HR: 0800h
AN: H31D-1326    [Abstracts]
TI: Selecting a calculation method to estimate sediment and nutrient loads in streams: application to the Beaurivage River (Quebec, Canada)
AU: * Rousseau, A N
EM: alain_rousseau@ete.inrs.ca
AF: Institut National de la Recherche Scientifique, Centre Eau, Terre et Environnement, 490 rue de la Couronne, Quebec, QC G1K9A9 Canada
AU: Quilbé, R
EM: renaud_quilbe@ete.inrs.ca
AF: Institut National de la Recherche Scientifique, Centre Eau, Terre et Environnement, 490 rue de la Couronne, Quebec, QC G1K9A9 Canada
AB: Estimation of sediment and contaminant loads is based on streamflow and concentration data. In general, stream gauges continuously monitor streamflow, while contaminant concentrations are measured less frequently because of high costs of sampling and laboratory analyses. The classical question is: how to accurately estimate seasonal or annual loads when the only available concentration data are from a weekly or even monthly sampling? To do so, different calculation approaches have been developed over the last decades. The classical approaches are deterministic: averaging methods, ratio estimators, regression methods (rating curves) and planning level load estimation methods. This presentation proposes a rapid overview of these methods as well as a framework to select the most suited with respect to available data. First, correlations between contaminant concentration and streamflow should be checked. If correlations are strong enough, regression methods should be used in priority. Otherwise, averaging methods or ratio estimators are more appropriate. In a case study involving a six-year data set (1989 to 1995) from the Beaurivage River (Quebec, Canada), we used the ratio estimator to estimate annual and seasonal loads of sediments and nutrients (N and P). Results show relatively steady annual loads (on average 8.1 kg.ha.yr-1 and 1.1 kg.ha.yr-1 for total dissolved N and total P respectively) and a low erosion rate (0.23 t.ha.yr-1). The results also confirm that nutrient and sediment transport via runoff is essentially a springtime process in this region, and they indicate that dissolved P represents the bulk of the total P load, most likely due to artificial subsurface drainage systems in the watershed. These results are compared to loads obtained with other averaging methods and with data from literature, confirming the order of magnitude but highlighting the large uncertainties that remain with such deterministic methods. Finally, some research avenues are proposed to investigate other estimation methods adapted to data characteristics, for instance by combining a regression method for high flow conditions and an averaging method for low flow conditions, or by giving different weights to measured and estimated concentration values in load calculation. Statistical methods may also help to better take into account and quantify uncertainty.
DE: 1815 Erosion
DE: 1862 Sediment transport (4558)
DE: 1871 Surface water quality
DE: 1879 Watershed
SC: Hydrology [H]
MN: Fall Meeting 2005