Investigation of Correlation between Remotely Sensed Impervious Surfaces and Chloride Concentrations

Water quality and nonpoint source (NPS) pollution are important issues in many areas of the world, including the Greater Toronto Area where urban development is changing formerly rural watersheds into impervious surfaces. Impervious surfaces (i.e. roads, sidewalks, parking lots, strip malls, building rooftops, etc.) made out of impenetrable materials directly impact hydrological attributes of a watershed. Therefore, understanding the degree and spatial distribution of impervious surfaces in a watershed is an important component of overall watershed management. According to Environment Canada’s estimates, road salts, also considered nonpoint source pollutants, represent the largest chemical loading to Canadian surface waters. The main objective of this study is to verify the often assumed correlation between impervious surfaces and chlorides that result from the application of road salts, focusing on a case study in the selected six major watersheds within the Greater Toronto Area. In this study, Landsat-5 TM images from 1990, 1995, 2000, and 2005 were used in mapping urban impervious surface changes within the study area. Pixel-based unsupervised classification technique was utilized in estimation of percentage impervious surface coverage for each watershed. Chloride concentrations collected at Water Quality Monitoring Stations within the watersheds were then mapped against impervious surface estimates and their spatiotemporal distribution was assessed. In a GIS environment, remotely sensed impervious surface maps and chloride maps were overlaid for the investigation of their potential correlation. The main findings of this research demonstrate an average of 12.9% increase in impervious surface areas as well as a three-fold increase in chloride concentrations between 1990 and 2005. Water quality monitoring stations exhibiting the highest amounts of chloride concentrations correspond with the most impervious parts of the watersheds. The results also show a correlation (coefficient of determination of 0.82) between impervious surfaces and chloride concentrations. The findings demonstrate that the increase in imperviousness do generate higher chloride concentrations. Correspondingly, the higher levels of chloride can potentially degrade quality of surface waters in the region. Through an innovative integrated remote sensing approach, the study was successful in identifying areas most vulnerable to surface water quality degradation by road salts

A Multi-Scale Approach in Mapping the Sedimentological and Hydrostratigraphical Features of Complex Aquifers

Accessibility to consistent subsurface hydrostratigraphic information is crucial for the development of robust groundwater flow and contaminant transport models. However, full three-dimensional understanding of the subsurface geology is often the missing link. Construction of watershed-scale hydrostratigraphic models continues to be limited by the quality and density of borehole data which often lack detailed geologic information. This can become a serious problem where rapid sediment facies changes and intricate sediment architecture occur. This research is motivated by the idea that if we can understand more about the distribution of sediments and structures of complex deposits, we learn more about depositional processes and how they affect the internal geometry of a deposit and the distribution of hydraulic properties. One approach is to study surficial excavations (e.g. sand and gravel pits) that often punctuate shallow aquifers. The purpose of this study is to develop and test a method of integrating high-resolution georeferenced stratigraphic and sedimentologic information from sand and gravel pits as a means to better document sedimentologic data and improve understanding of the depositional environments. The study area is located within the Waterloo Moraine, in southwestern Ontario, and is an unconsolidated shallow aquifer system with a complex internal architecture and sediment heterogeneity. The method involves the integration of high-resolution field data with borehole and geophysical information in a computer-based 3D environment. A total of fourteen virtual sedimentary sections were constructed by georegistering digital photographs within a framework of georeferenced positions collected using a reflectorless total station and GPS. Fourteen sediment facies have been described in the field. These include crudely stratified gravel beds, planar and cross-laminated sandy strata (ripple and dune scales), along with laminated and massive silty and clayey beds. Calculated hydraulic conductivities span over seven orders of magnitude. The analysis of a single excavation has shown contrasting sediment assemblages from one end of the pit to the other, highlighting the complexity of the Waterloo Moraine. The heterogeneous and deformed layers of gravel, sand, and mud may be the product of an ice-contact to ice-proximal environment, whereas the extensive sandy assemblages may reflect an intermediate subaqueous fan region. The results also suggest that the borehole database overestimates the amount of fine-grained material in the study area. Finally, this research demonstrates that it is possible to build in a timely manner a 3D virtual sedimentologic database. New emerging technologies will lead to increased resolution and accuracy, and will help streamline the process even further. The possibility of expanding the 3D geodatabase to other excavations across the region in a timely manner is likely to lead to improved hydrostratigraphic models and, by extension, to more efficient strategies in water resources planning, management and protection

Deriving Spatial Patterns of Severe Rainfall in Southern Ontario

Severe weather is a natural product of the earth’s atmosphere. Water delivered by storms sustains important biophysical functions whereas from a human perspective severe weather can have negative effects when damage is caused to material assets and health. Modern society has acquired knowledge and technological know-how to deal with the effects of severe weather on human activity. In Canada storm water management infrastructure and land management practices reflect decades of analysis of weather data. In Ontario the engineering of storm water management infrastructure has assumed a long term climate ‘normal’ to guide specifications for safely operating during severe storm events. Water resource managers also consider long term climate records to guide decision-making for water use and allocation. However, given the measured and predicted effects of global warming, climate normals generated from data from the past may not be suitable for planning for the climate of the future. From the Fourth Assessment by the Intergovernmental Panel on Climate Change it is generally accepted that one of the predicted effects of climate change will be shifts in the intensity, the frequency and the spatial distribution of severe storm events. Human activity in regions affected by these changes will be required to make adjustments to their water and land management practices and to make better strategic decisions about the use of existing knowledge and technology to adapt to change. The climate in Southern Ontario is expected to shift to earlier snow melt, earlier spring storms and increased storm severity throughout the summer season. The region is particularly vulnerable to the combined effects of these climate parameters in the spring months of March, April and May when the risk of flooding and erosion is at its greatest. The predicted increase in summer rainfall intensity will have negative impacts for soil erosion and flood damage. This paper presents an analysis of 46 years of climate data in Southern Ontario. The spatial distribution of intense rainfall is examined to determine the extent to which rainfall exhibits localized patterns and whether there have been changes in the patterns over the period of data. The spatial patterns of severe rainfall between the months of March and September are also examined with the use of 13 years of radar data. A comparison of one hour rainfall measured from NEXRAD radar data to Environment Canada’s intensity duration frequency (IDF) data demonstrates a technique of spatial analysis that could aid in revising IDF values and indentifying areas that experience a higher frequency of intense rainfall events

The geology and hydrogeology of buried bedrock valley aquifers on Cape Breton Island, Nova Scotia: an overview

Buried bedrock valley aquifers are common across Canada, where multiple glaciations have buried both pre-glacial and Pleistocene valleys. These aquifers are becoming increasingly important as a supply of potable groundwater, for supporting aquatic habitat, and as part of strategies in adapting to a changing climate. However, in Canada, there are considerable knowledge gaps at national, regional, and local scales, such that many buried bedrock valleys remain unidentified or underexplored. Cape Breton Island provides a hydrogeological view into the roots of an ancient mountain range, now exhumed, glaciated, deglaciated, and tectonically inactive. Since the Cretaceous, a variety of geological processes have formed several buried bedrock valley aquifers over the island. These aquifers are important in providing municipal and commercial groundwater supplies, controlling mine dewatering, protection of salmonids, design and monitoring of waste disposal sites, and geotechnical investigations for infrastructure design. Of 150 sites assessed, 61% provided evidence of buried aquifers comprising unconsolidated sand and gravel of Cretaceous, Pleistocene, and Holocene ages. These sites provided the basis for five conceptual, 3-D hydrogeological block models. Three hydrogeological case studies provided further insight into the functioning of two of these models. Future studies should identify and characterize aquifers in high demand areas and/or those that support important riverine ecosystems. Research should focus on aquifer properties, groundwater-stream interaction, and the impact of changing climate with sea-level rise

Flow pathways and nutrient transport mechanisms drive hydrochemical sensitivity to climate change across catchments with different geology and topography

Hydrological processes determine the transport of nutrients and passage of diffuse pollution. Consequently, catchments are likely to exhibit individual hydrochemical responses (sensitivities) to climate change, which are expected to alter the timing and amount of runoff, and to impact in-stream water quality. In developing robust catchment management strategies and quantifying plausible future hydrochemical conditions it is therefore equally important to consider the potential for spatial variability in, and causal factors of, catchment sensitivity, as it is to explore future changes in climatic pressures. This study seeks to identify those factors which influence hydrochemical sensitivity to climate change. A perturbed physics ensemble (PPE), derived from a series of global climate model (GCM) variants with specific climate sensitivities was used to project future climate change and uncertainty. Using the INtegrated CAtchment model of Phosphorus dynamics (INCA-P), we quantified potential hydrochemical responses in four neighbouring catchments (with similar land use but varying topographic and geological characteristics) in southern Ontario, Canada. Responses were assessed by comparing a 30 year baseline (1968-1997) to two future periods: 2020-2049 and 2060-2089. Although projected climate change and uncertainties were similar across these catchments, hydrochemical responses (sensitivities) were highly varied. Sensitivity was governed by quaternary geology (influencing flow pathways) and nutrient transport mechanisms. Clay-rich catchments were most sensitive, with total phosphorus (TP) being rapidly transported to rivers via overland flow. In these catchments large annual reductions in TP loads were projected. Sensitivity in the other two catchments, dominated by sandy loams, was lower due to a larger proportion of soil matrix flow, longer soil water residence times and seasonal variability in soil-P saturation. Here smaller changes in TP loads, predominantly increases, were projected. These results suggest that the clay content of soils could be a good indicator of the sensitivity of catchments to climatic input, and reinforces calls for catchment-specific management plans

Towards a Management Plan for the Waterloo Moraine: A Comprehensive Assessment of its Current State within the Region of Waterloo

The Region of Waterloo (ROW) and Oxford County contain a significant landscape unit called the Waterloo Moraine that provides multiple ecological and water resource functions to surrounding communities. These functions include; providing a clean and abundant source of water, natural landscapes for plant and animal habitats, natural areas for recreational enjoyment, prime agricultural lands on which to grow food and aggregate resources in close proximity to large markets. This landscape unit is similar to the Oak Ridges Moraine (ORM) located in the Greater Toronto Area (GTA). The purpose of this research is to conduct an examination of the current state of management for the Waterloo Moraine within the ROW and Oxford County. Attributes of the Waterloo Moraine examined include; water resources, agricultural resources, mineral aggregate resources, Environmentally Sensitive Landscapes (ESLs), natural core areas, natural linkage areas and settlement areas. While the hydrologic functions have been most studied within this landscape unit, the Moraine has predominantly been studied from a focused perspective rather than a comprehensive one. Using expert knowledge and available secondary sources the following research questions are investigated: (1) What do we currently know about the Waterloo Moraine and how is this knowledge (or lack thereof) applied to its future existence and sustainability? (2) Who are the stakeholders when it comes to growth and management of the Waterloo Moraine? (3) Which places need to be protected from development most throughout the Waterloo Moraine? (4) Where does the Waterloo Moraine fit into management policies and plans existing in the Region of Waterloo and within the Province of Ontario? Key results of this research include; (1) The boundary of the Waterloo Moraine remains undefined; however, rough estimates of the overall size and various portions within each county, township and city it encompasses have been projected. To date, the largest portion of the Moraine lies in Wilmot Township (36.9%) and the smallest portion lies in North Dumfries (3%). (2) Many stakeholders are involved in the protection and management of the Waterloo Moraine. Regional and provincial officials ultimately control where development and growth occur and which areas in the ROW should be protected most. Those responsible for the initial ‘push’ for Moraine protection are grassroots groups and individuals coupled with the local media. (3) Criteria designating development ‘hot spots’ across the Waterloo Moraine has been established and six ‘hot spots’ within the Waterloo Moraine are designated. Limited recognition has been given to the Waterloo Moraine complex in regional policies. It is therefore suggested that the creation of a Waterloo Moraine Act be considered in order to protect and manage this landscape unit. The Act would promote protection measures for the Moraine’s valuable attributes at the highest provincial level and eventually lead to a conservation plan. It is recommended that the ROW further refine the Waterloo Moraine’s boundaries, develop a database to monitor changes in various features and functions across the Waterloo Moraine’s landscape and promote the implementation of a Waterloo Moraine Act

The influences of spatially variable rainfall and localized infiltration on groundwater recharge in a water management context

Water management involves monitoring, predicting, and stewarding the quality and quantity of groundwater recharge at the watershed scale. Recharge sustains baseflow to streams and replenishes water extracted by pumping at wells; it is frequently estimated using numerical models that couple or fully integrate surface water and groundwater domains and use water budgets to partition water into various components of the hydrological cycle. However, uncertainty associated with the input data for large components such as precipitation and evapotranspiration may hinder model accuracy, and preferential flow dynamics such as depression focused recharge (DFR) may not be represented at typical modelling scales (≥10s of sq. km) or with typical approaches. The present study addressed two themes related to groundwater sustainability and vulnerability: 1) the sensitivity of modelled recharge estimates to the spatial variability of rainfall, and 2) the vulnerability of public supply wells to DFR during large-magnitude rainfall or snowmelt events. The region investigated during this research was the Alder Creek watershed (78 sq. km), a typical southern Ontario setting overlying glacial moraine sediments with mostly agricultural land use, some urban and aggregate resource development, and whose recharge supplies multiple municipal well fields for the cities of Kitchener and Waterloo. Rainfall is often the largest component of the water budget and even a small uncertainty percentage may lead to challenges for accurately estimating groundwater recharge as a calculated residual within a water budget approach. However, rainfall monitoring networks typically have widely spaced gauges that are frequently outside the watershed of interest. Assessment of the influence of spatially variable rainfall on annual recharge rate estimates was performed by comparing transient simulations using input data from three different rain gauge networks within a coupled and fully-distributed numerical model. A local network of six weather stations with rain gauges was installed and operated in and around the study watershed for three years, and data from six regional stations (within 30 km of the watershed) and one national station (3 km from the watershed) were obtained from publicly available sources. Time series of distributed, daily rainfall were interpolated via the inverse distance squared method using data from each of the rain gauge networks for three calendar years. The temporal and spatial snowfall distribution was consistent among all scenarios, to maintain focus on differences caused by the rainfall input data. Results showed that annual average recharge rates could differ considerably between scenarios, with differences sometimes greater than the water-budget derived uncertainty for recharge. Differences in overall recharge between pairs of scenarios involving the local rain gauge network were largest, varying by up to 141 mm per year, or 44% of the steady state recharge estimated in a previous study. Streamflow estimates for the local rainfall simulations were closer to observations than those using regional or national rainfall. Because the three scenarios used the same set of underlying soil parameters, the results suggest that the availability of local rainfall measurements has the potential to improve the calibration of transient watershed hydrogeological models. The second theme of the present study was exemplified by the Walkerton tragedy in 2000, where pathogenic microbes were rapidly transported from ground surface to a public supply well during a heavy rainfall event. The vulnerability of such wells to surface-originating contaminants during major hydrological events remains poorly understood and is difficult to quantify. Such events may result in overland flow collecting in low topographic locations, leading to localized infiltration. If focused recharge occurs in the immediate vicinity of a public supply well, the threat to the water quality of that well may significantly increase temporarily. These conditions are frequently encountered within the glaciated landscape of southern Ontario. Conventional approaches for defining the threat of groundwater under the direct influence of surface water (GUDI) do not routinely account for this type of transient infiltration event and instead assume steady state flow fields without localized recharge. The present study combined the monitoring and modelling of a site in southern Ontario where DFR is routinely observed to occur within 50 m of a public supply well. Extensive site characterization and hydrologic monitoring were conducted at the site over a period of 3.5 years, specifically during large-magnitude hydrologic events including heavy rainfall and snowmelt. Integrated surface water – groundwater models employing HydroGeoSphere (HGS) were used to quantify the transport of potential contaminants infiltrating beneath a depression and a creek and the associated risk to the public supply well. Simulated relative concentrations at the well were below “detection” for typical median contaminant concentrations in surface water but > 1 cfu/100 mL with travel times between 118 and 142 days for creek and DFR solutes, respectively, based on maximum initial surface water concentrations. Results suggest that DFR and localized recharge could increase the threat to overburden wells under extreme conditions. Ponding reduced travel time by at least 58 days for the DFR solute. In order to extend the analysis of recharge estimate sensitivity to spatial rainfall variability to the longer term, and to incorporate the influence of actual evapotranspiration (AET) uncertainty, a method was developed to employ stochastic rainfall time series and AET estimates in a Monte Carlo framework to quantify the resulting variability in recharge estimates and three groundwater management metrics. Stochastic rainfall time series were generated via a parametric, mixed exponential method for three virtual stations within the Alder Creek watershed and constrained by field-derived spatial correlation coefficients. Observed snowfall data from one nearby national weather station were used to calculate total precipitation. Stochastic annual AET estimates were generated based on: 1) calculated annual potential evapotranspiration at the national weather station, 2) observed variation about the Budyko curve in 45 US MOPEX watersheds with PET/P ratios within ±0.05 of the average ratio calculated for the national weather station near the watershed, and 3) a correction factor to remove AET from the saturated zone. Recharge rates for the Alder Creek watershed were calculated via a 46-year vadose zone water budget for each of 16,778 realizations. The surface water fraction of streamflow was estimated using hydrograph separation results for the watershed. It was hypothesized that spatially variable precipitation would exert more influence on recharge than AET because it is a larger component of the local water budget. Groundwater recharge results were applied to three different metrics related to water quality, well vulnerability, and water quantity. Results suggest that estimates of non-point source contaminant loadings to the water table could differ by up to ±14% from the average. Worst case changes in capture zone area estimates for a public supply well could be up to ±15% different from the average. The ratio of maximum to minimum cumulative recharge over all realizations was 1.31, though contributions from spatial rainfall variability alone led to a ratio of 1.15. This suggests that AET uncertainty and spatial rainfall variability each contribute nearly the same amount of variability to recharge estimates. This latter ratio is less than the result (~2) from a previous study of a much larger watershed in Spain. The results highlight the importance of AET estimates for recharge rate estimation, and their potential impacts on land use planning and groundwater management. This method could be used to project impacts of climate change on recharge variability at the watershed scale. Overall, results suggest that the spatial variability of rainfall could impact recharge rate estimates in numerical models of small to medium sized watersheds (e.g., 78 sq. km), especially during short simulations. Annual recharge estimates could vary over a range equivalent to 44% of a previously estimated steady state value, though long-term (46-yr) estimates could vary over a range equivalent to 12% of this value due to averaging over time. Non-point source loadings and capture zone areas could vary up to ±7.0% and ±7.4% from the average, respectively, over the long term due to spatial rainfall variability, though uncertainties associated with AET could increase this to ±14% or ±15%, respectively. The hydrological event characterization and well vulnerability modelling of the second research theme suggest that localized recharge could lead to increased microbial risks for wells screened in overburden sediments during large hydrological events (≥ 40 mm rainfall over 4 days) through the phenomenon of temporary ponding. The method developed for the long-term stochastic recharge rate analysis could be applied in other settings as an alternative to, or to complement, large-scale, fully-distributed 3D numerical modelling