (by a average of 182𝑚3/s per month at Usk). Since the sediment load is dependent upon
discharge, the model is likely underestimating sediment load. With no measured sediment load data, the amount that the sediment load is being underrepresented cannot be verified.
➢ Although modelling the Skeena was possible, there were notable limitations. Limited data on groundwater storage and subsurface flow may have contributed to the model inaccuracy. A diverse area from coastal to interior may be contributing to model timing errors. Lack of measured data on sediment load and discharge at the river mouth has
made the model difficult to validate. Collecting sediment and discharge samples from the river mouth for validation and retrieving better groundwater estimates could improve the model. Annual changes in precipitation and temperature
varied throughout the watershed for the 1981-2010 normal making it difficult to predict long term changes.
Figure 5: Predicted Sediment and discharge amounts by Hydrotrend
Background: Beebe, 2008.
during peak discharge events (Bhangu and Whitfield, 1997). Changes in the amount, duration, and timing of discharge could
influence the influx of necessary nutrients into the Skeena Estuary. Alterations in the
proportions of fine sediments and gravels
deposited in association with discharge events can have an impact on spawning habitat for salmon (Gottesfeld & Rabnett, 2008).
➢ The Coast and Canyon Tsimshian, Gitxsan,
Wet’suwet’en, and Ned’u’ten reside, fish, and harvest within the watershed (Gottesfeld & Rabnett, 2008).
Figure 1: Sediment Plume at the Skeena Delta
Image from Google Earth 1997 Historic Imagery
Concluding Remarks
Figure 6: Comparison of Discharge up to USK Station
Figure 4: River Mouth Modelled Discharge trends compared to the Usk Station
Note on Figure 4: Natural trends in discharge at the delta will likely differ from the Usk measurements
(that the modelled delta predictions are being compared to) due a 12 052 km2 area contributing
to the river past Usk with a strong coastal influence. Mean delta discharge was estimated to be 1730 𝑚3/s by Hoos in 1975, which is 800m^3/s
more than the mean discharge at Usk.
➢ Future research using the model could be to model and compare multiple climate normal periods or to predict future discharge and
sediment load for the Skeena by utilizing predicted climate change scenarios over the watershed.
Amanda Wild, awild@uvic.ca
