Streamline Article Index 1996-2013

Watershed restoration and management in British Columbia, 1996 to 2013.

Effects of Forest Harvesting on Warm-Season Low Flows in the Pacific Northwest: A Review

Paired-catchment studies conducted on small (< 10 km2) rain-dominated catchments revealed that forest harvesting resulted in a period of increased warm-season low flows ranging from less than five years to more than two decades, consistent with the results of stand-level studies and process considerations. Of the five paired-catchment studies in snow-dominated regions, none revealed a statistically significant change in warm-season low flows in the first decade following harvest, although two exhibited non-significant higher flows in August and September and one had lower flows. Two studies, one of rain-dominated catchments and one of snow-dominated catchments, found that summer low flows became more severe (i.e., lower) about two decades or so following harvest. These longer-term results indicate that indices such as equivalent clearcut area, as currently calculated using monotonic recovery curves, may not accurately reflect the nature of post-harvest changes in low flows. Studies focussed on medium to large catchments (tens to thousands of km2 in area) found either no statistically significant relations between warm-season low flows and forest disturbance, or inconsistent responses. Attempts to synthesize existing studies are hampered by the lack of a common low-flow metric among studies, as well as detailed information on post-harvest vegetation changes. Further fieldresearch and process-based modelling is required to help elucidate the underlying processes leading to the results from these paired-catchment studies and to enhance the ability to predict streamflow responses to forest harvesting, especially in the context of a changing climate. KEYWORDS: streamflow; forestry; low flows; fish habitat; hydrologic recovery

Key Planning Questions to Consider in Small Stream Hydrometric Monitoring

This article provides key questions to consider when planning and operating a small stream hydrometric station. Office planning components include defining hydrometric monitoring objectives; the availability of hydrometric expertise; resource availability; safety plans and standard operating procedures; equipment availability (hydrometric station installation and streamflow measurement); sampling frequency and data availability; permissions and permitting requirements; data processing, access, and archiving; and metadata requirements. Key parts of field-based hydrometric planning include site safety; site accessibility; flow variability; channel control features; flow containment, diversions and additions; low flow considerations; high flow considerations; flow measurement challenges in small streams; benchmarks and survey criteria; and public safety and vandalism. Theoverall goal of the article is to help non-professionals collect better hydrometric data and to highlight the varied planning aspects of typical hydrometric installations and operations.

The Role of the Hydrographer in Rating Curve Development

Stage-discharge rating curves are used to produce most of the world’s discharge data. The shape of these curves is dependent on the shape of the channel that controls flow. Changes in rating curves occur over time in response to transitory (e.g., vegetation, ice, debris) or persistent (e.g., aggradation/degradation) changes of the rated channel. Errors in rating curve development can result from the mischaracterization of the shape of the curve at a given time, or the misidentification of patterns of change over time. While data-driven methods for rating curve calibration are desirable, conventional statistical regression techniques, unfortunately, require far more data points to fully characterize the patterns of change in the curve shapes than are commonly available. This article discusses the benefits of field observations of the stream channel in support of rating curve development. The mathematical form of the rating curve can be inferred from observations of natural channel control features that link to principles of flow. In this article, the theoretical components of the rating curve equation are discussed with emphasis on how field observations can be used to groundtruth calibrated values for the coefficient, offset, and exponent for each segment of a stage-discharge rating curve. The article also explains how conceptual models developed by the hydrographer add value to the calibration process.

The Role of the Hydrographer in Rating Curve Development

Stage-discharge rating curves are used to produce most of the world’s discharge data. The shape of these curves is dependent on the shape of the channel that controls flow. Changes in rating curves occur over time in response to transitory (e.g., vegetation, ice, debris) or persistent (e.g., aggradation/degradation) changes of the rated channel. Errors in rating curve development can result from the mischaracterization of the shape of the curve at a given time, or the misidentification of patterns of change over time. While data-driven methods for rating curve calibration are desirable, conventional statistical regression techniques, unfortunately, require far more data points to fully characterize the patterns of change in the curve shapes than are commonly available. This article discusses the benefits of field observations of the stream channel in support of rating curve development. The mathematical form of the rating curve can be inferred from observations of natural channel control features that link to principles of flow. In this article, the theoretical components of the rating curve equation are discussed with emphasis on how field observations can be used to groundtruth calibrated values for the coefficient, offset, and exponent for each segment of a stage-discharge rating curve. The article also explains how conceptual models developed by the hydrographer add value to the calibration process.

A Review of Free Optical Satellite Imagery for Watershed-Scale Landscape Analysis

Watershed-scale landscape analysis includes many disciplines, including ecological, hydrological, and geographical sciences. The recent proliferation of free optical satellite imagery (FOSI) has changed the possibilities for the monitoring of environmental change at local and global scales. Many reviews exist for discipline-specific remote sensing applications; however, this article seeks to highlight the rapidly growing archive of FOSI and applied tools that can be used by all levels of users. Herein, ten techniques and eight applications of FOSI are reviewed, along with the specifications and limitations of various sources of FOSI. Although this review focuses on Western Canada, the democratization of FOSI is globally relevant, and the objective is to explain basic concepts via figures and reference materials to help summarize this rapidly changing field.

Summary of the Forests and Water Workshop

With population growth, climate change, and increasing forest disturbance, understanding the complex relationships between forests and water is key to sustaining future forest resources, aquatic habitat, and water supplies. Research into forest and water interactions continues to expand our understanding of ecohydrological processes and our ability to assess the hazards associated with natural and human-related forest disturbances.

Efficient Semi-Distributed Hydrological Modelling Workflow for Simulating Streamflow and Characterizing Hydrologic Processes

Streamflow records are required for a wide range of industrial, environmental, and urban applications. However, the sparse coverage of hydrometric stations in western Canada, and their limited spatial and temporal representativeness, necessitate hydrologic regionalization methods to generate streamflow for a point of interest. Here, an efficient semi-distributed hydrological modelling workflow is presented which has modest data requirements, uses publicly available data sources, and applies free open-source software. The method is scalable, relies on few statistical assumptions, and is scientifically rigorous. In addition, the resultant model allows the ability to trace the primary contributors of streamflow in the region, and for the evaluation of future watershed hydrology due to environmental and climatic change.

Quantifying the Relation Between Electrical Conductivity and Salt Concentration for Dilution Gauging Via Dry Salt Injection

Salt dilution is a popular approach used for discharge measurement. This research focused on the procedure for determining the calibration factor (CFT) that is used to convert measured temperature corrected electrical conductivity to salt concentration for injection using dry salt. It is important to document the uncertainty in CFT because it contributes directly to uncertainty in the calculated discharge. Based on laboratory trials, it was found that the calibration should be performed as close to in situ stream temperature as possible to minimize errors. The discharge measurement and calibration procedure should be performed with the same probe to minimize uncertainty. Distilled water can be used instead of stream water for a calibration solution if an analytical correction is applied to account for differences in ionic composition of the water. The calibration factor can be determined with an uncertainty of less than ± 1% under “best-case” conditions, and the uncertainty may be as high as ± 4% under less favourable conditions. If calibration is not performed, CFT can be estimated from the relation between CFT and background temperature-corrected electrical conductivity (ECBG) with an uncertainty of about ± 2%, or estimated as a set value of 0.486 mg·cm·μS-1·L-1 with an uncertainty of about ± 2.8% for a properly calibrated probe. More testing should focus on streams with ECBG > 500 μS·cm-1, which were not well represented in this study.

Why Watershed Analysts Should Use R for Data Processing and Analysis

Both the science and practice associated with watershed management involve the processing, presentation and analysis of quantitative information. In this article, the use of open source programming languages by watershed analysts is advocated. The R language, in particular, provides a rich set of tools for the types of data that are commonly encountered in watershed analysis. The utility of R is illustrated through three examples: intensity-duration-frequency analysis of rainfall data, baseflow separation, and watershed delineation and mapping.