Karl-Erich Lindenschmidt

Environmental risk of dissolved oxygen depletion of diverted flood waters in river polder systems - a quasi-2D flood modelling approach.

River polders are retention basins contained by levees alongside rivers into which water from the main river channel is diverted during extreme floods in order to cap the peak discharge of the flood hydrograph and to alleviate downstream flood risk by reducing the water levels. The retained water, however, is stagnant and the organic material in the water and the bottom sediments imposes a strong oxygen demand on the water. This paper presents a quasi two-dimensional computer-based methodology to assess the environmental risk exhibited by the operation of polders with which the concentration of dissolved oxygen in river and polder water can be simulated. A Monte-Carlo analysis allows the probability distribution of all the outcomes of the minimum dissolved oxygen levels in the water to be derived. From this analysis, the environmental risk of the dissolved oxygen concentrations in the polder water falling below 2 mg O2/L (the level considered critical for aquatic ecosystems) can be determined. The August 2002 extreme flood event on the Elbe River, Germany, with a proposed polder system variant was used to calibrate the model. A daily time step was used to for the simulations for a time frame 12-21 August 2008. The results show plausible spatial and temporal variations in the dissolved oxygen concentrations within the polders. The quasi-2D approach was successful in simulating the spatial distribution of water quality constituents in the polder system. There is up to approximately 20% risk that dissolved oxygen levels fall below 2 mg/L in the polders. This risk can potentially increase if sediment oxygen demand increases due to crop residue and water temperatures in polders increase. High nutrient transport in the river during flooding can cause a spurt of phytoplankton growth in the polders.

A quasi-2D flood modeling approach to simulate substance transport in polder systems for environment flood risk assessment.

In flood modeling, many one-dimensional (1D) hydrodynamic and water quality models are too restricted in capturing the spatial differentiation of processes within a polder or system of polders and two-dimensional (2D) models are too demanding in data requirements and computational resources, especially if Monte-Carlo techniques are to be used for model uncertainty analyses. The first goal of this paper is to show the successful development of a quasi-2D modeling approach which still calculates the dynamic wave in 1D but the discretisation of the computational units is in 2D, allowing a better spatial representation of the flow and substance transport processes in the polders without a large additional expenditure on data pre-processing and simulation processing. The models DYNHYD (1D hydrodynamics) and TOXI (sediment and micro-pollutant transport) were used as a basis for the hydrodynamic and water quality simulations. An extreme flood event on the Elbe River, Germany, with a proposed polder system variant was used as a test case. The results show a plausible differentiation of suspended sediment and zinc concentrations within the polders both spatially and temporally. This fulfills the second goal of this research. The third goal of this work is to provide an example methodology of carrying out an environmental risk assessment in inundated areas by flood waters, as required by the European Union floods directive. The deposition of zinc in polders was used for this example, due to its high contamination potential in the Elbe River. The extended quasi-2D modeling system incorporates a Monte-Carlo uncertainty analysis to assess the environmental impact of heavy metal deposition in the polders during extreme flooding. The environmental risk computed gives a 48% chance of exceeding the inspection value of 500 mg zinc/kg sediment for a flood such as the August 2002 event.

Physically-based hydrological modelling for non-point dissolved phosphorus transport in small and medium-sized river basins / Modélisation hydrologique à bases physiques et du transport de phosphore dissous diffus en bassins versants de petite et moyenne tailles

Abstract Abstract Current research suggests that strategies to control sediment and phosphorus loss from non-point sources should focus on different runoff components and their spatial and temporal variations within the river basin. This is a prerequisite for determining effective management measures for reducing diffuse source pollution. Therefore, non-point source models, especially in humid climatic regions, should consider variable hydrologically active source areas. These models should be able to consider runoff generation by saturated overland flow, as well as Hortonian overland flow. A combination of the hydrological model WaSiM-ETH and the erosion and P-transport model AGNPS was chosen for this study. The models were run in the WaSiM runoff generation mode (Green & Ampt/TOPMODEL or Richards equation approach) and the SCS curve number mode to assess the effect of these different runoff calculation procedures on the dissolved phosphorus yield. A small and a medium-sized river basin, of the area of 1.44 and 128.9 km2, respectively, in central Germany were selected for the investigation. The results show that the WaSiM–AGNPS coupling produces more accurate results than the SCS curve number method. For the spatial distribution, the more physically-based model approach computed a much more realistic distribution of water and phosphorus yield-producing areas.

Phosphorus input by nordic geese to the eutrophic Lake Arendsee, Germany

Phosphorus import by nordic geese (Anser fabalis and Anser albifrons) was investigated in Lake Arendsee, located in the Saxony-Anhalt region, Altmark, Germany during the period 1996 to 1997. Phosphorus contained in geese excrement on the ice was measured in the winters 1996 and 1997. In February 1996 (after 9 days of frozen lake surface) two excrement fields amounted to 80 ha and 30 ha in area and in January 1997, 10 days after ice closure, the excrement field was 106 ha large. The weight of excrement was estimated to be 148 to 266 g m -2 fresh weight (mean 201 g m -2 ) in 1996 and 83 g m -2 to 408 g m -2 (mean of 243 g m -2 ) in 1997. The average of phosphorus content was 8.5 mg g -1 dry weight in 1997 and 9.2 mg g -1 in 1996. Based on these values the phosphorus input attributed to nordic geese was calculated. Our results demonstrated a phosphorus import in 1996 after 9 days of frozen lake surface of 251 kg and in 1997 after 10 days of freezing of 173 kg. During 100 days of wintering, the nordic geese on Lake Arendsee produced a phosphorus load of 2.8 t in 1996 and 1.7 t in 1997. Compared with the annual phosphorus import from different sources, the contribution by nordic geese was 88 % in 1996 and 92 % in 1997. Its yearly phosphorus load during the winter months appears as a significant eutrophication factor for the trophic level of Lake Arendsee. However, the annual external load is approximately 10 % of the phosphorus poolsize in the lake water, and even less when considering the amount lodged in the bottom sediments.

A water coverage extraction approach to track inundation in the Saskatchewan River Delta, Canada

Tracking surface water coverage changes is a complicated task for many regions of the world. It is, however, essential to monitor the associated biological changes and bioproductivity. We present a methodology to track contemporary water coverage changes using optical remote sensing and use it to estimate historical summer water coverage in a large river delta. We used a geographical information system automated routine, based on the modified normalized difference water index, to extract the surface water coverage area (SWCA) from optical satellite data sets using the surface water extraction coverage area tool (SWECAT). It was applied to measure SWCA during drought and flood peaks in the Saskatchewan River Delta in Canada, from Landsat, SPOT and RapidEye images. Landsat results compared favourably with Canadian National Hydro Network (CNHN) GeoBase data, with deviations between SWCA classifications and the base CNHN GeoBase shapefile of ~2%. Difference levels between the extracted SWCA layer from Landsat and the higher resolution commercial satellites (SPOT and RapidEye) were also less than 2%. SWCA was tightly linked to discharge and level measurements from in-channel gauges (r2 > 0.70). Using the SWCA versus discharge relationship for the gauge with the longest record, we show that peak summer SWCA has declined by half over the last century, from 13% of our study area to 6%, with likely implications for fish and wildlife production.

Dynamic water quality modelling and uncertainty analysis of phytoplankton and nutrient cycles for the upper South Saskatchewan River

The surface water quality of the upper South Saskatchewan River was modelled using Water Quality Analysis Simulation Program (WASP) 7.52. Model calibration and validation were based on samples taken from four long-term water quality stations during the period 2007–2009. Parametric sensitivities in winter and summer were examined using root mean square error (RMSE) and relative entropy. The calibration and validation results show good agreement between model prediction and observed data. The two sensitivity methods confirmed pronounced parametric sensitivity to model state variables in summer compared to winter. Of the 24 parameters examined, dissolved oxygen (DO) and ammonia (NH3-N) are the most influenced variables in summer. Instream kinetic processes including nitrification, nutrient uptake by algae and algae respiration induce a higher sensitivity on DO in summer than in winter. Moreover, in summer, soluble reactive phosphorus (SRP) and chlorophyll-a (Chla) variables are more sensitive to algal processes (nutrient uptake and algae death). In winter however, there exists some degree of sensitivity of algal processes (algae respiration and nutrient uptake) to DO and NH3-N. Results of this study provide information on the state of the river water quality which impacts Lake Diefenbaker and the need for additional continuous monitoring in the river. The results of the sensitivity analysis also provide guidance on most sensitive parameters and kinetic processes that affect eutrophication for preliminary surface water quality modelling studies in cold regions.

Monitoring the Variation in Ice-Cover Characteristics of the Slave River, Canada Using RADARSAT-2 Data—A Case Study

The winter regime of river-ice covers in high northern latitude regions is often a determining factor in the management of water resources, conservation of aquatic ecosystems and preservation of traditional and cultural lifestyles of local peoples. As ground-based monitoring of river-ice regimes in high northern latitudes is expensive and restricted to a few locations due to limited accessibility to most places along rivers from shorelines, remote sensing techniques are a suitable approach for monitoring. This study developed a RADARSAT-2 based method to monitor the spatio-temporal variation of ice covers, as well as ice types during the freeze-up period, along the main channel of the Slave River Delta in the Northwest Territories of Canada. The spatio-temporal variation of ice covers along the river was analyzed using the backscatter-based coefficient of variation (CV) in the 2013–2014 and 2014–2015 winters. As a consequence of weather and flow conditions, the ice cover in the 2013–2014 winter had the higher variation than the 2014–2015 winter, particularly in the potential areas of flooded/cracked ice covers. The river sections near active channels (e.g., Middle Channel and Nagle Channel), Big Eddy, and Great Slave Lake also yielded higher intra-annual variation of ice cover characteristics during the winters. With the inclusion of backscatter and texture analysis from RADARSAT-2 data, four water and ice cover classes consisting of open water, thermal ice, juxtaposed ice, and consolidated ice, were discriminated in the images acquired between November and March in both the studied winters. In addition to river geomorphology and climatic conditions such as river width, sinuosity or air temperature, the fluctuation of water flows during the winter has a significant impact on the variation of ice cover as well as the formation of different ice types in the Slave River. The RADARSAT-2 based monitoring algorithm can also be applied to other river systems in high latitude ecosystems to annually monitor their river-ice variation and formation during the freeze-up and ice cover progression period.

The impact of macrophytes on winter flows along the Upper Qu’Appelle River

The Upper Qu’Appelle River conveys water from Lake Diefenbaker to Buffalo Pound Lake, which is a major source of water for domestic, industrial, agricultural and recreational use in southern Saskatchewan. Water demand continues to increase with time and additional conveyance capacity may be required during the winter months. Flows in the Upper Qu’Appelle are usually below 2 m3 s–1 from December to March; however, an increase in this flow rate will be needed to meet future water demands. A numerical modelling study was carried out to simulate the degree of ice cover thickening and backwater staging during freeze-up at various discharge scenarios (up to 6 m3 s–1). The Monte Carlo framework was used to capture the variability of possible parameter ranges within various freeze-up scenarios. A bottleneck to flow conveyance is a short 4-km stretch along the river (between the Prairie Farm Rehabilitation Administration [PFRA] and Tugaske Bridges) which is infested with macrophyte growth. Results show that the probability of overbank flow greatly increases with the presence of macrophytes in the channel, even at freeze-up conditions. Dredging was deemed the best mitigation option to reduce macrophyte density and remove nutrient-rich sediment to increase flow capacity.

Parameter Sensitivity of a Surface Water Quality Model of the Lower South Saskatchewan River—Comparison Between Ice-On and Ice-Off Periods

Little is known about seasonal differences (ice-on vs. ice-off periods) and the sensitivity of in-stream processes to surface water quality constituents in rivers that have a persistent ice cover in winter. The goal of this study is to investigate the sensitivity of nutrient transformation processes on surface water quality, especially rivers in cold regions where ice-covered conditions persist for a substantial part of the year. We established a sensitivity analysis framework for water quality modelling and monitoring of rivers in cold regions using the Water Quality Analysis Program WASP7. The lower South Saskatchewan River in the interior of western Canada, from the Gardiner Dam at Lake Diefenbaker to the confluence of the North and South Saskatchewan rivers, is used as a test case for this purpose. The study reveals that parameter sensitivities differ between ice-covered and ice-free periods and biological model parameters related to nutrient-phytoplankton dynamics can still be sensitive during the ice-covered season. For example, sediment oxygen demand is an important parameter during the ice-on period, whereas parameters related to nitrification are more sensitive in the ice-off period. These results provide insight into important water quality monitoring aspects in cold regions during different seasons.

The ecohydrological vulnerability of a large inland delta to changing regional streamflows and upstream irrigation expansion

Global Institute for Water Security, University of Saskatchewan, National Hydrology Research Centre, 11 Innovation Boulevard., Saskatoon, Saskatchewan S7N 3H5, Canada Department of Civil and Geological Engineering, University of Saskatchewan, 57 Campus Drive, Saskatoon, Saskatchewan S7N 5A9, Canada Department of Building, Civil and Environmental Engineering, Concordia University, 1455 de Maisonneuve Boulevard West, Montreal, Quebec H3G 1M8, Canada School of Environment and Sustainability, University of Saskatchewan, Kirk Hall, 117 Science Place, Saskatoon, Saskatchewan S7N 5C8, Canada Toxicology Centre, University of Saskatchewan, 44 Campus Drive, Saskatoon, Saskatchewan S7N 5B3, Canada Correspondence Elmira Hassanzadeh, Global Institute for Water Security, University of Saskatchewan, National Hydrology Research Centre, 11 Innovation Blvd., Saskatoon, SK S7N 3H5 Canada. Email: elmira.hassanzadeh@usask.ca