Daniel L. Peters

Runoff Production in a Forested, Shallow Soil, Canadian Shield Basin

Storm flow in forested basins on the Canadian Shield is largely supplied by subsurface water; however, mechanisms by which this water reaches the stream remain unclear. Side slope contributions to storm flow were studied using throughflow trenches on slopes in a headwater basin near Dorset, Ontario. Discharge, soil water content, and chemical and isotopic signatures of subsurface water were monitored at each site. Four hypotheses were tested: (1) most flow occurs at the soil-bedrock interface on shield slopes with thin soil; (2) a significant fraction of event water moves vertically to bedrock via preferential flow pathways and laterally over the bedrock surface; (3) relative preevent water contribution to subsurface flow on shield slopes is a function of soil thickness; and (4) a significant portion of event water flux in storm flow from forested basins with shallow soil cover is supplied from side slopes via subsurface flow along the soil-bedrock interface. Hypothesis 1 was confirmed from hydrometric observations during spring and fall rainstorms. Hypotheses 2 and 3 were supported by temporal trends in dissolved organic carbon and 18O in flow at the soil-bedrock interface and by isotopic hydrograph separations (IHSs) of hillslope runoff. Comparison with the streamflow IHS indicated that event water flux from the basin in excess of that attributable to direct precipitation onto near-channel saturated areas could be supplied by flow along the bedrock surface (hypothesis 4). Flow at the soil-bedrock interface on side slopes also contributed ∼25% of preevent water flux from the basin. Much of the event water component of basin storm flow may travel considerable distances via subsurface routes and is not necessarily contributed by surface runoff processes (Horton flow or saturation overland flow). Therefore the assumption that event water undergoes little interaction with the soil during its passage downslope may be unwarranted here.

INFERRING HYDROLOGICAL PROCESSES IN A TEMPERATE BASIN USING ISOTOPIC AND GEOCHEMICAL HYDROGRAPH SEPARATION: A RE‐EVALUATION

Simultaneous monitoring of conservative and non-conservative tracers in streamflow offers a valuable means of obtaining information on the age and flow paths of water reaching the basin outlet. Previous studies of stormflow generation in a small forested basin on the Canadian Shield used isotopic (IHS) and geochemical hydrograph separations (GHS) to infer that some event water during snowmelt reaches the stream via subsurface pathways, and that surface water runoff is generated by direct precipitation on to saturated areas (DPSA) in the stream valley. These hypotheses were tested for rainfall inputs using simultaneous IHS (18O) and GHS (dissolved silica) of basin stormflow, supplemented by hydrochemical and hydrometric data from throughflow troughs installed on basin slopes. Comparison of pre-event and subsurface water hydrographs did not provide conclusive evidence for subsurface movement of event water to the stream, owing to the appreciable uncertainty associated with the hydrograph separations. However, IHSs of runoff at the soil–bedrock interface on basin slopes indicated that event water comprised 25–50% of total runoff from areas with deep soil cover, and that these contributions supplied event water flux from the basin in excess of that attributable to DPSA. The surface water component of stormflow estimated from the GHS was also largely the result of DPSA. GHS assumes that dissolved silica is rapidly and uniformly taken up by water infiltrating the soil and that water moving via surface pathways retains the low dissolved silica level of rainfall; however, neither assumption was supported by the hillslope results. Instead, results suggest that the observed depression of silica levels in basin stormflow previously attributed to dilution by DPSA was partly a function of transport of dilute event water to the channel via preferential pathways. Implications of these results for the general use of simultaneous IHS and GHS to infer hydrological processes are discussed.

Effects of flow regulation on hydrologic patterns of a large, inland delta

The Peace–Athabasca River Delta (PAD) is one of the largest freshwater deltas and most biologically productive in the world. Because regional evaporation is greater than precipitation, the thousands of lakes and wetlands dotting this area rely on periodic flooding from the Peace and Athabasca rivers to be replenished. Flood frequency significantly declined beginning in the mid-1970s, several years after the initiation of flow regulation of the Peace River. However, the drying trend was interrupted in 1996 when the PAD experienced extensive inland inundation on two separate occasions, one in the spring and one in the summer. A one-dimensional numerical hydrodynamic model was used to evaluate the role of flow regulation and hydroclimatic conditions on the water levels of major lakes found in the PAD. Three Peace River flow scenarios were analysed: the observed flows, the flow regime without the ‘precautionary drawdown’ spill which was required because of the discovery of a sinkhole at the crest of the dam, and the naturalized flow regime, which assumed no dam regulation. Modelling results indicated that the effect of the spill on the flow regime within the PAD was approximately equivalent in magnitude, although different in timing, to what would have resulted from the prevailing hydroclimatic conditions in an unregulated system. Furthermore, even in the absence of the precautionary drawdown spill, the lake levels would have risen well above the maximum daily average, suggesting that 1996 was one of the wettest years on record. Finally, the hydrodynamic regime observed at the end of the summer 1996 was very similar to that modelled under unregulated flow conditions, suggesting that flow regulation could be used to alter the hydrodynamic regime of a large delta to at least partially restore natural conditions and potentially improve ecosystem health. Copyright

Hydrologic assessment of an inland freshwater delta using multi‐temporal satellite remote sensing

The Peace-Athabasca Delta (PAD) is located in the northern extreme of Alberta, Canada and is one of the worlds largest freshwater inland deltas. This complex and dynamic ecosystem has undergone substantial change over the last 25 years, primarily as a result of alterations to the hydrologic regime. The remoteness of the region, along with a shortage of hydrologic and ecological information, has necessitated the development of innovative methods, based on the use of satellite imagery, to assess these changes. Specialized image classification schemes were employed to derive a sixteen-year historical database of changes in water area on large lakes and isolated small basins within the delta. The time series for the large lakes has been used to quantify their hypsometric characteristics, information crucial to defining storage terms for hydraulic flow models of the delta, particularly at high stage conditions that involve over-bank flooding. Analysis of the perched basins has proven that, even with the relatively coarse resolution of LANDSAT images, satellite remote sensing of water conditions in the myriad of PAD riparian basins is a viable technique for hydrologic and ecological monitoring. The satellite derived time-series record of water levels on Jemis Lake has also permitted the first independent validation of the perched-basin water-balance model recently developed for use in assessing water-management options for the PAD. Recommendations for future research using RADARSAT are also noted.

An Overview of Temporary Stream Hydrology in Canada

Temporary streams lack streamflow at some time in the seasonal cycle, and include ephemeral, intermittent and episodic streams. They often serve as headwaters for the perennial stream network in a drainage basin, and given that headwater streams can comprise the majority of the drainage network, temporary streams are significant hydrologic features across the country. Nevertheless, they have received relatively little attention compared to perennial streams. In addition, much previous work on temporary streams has focussed on semi-arid and arid landscapes where annual evapotranspiration exceeds annual precipitation. While such climatic conditions do control the occurrence of temporary streams in some regions in Canada, temporary streams can also occur in sub-humid and humid climates. This paper examines the major controls on the occurrence and behaviour of temporary streams at the regional and reach scales in Canada; however, where necessary we also review literature from outside Canada on aspects of temporary streams relevant to the Canadian context. The paper assesses the temporal dynamics of temporary streams, along with key aspects of their geomorphology and ecology as well as current monitoring and modelling approaches. Temporary streams are very sensitive to anthropogenic and natural activities that can modify their hydrology and hydroecology, and they deserve greater attention from the Canadian hydrological community. Improved monitoring and process studies should be pursued in Canada.

Restoring ice-jam floodwater to a drying Delta ecosystem

Abstract Overbank flooding is essential to the ecological health of riparian landscapes, particularly river deltas. One of the worlds largest freshwater deltas, the Peace-Athabasca Delta (PAD) in northern Canada, has experienced a series of wetting and drying cycles because of inter-annual variations in flooding. Recent research has found that most of the major floods affecting this system are produced by spring ice jams. For approximately two decades, however, the combination of climatic and flow-regulation effects precluded significant ice-jam flooding of the PAD. Resultant drying caused major changes to the ecology of the delta and led to the evaluation of a number of methods to restore water flows. Since most of delta is contained within a national park (Wood Buffalo National Park), a major goal was to employ non-structural measures. Hence, in an effort to manage the water problems of this delta, the final report of a multi-agency “Northern River Basins Study” made the recommendation that the spring flow-release strategy of the upstream hydro electric reservoir be modified to increase the probability of ice-jam flooding near the PAD. This was to be conducted in years when downstream hydrometeorological conditions (snowpack magnitude and ice-cover strength) appeared conducive to ice-jam formation. Such favourable conditions developed in the spring of 1996, a natural ice jam began to develop, and regulated flows were increased to assist in potential flooding. As a result, the PAD experienced its first major flood in over 20 years. This paper reviews the hydrometeorological conditions that led to the ice-jam formation, compares the conditions to historical events, analyzes the spatial extent of the flood, and evaluates the effectiveness of the flow release.

Flood processes in Canada: Regional and special aspects

This paper provides an overview of the key processes that generate floods in Canada, and a context for the other papers in this special issue – papers that provide detailed examinations of specific floods and flood-generating processes. The historical context of flooding in Canada is outlined, followed by a summary of regional aspects of floods in Canada and descriptions of the processes that generate floods in these regions, including floods generated by snowmelt, rain-on-snow and rainfall. Some flood processes that are particularly relevant, or which have been less well studied in Canada, are described: groundwater, storm surges, ice-jams and urban flooding. The issue of climate change-related trends in floods in Canada is examined, and suggested research needs regarding flood-generating processes are identified.

Climate Impacts on Northern Canada: Regional Background

Abstract Understanding the implications of climate change on northern Canada requires a background about the size and diversity of its human and biogeophysical systems. Occupying an area of almost 40% of Canada, with one-third of this contained in Arctic islands, Canadas northern territories consist of a diversity of physical environments unrivaled around the circumpolar north. Major ecozones composed of a range of landforms, climate, vegetation, and wildlife include: Arctic, boreal and taiga cordillera; boreal and taiga plains; taiga shield; and northern and southern Arctic. Although generally characterized by a cold climate, there is an enormous range in air temperature with mean annual values being as high as −5°C in the south to as low as −20°C in the high Arctic islands. A similar contrast characterizes precipitation, which can be >700 mm y−1 in some southern alpine regions to as low as 50 mm y−1 over islands of the high Arctic. Major freshwater resources are found within most northern ecozones, varying from large glaciers or ice caps and lakes to extensive wetlands and peat lands. Most of the Norths renewable water, however, is found within its major river networks and originates in more southerly headwaters. Ice covers characterize the freshwater systems for multiple months of the year while permafrost prevails in various forms, dominating the terrestrial landscape. The marine environment, which envelops the Canadian Arctic Archipelago, is dominated by seasonal to multiyear sea ice often several meters thick that plays a key role in the regional climate. Almost two-thirds of northern Canadian communities are located along coastlines with the entire population being just over 100 000. Most recent population growth has been dominated by an expansion of nonaboriginals, primarily the result of resource development and the growth of public administration. The economies of northern communities, however, remain quite mixed with traditional land-based renewable resource-subsistence activities still being a major part of many local economies.

Establishing Standards and Assessment Criteria for Ecological Instream Flow Needs in Agricultural Regions of Canada

Agricultural land use can place heavy demands on regional water resources, strongly influencing the quantity and timing of water flows needed to sustain natural ecosystems. The effects of agricultural practices on streamflow conditions are multifaceted, as they also contribute to the severity of impacts arising from other stressors within the river ecosystem. Thus, river scientists need to determine the quantity of water required to sustain important aquatic ecosystem components and ecological services, to support wise apportionment of water for agricultural use. It is now apparent that arbitrarily defined minimum flows are inadequate for this task because the complex habitat requirements of the biota, which underpin the structure and function of a river ecosystem, are strongly influenced by predictable temporal variations in flow. We present an alternative framework for establishing a first-level, regional ecological instream flow needs standard based on adoption of the Indicators of Hydrologic Alteration/Range of Variability Approach as a broadly applicable hydrological assessment tool, coupling this to the Canadian Ecological Flow Index which assesses ecological responses to hydrological alteration. By explicitly incorporating a new field-based ecological assessment tool for small agricultural streams, we provide a necessary verification of altered hydrology that is broadly applicable within Canada and essential to ensure the continuous feedback between the application of flow management criteria and ecological condition.

Multivariate Modelling of Water Temperature in the Okanagan Watershed

Initiatives for the protection of river ecosystems must include the monitoring of key flow and water quality variables, as well as clear and quantifiable management goals. One variable which strongly influences water quality is water temperature, and its modification arising from human activity should be incorporated into ecosystem protection guidelines. This work, conducted as part of the Canadian National Agri-Environmental Standards Initiative (NAESI) program, presents a preliminary study investigating statistical regression methods and a geostatistical approach to model key water temperature characteristics that could assist in the development of standards. Water temperature time series recorded at 16 sites in the Okanagan watershed were used to develop the models. Monthly maxima were modelled for the period of April-September 2007 using four predictors: the site longitude, the drainage basin maximum altitude, the local slope at the station, and the log of the mean substrate diameter. Four types of multivariate regressions of monthly maxima were produced, and a leave-one-out resampling approach was used to validate the models. Relative Bias, Root Mean Square Errors (RMSE) and a corrected Akaike Information Criterion (AICc) were calculated for each month. Models gave RMSE values between 0.9°C and 2.1°C for the monthly maxima. All models generally performed best between May and July. Geostatistical interpolation of maxima was also performed in a multivariate physiographic space reduced to two orthogonal dimensions using canonical correlation analysis (CCA). Examples of interpolated maps show that the approach can be used to discriminate between warm and cool streams.