Controls of Groundwater Floodwave Propagation in Gravelly Floodplain

Journal Article Summary 

 

In their journal article titled “Controls of Groundwater Floodwave Propagation in Gravelly Floodplain, Cloutier et al. (2014) are interested in the relationship between the surface water and groundwater in the floodplain of the Matane River, which is located in eastern Canada and which drains a 1678 square kilometer basin. As described in the article, the mean annual discharge of the stream, collected from the Matane gauging station, is 39 m³ per second, with the highest discharge in May. In the research study, the author proposed two feasible scenarios of driving mechanisms of the rise of groundwater which ultimately causes flood to occur, and these two scenarios are: (1) complete saturation of subsurface strata due to precipitation over a long period of time and (2) river stage fluctuation. Each scenario was analyzed, and the result showed that river stage fluctuation had stronger effect on the rising of groundwater level. 

For data collection, eleven piezometers were installed at the study site for 173 days in the summer and fall of 2011 (from 21 June to 12 December 2011) in order to examine the hydraulic heads of the floodplain, the ground water flows, and stream outflows where there is an occurrence of groundwater exfiltration. The authors also mention that there are evidences of the success of using the arrays of piezometers for documenting the interactions between surface water and groundwater.  For the first 79 days, from 21 June to 7 September, eight of the eleven piezometers were used accompanied by transducers (Hobo U20-001) to automatically record the water level at every 15 minutes. Then, starting from September 7 onwards, three more pressure transducers were added to the rest of piezometers, D139, D21, and D 196 (Cloutier et al., 2014). At upstream and downstream of the experimental site, two river stage gauges were installed on the river bed with an intent to monitor water levels in the river at every 15 minutes for the whole of the study period.  Magellan ProMak III differential GPS was used to measure the locations of piezometers, a LIDAR survey to obtain a topographic map, and a tipping bucket pluviometer to measure the rainfall data (Cloutier et al., 2014).

At the piezometer stations and river station gauge upstream (RSGup), the water levels and river stages were higher than those of stations, and hence there is no problem with time series dat. However, at the river station gauge downstream (RCGdn), the rivers stages occasionally dropped below the data logger, resulting in discontinuous time series. To deal with this, the authors decided to use the RSGdn time series only from 5 to 12 September. Alternatively, cross-correlation analyses, performed with the PAST software, were adopted to determine the time lags between time series of the river stages and the water level at the piezometers (Cloutier et al., 2014). In addition, this method was also used to obtain the information concerning the strength of the input-output relationships as well as the time lags between the processes. Owing to the small distance between the two river gauges, no significant lag between RSGup and RSGdn was account for.

The results from the study show that the relationships between the water level in the river and ground water is much stronger than that between precipitation and groundwater due to the fact that the input from precipitation has been hugely reduced by the unsaturated zone which are able to store a large amount of water. It is also interpreted that the amplitude of groundwater fluctuation is disproportional to the distance from the river (Cloutier et al. 2014), meaning that the further the distance from the river, the lower the amplitude of the groundwater fluctuations. In addition, the result also suggests that “fluctuations of hydraulic head correspond to the propagation of groundwater floodwave throughout the floodplain” (Cloutier et al., 2014).

The aforementioned research study, I believe, is essential for later study about surface water-groundwater interaction, especially in the state of Florida where ground water is known to be the indispensable source of drinking water and other usage, and in which there is a strong connection between surface water and groundwater. According to Florida Department of Environmental Protection (2013), in the state of Florida, 90 percent of its population depends on groundwater for drinking water. In their article, Winter et al. (1998) wrote that almost all, if not all, of surface-water features such as streams, lakes, reservoirs, wetlands, estuaries, and the like has interactions with underground water, and often times surface-water bodies gain water from the groundwater and vice versa, which implies that they are closely related to each other and if one is polluted or affected, the other will also be affected. Therefore, I think that the study by Clotier et al. (2014) is useful and can be used as a case study in Florida where a strong connection between surface and groundwater is present. More importantly, understanding the surface water-groundwater interaction helps water engineers, hydraulic engineers, water resource managers, as well as other stakeholders in water-related policy forming effectively manage the local water resource and protect the water resource. 

References

Cloutier, A. C., Bélanger, B. T, and Larocque, M. (2014). “Controls of groundwater floodwave propagation in a gravelly floodplain.” Journal of hydrology. 511(2014) 423-431. Retrieved on 03/16/2014 from http://www.sciencedirect.com/science/article/pii/S0022169414001115

Florida Department of Environmental Protection (2014). Retrieved on 03/16/2014 from http://www.dep.state.fl.us/water/groundwater/whatis.htm

Winter, C. T., Harvey. W. J., Franke, L. O., and Alley, William, M. W. (1998). Groundwater and surface Water A Single Resource. U.S. Geological Survey Circular 1139. Denver, Colorado. Retrieved on 03/16/2014 from http://pubs.usgs.gov/circ/circ1139/pdf/circ1139.pdf