The Carnation Creek project is a long-term study of the effects of forestry practices on a small coastal watershed (11 km 2 ) located in southwestern Vancouver Island. Initiated in 1970, this pretreatment versus post-treatment case study consists of 5 years of preharvest, 6 years of duringharvest, and now, 34 years of postharvest research. Forty-one percent of the watershed was clearcut from 1976 to 1981. One tributary sub-basin (1.1 km 2 ) was left as an unharvested reference drainage. Riparian treatments varied from clearcuts to a variable-width buffer. Fish population responses to logging have been complex, and specific to species and life stages. Stream warming due partly to riparian harvest increased the growth and survival of juvenile coho salmon and elevated smolt production by 65% for nearly three decades. These relatively short-term thermal benefits offset the effects of riparian clearcutting which included accelerated bank erosion, streambed scour, loss of stable in-stream wood, and sediment movement downstream. Landslides in 1984 greatly amplified these effects but took more than 20 years to propagate downstream to reduce fish habitat complexity and increase streambed instability and sediment transport over the entire portion inhabited by anadromous salmon. These delayed impacts have surpassed the thermal-related benefits for coho salmon. Fry-to-smolt overwinter survival has declined from a mean of 50% between 1982 and 2004 to 15% since 2005. Coho salmon smolt production has consequently been reduced to below prelogging levels. Results show that forestry-related alterations may take decades to fully develop and persist for decades longer without watershed and stream channel restoration.

Stream channel morphology forms the template upon which hydraulic aspects of aquatic habitat are created, yet spatial and temporal variability in habitat imposed by changing morphology is not well understood. This paper presents a conceptual model linking sediment supply patterns to spatial and temporal variability in channel form and aquatic habitat. To evaluate this model, change over time in three habitat variables is quantified using a 2D hydrodynamic modeling approach. A 45‐year record of topographic data from Carnation Creek, a catchment in coastal British Columbia, is used for the flow modeling. Using the Nays2DH modeling platform, water depths and velocities are simulated in eight channel segments located at different positions relative to locations of historical colluvial input using seven flow levels ranging from 3% to 400% of mean annual discharge (0.02 to 3.31 m 3s −1). Results indicate that habitat availability changes through time as a result of sediment supply‐driven changes to channel morphology and wood loads, but patterns in habitat vary as a function of dominant channel segment morphology. Spatial and temporal variability in morphology also influences the relationship between habitat availability and river discharge, leading to non‐stationary habitat‐discharge rating curves. When habitat areas are predicted by applying these curves to daily flow series spanning annual dry seasons, over 50% of the variance in cumulative seasonal habitat area can be explained by year‐to‐year changes in channel morphology and wood loading, indicating that changing morphology is an important factor for driving temporal habitat variability. This variance is related to the morphological variability of a channel segment, which in turn is associated with the segment position relative to zones of colluvial input. Collectively, these results suggest that variability in habitat is impacted by channel morphology, and can be evaluated partly on the basis of a channel's sediment supply regime. © 2019 John Wiley & Sons, Ltd.

This paper reviews potential effects of forest management on low flows in snowmelt-dominated hydrologic regimes. The hydrologic response of low flows to forest management was found to be highly variable in magnitude, time, and space. Forest management generally increases water volume—no case studies relevant to snowmelt-dominated regimes reported a decrease in water quantity as a result of forest harvesting. In areas where fog drip occurs, a decrease in water volume contributing to low flows might be observed. The longevity of increased water quantity is infrequently discussed in the literature specific to snowmelt dominated regimes. A few authors, however, have commented on expected longevity of response based upon analysis of literature not specific to snowmelt-dominated regimes. These authors generally report a return to pre-treatment low flow levels within 3–6 years with the re-establishment of vegetation.The review identifies many knowledge, research, and extension needs. Knowledge of low flows is hampered by an incomplete understanding of generation processes, particularly those relating to subsurface flow, evapotranspiration, and the interrelated effects of forest practices and climate change. Forest management is only one of many human activities that can potentially affect a watershed�s hydrologic regime. Because natural processes and human activities occur simultaneously, studying the sole effects of forest management on low flows is difficult. Limitations in low flow science around measurement methodologies, scaling of results, and inadequate research design are noted.

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.

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