R. D. Moore

Throughflow variability on a forested hillslope underlain by compacted glacial till

This study examined the spatial and temporal variability of throughflow in a shallow forest oil in terms of the controls exerted by topography, soil properties and the shape of the water table. Hillslope outflow was measured at nine troughs installed at a road cut, and hydraulic head was measured at 37 piezometers installed to the confining till surface at the base of the soil. At the lowest flows, the distribution of throughflow across the hillslope conformed reasonably to the distribution of upslope contributing area computed from the topography of the confining basal till layer. At higher flows, however, the distribution of throughflow shifted, partly as a result of changes in the orientation in flow tubes as the piezometric surface changed. At high flows, surface topography appeared to provide a reasonable proxy for the shape of the water table. Shunting of water through discrete macropores, however, can apparently overwhelm topographic controls on throughflow, at least for slope widths less than about 10 m. Effective hydraulic conductivities computed at the scale of the troughs varied over two orders of magnitude and displayed no consistent relationship with the thickness of the saturated layer. Estimates at the plot scale (c. 10 m hillslope width) were far less variable, and for higher flows displayed an approximately linear relationship with saturated zone thickness. Copyright

Pacific Decadal Oscillation and the Hydroclimatology of Western Canada—Review and Prospects

The Pacific Decadal Oscillation (PDO) is a large-scale climate system feature that influences the surface climate and hydrology of western North America. In this paper, we review the literature describing the PDO and demonstrate its effects on temperature, precipitation, snowfall, glacier mass balance, and streamflow with a focus on western Canada, and particularly British Columbia. We review how the PDO index was developed and discuss other North Pacific climate patterns that resemble the PDO. The impacts of PDO on glacier mass balance and streamflow from retrospective studies are also reviewed and illustrated with specific examples from BC. We assess the current state of knowledge regarding the PDO and provide a critical assessment of its use in hydroclimatology. This information should provide insight on the sensitivity of projects to climatic variability.

Stream Temperature Patterns in British Columbia, Canada, Based on Routine Spot Measurements

Spot stream temperatures recorded by Water Survey of Canada technicians during visits to gauging stations in British Columbia were used to characterize stream temperature patterns. A general linear modelling approach was used to relate the median water temperatures for each month to a set of variables describing catchment and climatic characteristics. Models were fitted for stations with drainage areas greater than 100 km2 to avoid possible regional bias, because most of the stations with areas less than 100 km2 were located south of 52°N. The final predictor variables varied by month and, for July and August, included normal monthly maximum air temperature, normal annual precipitation, mean catchment elevation, logarithm of drainage area, percent glacier cover, percent lake cover, and whether or not the flow regime is regulated. The models explained up to 79% of the variance in water temperature, with standard errors of the estimate ranging from 0.7°C in January to 1.6°C in August. Values of the coefficients for the predictor variables and their seasonal variations were consistent with the physical processes governing stream temperature. These models suggest that catchment characteristics leave an imprint on stream temperature, even for large catchments, and need to be accounted for in efforts to model regional variations in stream temperature.

Quantifying Uncertainty in Streamflow Records

Uncertainty in hydrometric data is a fact of life. Basic assumptions about the nature of this uncertainty are necessary in every analysis of hydrometric data, and an understanding of the variability of uncertainty can facilitate the effective use of hydrologic information. For most of the twentieth century there has been little change in hydrometric methods and many analysts explicitly or implicitly assume that the uncertainty has not changed over the period of record. We argue that there is substantial variability in the magnitude of uncertainty in published streamflow records that is not transparent to data users. Quantifying uncertainty is particularly important in the context of the current changes in hydrometric technology and in the increasing integration of data sets from multiple providers. We recommend best practices for identifying uncertainty in field notes and propagating that observational uncertainty through the data production process. We suggest both field and reanalysis studies that could be undertaken to improve understanding of hydrometric uncertainty. We also recommend improvements in management practices, including preservation of relevant metadata and a suitable period of overlap for new and old observing systems to allow assessment of the effects of changing technology.

Empirical modelling of maximum weekly average stream temperature in British Columbia, Canada, to support assessment of fish habitat suitability

The objective of this study was to characterize the spatial variability of stream thermal regimes in British Columbia, Canada, with the specific goal of developing a predictive model to assist in provincial-scale assessment of fish habitat. It is part of a broader study to develop an approach to support the designation of “Temperature Sensitive Streams”, particularly in relation to the potential effects of forest harvesting and climate change. Stream temperature data were collected from researchers, consultants and government agencies. After checking for data quality, the annual maximum of a seven-day running average of mean daily water temperature (MWAT) was extracted for each station-year. A multiple regression model for the mean MWAT for each station was fitted for stations having basin areas between 1 and 104 km2. Predictor variables included the logarithm of catchment area, normal July–August air temperature for the location, the square root of the percentage of glacier cover in the catchment, the square root of the percentage of lake cover in the catchment, the mean catchment elevation, channel slope, a coefficient related to intensity of the mean annual flood, and the deviation of July–August air temperature during the monitoring year(s) from the average during a reference period. Model coefficients were consistent with the physical processes known to govern stream temperature. The standard deviation of prediction errors from a 10-fold cross-validation was 2.1°C. Lack of information on riparian shading is a likely source of a significant portion of the prediction error. The model can be used to provide an initial prediction of stream temperature regime for fish habitat assessment, as well as to provide first-order estimates of the sensitivity of MWAT to climatic warming and glacier retreat.

Observations and modeling of hillslope throughflow temperatures in a coastal forested catchment

A growing body of research on stream thermal regimes has highlighted the importance of heat advection associated with surface water and groundwater interactions, such as hyporheic exchange, groundwater discharge, and hillslope throughflow inputs. Existing catchment models that predict stream temperature use a variety of approaches to estimate throughflow temperatures, but none has been evaluated against field measurements of throughflow temperature. In this study, throughflow temperatures were monitored over two winters at 50 locations adjacent to a headwater stream (11 ha catchment area) located in the rain-on-snow zone of the Pacific Northwest. Existing approaches to estimate throughflow temperature under or overpredicted throughflow temperatures by up to 5°C, or were unable to represent the influence of transient snow cover. Therefore, a conceptual-parametric model that is computationally efficient was developed that simulates hillslope hydrology and throughflow temperatures. The model structure includes an upslope reservoir that drains into a downslope reservoir that, in turn, drains into the stream. Vertical and lateral energy and water fluxes are simulated using simplified process representations. The model successfully predicts throughflow temperatures and highlights the dominant role of throughflow advection and the influence of snow cover on stream thermal regimes during high flow periods and rain-on-snow events.

Advances in Canadian Forest Hydrology, 2003-2007

Recent research in forest hydrology in Canada is reviewed, with a focus on studies of hydrological and hydrochemical processes in natural and disturbed forest landscapes during the 2003-2007 period. The value of hydrologic classification schemes for understanding these processes and guiding effective forest management practices is highlighted, as are the spatially and temporally extensive hydrologic datasets needed to test these classifications. Studies of hydrologic response to natural and anthropogenic forest disturbance are reviewed, and the strengths and limitations of paired-basin experiments for assessing forest disturbance effects on watershed processes are evaluated. Recent shifts in the context of forest hydrology research in Canada are presented, such as issues of climate warming, the mismatch between experimental and management scales, and the increasing need to address cumulative effects of both natural and anthropogenic forest disturbance.

Trends in groundwater levels in British Columbia

The relations between groundwater level fluctuations and past climatic variations are explored using available data from the provincial observation well network, climate data and hydrometric data from the two major hydro-climatic zones of British Columbia. The majority of these well records start in the late 1970s or 1980s, providing only 20 to 30 years of record at most, and only a few of these wells monitor aquifers in “pristine” areas that reflect natural variability; the others have been influenced by human activity. Mean monthly groundwater levels were used to manually classify the wells into rainfall- and snowmelt-dominated seasonal cycles. Temporal trends of groundwater levels and a simple recharge measure were calculated using the non-parametric Spearman’s rank correlation coefficient over a common period from 1976–1999. This period was selected to coincide with the positive phase of the Pacific Decadal Oscillation (PDO) so as to eliminate the potential impact a shift in the PDO might have on groundwater levels and recharge trends. Overall, late summer groundwater levels appear to have lowered across the province. Trends in recharge were more variable with both positive and negative trends. However, most of the trend results were non-significant. This assessment was complicated by the varied nature of the climate in different parts of the province, which determines the hydrologic regime (pluvial, nival, glacierized, mixed), the complexity of the groundwater system as it relates to the connection between groundwater and surface water, and the remote sources of many rivers in the mountainous regions of the province. Les relations entre les fluctuations des niveaux des eaux souterraine et les variations climatiques passées sont explorées à l’aide des données disponibles provenant du réseau piézométrique provincial, des données climatiques et des données hydrométriques des deux principales zones hydroclimatiques de la Colombie-Britannique. Ces registres de puits ont été lancés pour la plupart vers la fin des années 1970 ou dans les années 1980, ce qui nous donne seulement entre 20 et 30 années d’enregistrements tout au plus, et seuls quelques-uns de ces puits permettent de surveiller les aquifères dans des zones « vierges » qui reflètent la variabilité naturelle; les autres ayant subi l’influence de l’activité humaine. Les niveaux mensuels moyens des eaux souterraines ont été utilisés pour classer manuellement les puits en cycles saisonniers dominés par les précipitations et la fonte des neiges. Les tendances temporelles des niveaux des eaux souterraines et une simple mesure de l’alimentation en eau souterraine ont été calculées à l’aide du coefficient de corrélation de rang de Spearman non paramétrique sur une période commune allant de 1976 à 1999. Cette période a été sélectionnée afin qu’elle coïncide avec la phase positive de l’oscillation décennale du Pacifique (ODP) de façon à éliminer l’incidence éventuelle qu’un changement dans l’ODP pourrait avoir sur les niveaux des eaux souterraines et sur les tendances en matière d’alimentation. Dans l’ensemble, les niveaux des eaux souterraines vers la fin de l’été semblent avoir diminué partout dans la province. Les tendances en matière d’alimentation de la nappe souterraine étaient plus variables, celles-ci pouvant être tant positives que négatives. Cependant, la plupart des résultats liés aux tendances étaient non significatifs. Cette évaluation a été compliquée par des facteurs comme la nature variée du climat dans différentes parties de la province, lequel détermine le régime hydrologique (pluvial, nival, englacé, mixte), la complexité du système aquifère en ce qu’il se rapporte à la relation entre les eaux souterraines et les eaux de surface, et les sources éloignées de nombreuses rivières dans les régions montagneuses de la province.

Correction to Detection of runoff timing changes in pluvial, nival, and glacial rivers of western Canada

[1] Changes in air temperature, precipitation, and, in some cases, glacial runoff affect the timing of river flow in watersheds of western Canada. We present a method to detect streamflow phase shifts in pluvial, nival, and glacial rivers. The Kendall-Theil robust lines yield monotonic trends in normalized sequent 5-day means of runoff in nine river basins of western Canada over the period 1960–2006. In comparison to trends in the timing of the date of annual peak flow and the center of volume, two other less robust metrics often used to infer streamflow timing changes, our approach reveals more detailed structure on the nature of these changes. For instance, our trend analyses reveal extension of the warm hydrological season in nival and glacial rivers of western Canada. This feature is marked by an earlier onset of the spring melt, decreases in summer streamflow, and a delay in the onset of enhanced autumn flows. Our method provides information on streamflow timing changes throughout the entire hydrological year, enhancing results from previous methods to assess climate change impacts on the hydrological cycle.

Variability of tracer breakthrough curves in mountain streams: Implications for streamflow measurement by slug injection

Tracer dilution methods are commonly used to measure discharge in steep mountain streams. This research addressed knowledge gaps associated with dilution methods using original field data collected on nine streams in southwest British Columbia and discharge measurements conducted by Northwest Hydraulic Consultants Ltd. Minimum mixing lengths ranged between 2.4 and 24.5 stream wetted widths, but determining the mixing length can be confounded by surface-subsurface water fluxes. Probes need to be placed on opposite sides of the stream to verify adequate mixing, because probes located at different locations on the same of the stream sometimes suggested complete mixing had occurred when it in fact had not. For probes located downstream of complete mixing, breakthrough curves (BTCs) for probes located in the main current differed significantly from probes in zones with recirculating flow, even though they yielded discharge values within ± 10%. The peak of the BTC is a function of the mass of tracer injected, reach length, channel cross-sectional area, and the integral of a non-dimensional BTC, A*. The distribution of A* derived from analysis of 175 BTCs can be used, in conjunction with estimates of channel geometry and desired increases in electrical conductivity, to estimate dosing requirements to avoid under- or over-dosing a stream reach.