Dec 21, 2014

Impacts of the freshet on ice cover breakup and resulting flood risk implications along the Upper Qu’Appelle River SK, Canada

During the ice breakup period in the Upper Qu’Appelle River (QAR), higher flows from the freshet can lead to ice jamming, overtopping of channel dykes and bridge decks and flooding of surrounding agricultural areas along the river The Qu’Appelle River dam regulates the flow from the Lake Diefenbaker to the downstream upper Qu’Appelle River (Figure-1). At the end of the winter season, ice thicknesses begin to reduce due to increased air temperatures and river water temperatures. Despite of drastic reductions in discharge prior to freshet runoff, mechanical ice breakup and jamming may still occur, depending on the amount of snow remaining in the basin, the strength competency of the ice cover and the rate at which air temperatures increase. Previous studies provide an indication of the severity of ice jamming and flooding that could occur at the most vulnerable section of the Upper Qu’Appelle River, between the PFRA Bridge and Tugaske Bridge bridges (Figure-3), where dyke crests and bridge decks are lowest in elevation relative to the channel.
Figure 1: The Qu'Appelle River
The Upper QAR is the initial part of the Qu’Appelle River basin. This river basin initiates from the Qu’Appelle River dam on the Gordon McKenzie arm of Lake Diefenbaker and drains into the Assiniboine River in the Saskatchewan- Manitoba border. The Upper QAR is stretched upto Lumsden where Wascana Creek joins the Qu’Appelle River. The portion of the upper QAR from the Qu’Appelle River Dam to just upstream of the Eyebrow Lake near Tugaske Bridge is the study area.

The QAR watershed is located in the southern part of Saskatchewan. Its basin area is 74,589 km2, where 93% area is agricultural land. Total population is 328,365. Two major cities are located here, namely Regina and Moose Jaw. Five potash mines are located in this watershed. A study reveals that the future water demand (for 2020, 2040 and 2060) in the watershed is projected to be increased by 12%, 30% and 39% of the water demand of 2010 (Kulshreshtha, Nagy, & Ana, 2012).

Figure 2: Digital Elevation Model (DEM) of study area
The study of the local DEM guides the study area selection. Local DEM (available from GeoBase with 10 m resolution) shows that the portion of the river from dam to just upstream of the Eyebrow Lake has a flatter bank. This flat riverbank is prone to flood water overtopping, which makes it vulnerable to ice jam flood. In addition, this portion of river contains four bridge. Bridge piers are the possible location for ice jamming and subsequent flood event (Lindenschmidt, 2014).

Figure 3: River alignment and location of bridges
Ice cover breakup normally occurs due to temperature rise and increase of river flow. Temperature shows increasing trend in the month of April. This phenomenon leads to ice cover breakup. Temperature rise also expedite the overland freshet runoff into the river, which accumulates with in-channel freshet. This sudden increment leads to hinge crack of ice cover. Hinge crack initiates traverse crack. In case of high flow in the river, broken pieces of ice often leads to ice jam in the river and create a sudden intense flood in the vicinity. In spite of temperature rise and snow melting in the watershed, in some part of Canada experience unseasonal warm weather and moderate amount of rainfall in the month of late January- early February (New Brunswick River Ice Manual, 2011). This phenomenon often leads to premature breakups in the ice cover leading to ice jamming in the river.

Figure 4: Observed River flow in the Qu'Appelle River Dam drop structure
The Qu’Appelle River dam controls the downstream river. In the early January, dam authority brings the flow down to 0.8 m3/s to avoid any premature crack in the ice cover. The purpose of this control is to create the scope to thaw the ice cover and avoid winter ice jam flooding. From late March to early April, air temperature shows a rising trend. In mid to late April, temperature is high enough to melt down the ice cover. In this time, authority almost shut off the river flow (0.1 m3/s), because river flow in addition with freshet from overland snow can create unwanted ice jam and subsequent flooding. Dam authority brings the river flow to normal by mid to late May, when air temperature stabilize. In year 2013, air temperature in 27 April shows a 15o C rise (Figure-4). In that date, dam authority almost shut off the river flow. River flow was bring back to normal (4 m3/s) in late May. Figure-5 shows 2013 water level at Tugaske Bridge, which is situated 13.5 km downstream of the drop structure. In 27 April, water level shows a downward trend. This is an indication of coming flood surge. The water level of the ice cover becomes low in front of water surge, and it may create an imminent ice jam. Water level rise 0.8 m in the afternoon of 27 April near Tugaske Bridge and water level fluctuates for next 2 days, which indicates ice jamming and releasing. From 30th April afternoon, water level stabilize to 527.2 m.

Figure 5: Water elevation profile at Tugaske Bridge
Figure 6: The Qu'Appelle River system linkage among different processes
The upper Qu’Appelle River (QAR) system contains the linkage among other hydrological and anthropogenic processes. River flow, ice breaking, river morphology, ice jam flooding, macrophytes development dependent of local hydrology i.e. precipitation, evapotranspiration, snowmelt etc., hydrologic transport process i.e. erosion, shear velocity etc. and human activities i.e. landuse practice, industrialization, Qu’Appelle dam operation etc.

Precipitation, evapotranspiration, snowmelt, wind blow etc. affects overland runoff and surface erosion. For the Qu’Appelle River system, the amount of freshet is very important for ice breaking and flooding, because dam authority shut off the flow from Lake Diefenbaker during the month of April. Eroded soil deteriorate water quality. Human induced pollution also affect river water quality i.e. TDS, total phosphorus, DOC etc.

During the month of April (when temperature rises and river and surface ice begin to melt), river flow in the upper QAR increase and the chance of ice jamming increase. This causes high shear velocity, hanging dam and riverbed scouring. It increases the suspended sediment in water, and change the river morphology i.e. sinuosity, slope. During the time of ice jam flood, a sudden blockade occurs in the course of river, which may cause river water to intrude adjacent land surface at a fast pace. This phenomenon disrupts fish habitat. Moreover, it damages riverbank properties i.e. agricultural land, human settlements.

The QAR has a substantial economic effect as many human activities has grown on the bank of this river. A certain amount of water is required for downstream water demand, environmental flow, recreation etc. Due to climate change situation, water supply is tend to reduce and water demand is tend to increase in the watershed (Kulshreshtha et al., 2012). Therefore, it is important to study the safe margin of water bearing capacity during the critical time to satisfy the downstream water demand and minimize the chances and magnitude of ice jam flood.


Reference
Beltaos, S. (2012). Distributed function analysis of ice jam flood frequency. Cold Regions Science and Technology, 71, 1–10. doi:10.1016/j.coldregions.2011.10.011
Kulshreshtha, S., Nagy, C., & Ana, B. (2012). Present and Future Water Demand in the Qu’Appelle River Basin. Saskatoon. Retrieved from https://www.wsask.ca/Global/Lakes and Rivers/Provincial Forecast/2014/QuAppelle Water Demand Study.pdf
Lindenschmidt, K.-E. (2012). Ice Jam Modelling of the Lower Red River. Journal of Water Resource and Protection, 04(01), 1–11. doi:10.4236/jwarp.2012.41001
Lindenschmidt, K.-E. (2014). Winter Flow Testing of the Upper Qu’Appelle River. LAP LAMBERT Academic Publishing (pp. 11–12). doi:978-3-659-53427-0
New Brunswick River Ice Manual. (2011). Fredericton NB: Communication New-Brunswick. Retrieved from http://webcache.googleusercontent.com/search?q=cache:Z2WtB_UEDVYJ:www2.gnb.ca/content/dam/gnb/Departments/env/pdf/Publications/RiverIceManual.pdf+&cd=1&hl=en&ct=clnk&gl=ca