H. J. van Meerveld

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.

Topographic controls on shallow groundwater levels in a steep, prealpine catchment: When are the TWI assumptions valid?

Topographic indices like the Topographic Wetness Index (TWI) have been used to predict spatial patterns of average groundwater levels and to model the dynamics of the saturated zone during events (e.g., TOPMODEL). However, the assumptions underlying the use of the TWI in hydrological models, of which the most important is that groundwater level variation can be approximated by a series of steady state situations, are rarely tested. It is also not clear how well findings from existing hillslope studies on sites with transmissive soil can be transferred to entire catchments with less permeable soils. This study, therefore, evaluated the suitability of selected topographic indices to describe spatial groundwater level variations based on time series from 51 groundwater wells in a 20 ha catchment with low-permeability soils in Switzerland. Results showed that median groundwater levels were correlated to slope, curvature, and TWI, but the strength of correlation depended on whether the indices characterized the local topography or the topography of the upslope contributing area. The correlation between TWI and groundwater levels was not constant over time but decreased at the beginning of rainfall events, indicating large spatial differences in groundwater responses, and increased after peak flow, when groundwater levels could be considered to be spatially in a steady state. Our findings indicate that topographic indices are useful to predict median groundwater levels in catchments with low-permeability soils and that the TWI assumptions are best met when groundwater levels change slowly.

Controls on sediment production from an unpaved resource road in a Pacific maritime watershed

Unpaved resource roads have the potential to produce large amounts of sediment and can negatively impact water quality and aquatic ecology. In order to better understand the dominant controls on sediment generation from unpaved resource roads, we did 23 large-scale rainfall simulation experiments on a road section in the Honna Watershed, Haida Gwaii, British Columbia, Canada. The experiments were performed with different rainfall intensities (4–52 mm/h), with and without traffic. Precipitation intensity was the dominant control on the amount of sediment generated from the road surface; the total mass of sediment increased linearly with precipitation intensity. The number of passages of loaded logging trucks during an experiment was the second most dominant control on the total amount of sediment generated from the road surface. Elevated sediment concentrations in road surface runoff persisted for 30 min following the passage of loaded logging trucks during low intensity (<8 mm/h) rainfall events and for much shorter periods at higher rainfall intensities. The mass of sediment generated by the passage of a loaded truck increased with precipitation intensity. Passages of empty logging truck did not result in sediment pulses, except during very high rainfall intensities. Seven small-scale rainfall simulation experiments on other parts of the road, however, highlight the large spatial variability in sediment production from the road surface, suggesting additional experiments are required to better describe and predict sediment production from different road sections.

Topographic Controls on Deep Groundwater Contributions to Mountain Headwater Streams and Sensitivity to Available Recharge

An important, yet poorly understood, influence on the hydrologic behaviour of mountain headwater streams is deep groundwater (DG) flow, which circulates at depth through the bedrock system and discharges to surface water or shallow groundwater at stream valleys. In this study, two- and three-dimensional hydrogeological models were generated for both generic and real topography. DG contribution areas were delineated using groundwater pathline analysis, and the sensitivity of DG discharge at headwater stream valleys due to changes in applied recharge was investigated. For some streams, the 3-D nested nature of topographically-driven DG flow results in groundwater that is recharged within one headwater stream catchment bypassing the associated stream valley and emerging as DG discharge in a different, relatively deeper stream valley. Contributing areas of DG to headwater streams are thus more complex than would be predicted based on catchment boundaries alone. Differences in DG discharge and DG contributing areas in response to changes in applied recharge are a reflection of differences in topography and suggest that headwater streams within the same watershed differ in their sensitivity to changes in recharge. A small, but significant, temporal response of DG discharge to a change in recharge is found to occur within a 1 to 3 year timeframe, highlighting the importance of variations in DG discharge for stream hydrology. The modelling approach used in this study requires only digital elevation model data, and thus can be used in regions of limited data and in ungauged basins to provide a preliminary indication of relative stream sensitivity to long-term changes in recharge as a result of climate change, forest management practices, or groundwater extraction.

Impacts of rural water diversions on prairie streamflow

Prairie streams have low basin-average runoff, and are significantly impacted by human settlement. Recent studies have suggested that climate change has resulted in a 0.2% per year decrease in southern Albertas late summer streamflow. However, even in river basins identified by the Water Survey of Canada as having natural flow, more than 5% of the total runoff may be diverted and stored for rural activities. This is often unaccounted for in hydrological models or statistical analyses of streamflow trends. While the cumulative impact of these small water diversions is now recognized in water management decisions for major basins, it has not yet been incorporated into streamflow analyses. This paper highlights the cumulative effects of small water diversions and illustrates that they are at least as large as reported climate change effects, and must be accounted for in any streamflow analysis of Prairie streams.

Zeroflow: A pub (prediction in ungauged basins) workshop on temporary streams: Summary of workshop discussions and future directions

1 Environment Canada @ W-CIRC, University of Victoria, Victoria, BC V8W 3R4. 2 Department of Geography, University of Lethbridge, Lethbridge, AB T1K 3M4. 3 Department of Geography, Simon Fraser University, Burnaby, BC V5A 1S6. 4 Environment Canada, Saskatoon, SK S7N 3H5. 5 Faculty of Earth and Life Sciences, VU University Amsterdam, Amsterdam, 1081 HV, The Netherlands. 6 Environment Canada, Vancouver, BC V6C 3S5. * Membership in CWRA or CSHS.

Intermittent and Perennial Streamflow Regime Characteristics in the Okanagan

Streamflow data from ten Water Survey of Canada gauging stations were analyzed to characterize streamflow regimes in the Okanagan Basin (British Columbia). The differences in the streamflow regime characteristics of the perennial and intermittent streams were subtle, except for the obvious difference in summer low flows. The intermittent streams tended to have faster recessions after spring freshet, steeper flow duration curves, a slightly earlier median day of the year of the start of the freshet, and more variable discharge in fall. In years with high fall precipitation, discharge was also high during fall for the intermittent streams but in other years it was very low. Discharge on August 15th was lower or similar to streamflow on March 15th for the intermittent stream, whereas it was much higher on August 15th for the perennial streams. These subtle streamflow regime differences point to differences in flow pathways, groundwater contributions to streamflow, and residence times between the intermittent and perennial watersheds, and may have important ecological implications.

Laggs can develop and be restored inside a raised bog

The lagg is an integral part of the hydrological system of a raised bog and can add significantly to the biological diversity of the ecosystem. Conservation and restoration of raised bogs should therefore involve this transition zone. The ideal situation for conservation is to protect or restore the natural lagg at the outside margin of the bog. However, it is not always possible to restore the lagg where it was historically situated. An analysis of historic maps of a raised bog in British Columbia, Canada, shows that in areas where the outflow of water from the bog has been impeded, lagg plant communities have naturally colonized parts of the bog that were historically open bog. This suggests that it is possible to create the ecohydrological conditions of a lagg in areas that are currently occupied by bog species. Based on this knowledge and the hydrochemical, hydrological, and vegetative characteristics of a regionally-specific lagg reference ecosystem, we describe several lagg restoration options for locations where it is not possible to restore the lagg at the outside margin of the bog.

Upper and lower benchmarks in hydrological modelling

Whenassessing theperformanceofahydrologicalmodel, aquestionthat can be raised is, how good is really good? Despite several calls to use benchmarks (Pappenberger, Ramos, Cloke, & Fredrik, 2014; Schaefli & Gupta, 2007; Seibert, 2001), model performance in the scientific literature, conference presentations, and discussions among hydrological modellers is still often solely judged based on the value of some performancemeasure.Forinstance,amodelisratedaswell‐performingbecause model efficiency (Nash & Sutcliffe, 1970) values are above 0.7. Some authors (e.g., Moriasi et al., 2007; Ritter & Muñoz‐Carpena, 2013) even suggestperformance classes basedonmodel efficiencyvalues.Basedon our experiences with the application of hydrological models for catchmentswith largely varying characteristics,we argue that such judgments on model performance can only be made if model performances are relatedtobenchmarksthatrepresentwhatcouldandshouldbeexpected. The idea of using benchmarks is by no means new and actually the most commonly used performance measure in hydrological modelling, the model efficiency or Nash‐Sutcliffe efficiency (Nash & Sutcliffe, 1970), can be interpreted as the comparison of model simulations with a constant streamflow equal to the observed mean streamflow (lower benchmark) and a perfect fit (upper benchmark). Obviously, this lower benchmark is not too hard to beat, whereas this upper benchmark is hardly achievable in practice. To better evaluate how good model simulations are, more informative lower benchmarks have been suggested (Garrick, Cunnane, & Nash, 1978; Schaefli & Gupta, 2007; Seibert, 2001). However, the use of benchmarks that are taking into account what is possible with the data, that is, what could and should be expected, is still not common practice in hydrological modelling. In hydrological modelling, it is never possible to obtain a perfect model fit. This is partly due to the complexity of processes in nature but also due to errors in observations of the driving data and streamflow. Therefore, the upper benchmark should not be an unrealistic perfect simulation but take potential errors in the data into account. On the other hand, there is usually also a lower limit on how bad a model can be, simply because the driving data ensure that

Groundwater similarity across a watershed derived from time‐warped and flow‐corrected time series

Information about catchment-scale groundwater dynamics is necessary to understand how catchments store and release water and why water quantity and quality varies in streams. However, groundwater level monitoring is often restricted to a limited number of sites. Knowledge of the factors that determine similarity between monitoring sites can be used to predict catchment-scale groundwater storage and connectivity of different runoff source areas. We used distance-based and correlation-based similarity measures to quantify the spatial and temporal differences in shallow groundwater similarity for 51 monitoring sites in a Swiss prealpine catchment. The 41 months long time series were preprocessed using Dynamic Time-Warping and a Flow-corrected Time Transformation to account for small timing differences and bias toward low-flow periods. The mean distance-based groundwater similarity was correlated to topographic indices, such as upslope contributing area, topographic wetness index, and local slope. Correlation-based similarity was less related to landscape position but instead revealed differences between seasons. Analysis of variance and partial Mantel tests showed that landscape position, represented by the topographic wetness index, explained 52% of the variability in mean distance-based groundwater similarity, while spatial distance, represented by the Euclidean distance, explained only 5%. The variability in distance-based similarity and correlation-based similarity between groundwater and streamflow time series was significantly larger for midslope locations than for other landscape positions. This suggests that groundwater dynamics at these midslope sites, which are important to understand runoff source areas and hydrological connectivity at the catchment scale, are most difficult to predict.