By Robbie S.H. Johnson and Younes Alila
Drawing on advances in non-stationary frequency analysis and the science of causation and attribution, this study employs a newly developed non-stationary stochastic paired watershed approach to determine the effect of forest harvesting on snowmelt-generated floods. Moreover, this study furthers the application of stochastic physics to evaluate the environmental controls and drivers of flood response. Physically-based climate and time-varying harvesting data are used as covariates to drive the non-stationary flood frequency distribution parameters to detect, attribute, and quantify the effect of harvesting on floods in the snow-dominated Deadman River (878 km2) and nested Joe Ross Creek (99 km2) watersheds. Harvesting only 21% of the watershed caused a 38% and 84% increase in the mean but no increase in variability around the mean of the frequency distribution in the Deadman River and Joe Ross Creek, respectively. Consequently, the 7-year, 20-year, 50-year, and 100-year flood events became approximately two, four, six, and ten times more frequent in both watersheds. An increase in the mean is posited to occur from an increase in moisture availability following harvest from suppressed snow interception and increased net radiation reaching the snowpack. Variability was not increased because snowmelt synchronization was inhibited by the buffering capacity of abundant lakes, evenly distributed aspects, and widespread spatial distribution of cutblocks in the watersheds, preventing any potential for harvesting to increase the efficiency of runoff delivery to the outlet. Consistent with similar recent studies, the effect of logging on floods is controlled not only by the harvest rate but most importantly the physiographic characteristics of the watershed and the spatial distribution of the cutblocks. Imposed by the probabilistic framework to understanding and predicting the relation between extremes and their environmental controls, commonly used in the general sciences but not forest hydrology, it is the inherent nature of snowmelt-driven flood regimes which cause even modest increases in magnitude, especially in the upper tail of the distribution, to translate into surprisingly large changes in frequency. Contrary to conventional wisdom, harvesting influenced small, medium, and very large flood events, and the sensitivity to harvest increased with increasing flood event size and watershed area.
By C. Van Rensen, N.N. Neumann and V. Young (BC Ministry of Forests, Lands and Natural Resource Operations and Rural Development).
Introduction: The Government of British Columbia (the Province) is committed to sustainable resource management. As resource demands grow, we must be able to measure the combined effects of all resource development activities and natural disturbances, large and small, on the values important to the people of B.C. To meet this need, the Province established a Cumulative Effects Framework (CEF) in 2014 to guide the assessment of cumulative effects1 across natural resource sectors and support the integration of assessment results in natural resource decision-making. Application of the CEF is underway in the Kootenay Boundary Region, led by the Ministry of Forests, Lands, Natural Resource Operations and Rural Development. Through this initiative, the Elk Valley Cumulative Effects Assessment and Management Report was completed which included an assessment of Aquatic Ecosystems as a valued component, and led to identification of priority management and mitigation actions (Elk Valley Cumulative Effects Management Framework Working Group 2018). Since completion of the Elk Valley project, the Kootenay Boundary Cumulative Effects (CE) team has expanded their CE initiatives to other areas in the region. For the new initiatives a watershed assessment procedure first designated by Thompson Okanagan Region was adopted (Lewis et al. 2016). Regional modifications were made to the assessment methods and are presented in Van Rensen et al. (2020). These new assessment methods were first applied to the Kettle River drainage basin and results are presented in this report.
By Lisa Nordin
Since 2006, BC’s Forest and Range Evaluation Program (FREP) has sampled over 11,000 post-harvest sites to assesses the effectiveness of forest and range practices in conserving resource values, including riparian/streams and water quality. To date, the focus has been on random sampling at recently harvested cutblocks. Riparian/stream conditions are evaluated at a reach scale and results are typically summarized by natural resource district.
In 2019, a pilot project was completed in the Kootenay-Boundary region to develop and test a methodology for evaluating riparian/stream condition at a watershed scale using targeted sampling. This project was initiated in response to interest among decision makers in having information on factors influencing the condition of specific watersheds of concern. Using this methodology, FREP researchers combined reach-scale ground assessments in a pour-point sample design with GIS estimates of riparian disturbance to result in an integrated ranking of condition. Results were supplemented with data from assessments of potential sediment delivery and habitat connectivity at road crossings. Treatment and reference watersheds within the Kettle River and Kootenay Lake drainage areas were sampled, where the majority of land disturbances in the treatment watersheds were due to logging and roads, and the reference watersheds were mainly undisturbed by human development.
In the Kettle River drainage, the Boundary and Rock Creek treatment watersheds were found to be not properly functioning. The level of impairment was significantly higher in these two watersheds compared to all the others in the study, mainly due to a high amount of human-caused riparian disturbance. The reduced buffering capacity and resilience that results from an impaired riparian area means that these systems are presently in a sensitive state and may be easily affected and slow to recover from additional disturbance. Supplementary information gathered at road crossings indicates that sedimentation, livestock, and habitat connectivity for fish are also issues in the Boundary and Rock Creek watersheds. Attributes associated only with the stream channel identified flooding as one of the main causes of impacts in both treatment and reference watersheds in the Kettle River drainage, indicating that this area may be susceptible to naturally occurring high flow events.
In the Kootenay Lake drainage area, the Redfish treatment watershed was assessed to be in properly functioning condition, with results similar to several of the reference watersheds. Where indicators were impaired in Redfish, they were linked to road-related issues such as surface erosion and mass wasting using the riparian/stream evaluation. Similar issues were also observed at three road-crossing assessments in Redfish using the water quality assessment.
In addition to discussing the approach and findings, the report also presents recommendations for mitigating future detrimental effects in these watersheds.
WATERSHED ASSESSMENTS IN THE KOOTENAY-BOUNDARY REGION: Combining GIS and Ground-Based Methodology with Pour-Point Design (2020).pdf
By Sara A. Goeking and David G. Tarboton
Abstract: In coniferous western forests, recent widespread tree mortality provided opportunities to test the long-held theory that forest cover loss increases water yield. We reviewed 78 studies of hydrologic response to standing-replacing (severe wildfire, harvest) or nonstand-replacing (drought, insects, low-severity wildfire) disturbances, and reassessed the question: Does water yield or snowpack increase after forest disturbance? Collective results indicate that postdisturbance streamflow and snowpack may increase, not change, or even decrease, and illuminate factors that may help improve predictability of hydrologic response to disturbance. Contrary to the expectation that tree mortality reduces evapotranspiration, making more water available as runoff, postdisturbance evapotranspiration sometimes increased—particularly following nonstand-replacing disturbance—because of (a) increased evaporation resulting from higher subcanopy radiation, and (b) increased transpiration resulting from rapid postdisturbance growth. Postdisturbance hydrologic response depends on vegetation structure, climate, and topography, and new hypotheses continue to be formulated and tested in this rapidly evolving discipline.
Forests and Water Yield- A Synthesis of Disturbance Effects on Streamflow and Snowpack in Western Coniferous Forests (2020).pdf
By the Society of American Foresters
Position: The Society of American Foresters (SAF) supports policies, programs, and actions that enhance the health, sustainability, management, and restoration of forested watersheds. Healthy, resilient forests are essential to providing a clean and continuous supply of fresh water for humans and the environment. Forests also recharge aquifers, stabilize soils, filter pollutants, mitigate stormwater runoff, regulate stream flows, and moderate stream temperatures. SAF agrees that trees and forests are a critical component to solving the water-related challenges facing communities, utilities, businesses, and the environment, and that sustainable management is critical to improve the health and resilience of the nation’s watersheds.
Forest Water Resources A position of the Society of American Foresters (2020).pdf
By XuJian Joe Yu and Younes Alila
A common approach used by forest hydrologists to understand and quantify how forest harvesting affects floods was proclaimed flawed by a 2009 landmark study. With a century of forest hydrology research now questioned by academics and by governments alike, Yu and Alila were compelled to develop a new method, known as nonstationary frequency analysis, to evaluate continuous forest harvesting and regrowth effects on floods. The application of this method is demonstrated on the Greata Creek Camp paired watershed study site in the snow environment of British Columbia, Canada. The method reveals a highly sensitive flood regime to forest harvesting in a mid-elevation south-facing zone of the watershed, summarized as follows:
Tree removal increased the magnitude and frequency of floods across not only small and medium (return periods < 10-yr) but also the large events (return periods > 10-yr).
Floods can be sensitive to even small rates of forest harvesting, depending on location within the watershed. For instance, the removal of only 11% of the watershed’s trees doubled the frequency of floods of all sizes, as a result of a 9 –14% increase in the magnitude of such floods.
Depending on the extent of harvested area and the size of flood events, larger harvest or cut rates resulted in two, three, and fourfold increases in the frequency of large floods.
These outcomes run counter to the prevailing wisdom in hydrological science. The co-authors suggest that these outcomes have major implications for the safety of drainage structures such as bridges and dams, human settlements, drinking water quality, and the sustainability of riverine ecosystems. The co-authors call for a re-evaluation of past studies based on this new method.
For further information, contact Younes Alila at email@example.com
Read full study
By Rita Winkler and Sarah Boon
Introduction: Forest disturbance, whether natural or as a result of timber harvesting, directly affects stand-scale hydrologic processes through changes in interception, evaporation, and transpiration. When disturbance occurs over a large enough area, hydrogeomorphic processes at the watershed scale can also be affected. In British Columbia, statistically significant shifts in the timing and magnitude of snowmelt- dominated streamflows and in the frequency of peak flow events of all magnitudes have been measured in watersheds where more than 5% of the area has been clearcut. Streamflow regimes may also be affected following less extensive changes in forest cover where disturbance location and watershed attributes synchronize melt runoff timing and delivery to stream channels. These increases may have subsequent downstream effects on channel morphology, aquatic habitat, alluvial fans, floodplains, infrastructure, and community water supplies.
The potential effects of forest disturbance on streamflow are often evaluated by examining the total area disturbed and the location(s) in a watershed where forest cover has been (or will be) altered. The assumption is that the greater the disturbed area, the greater the potential for hydrologic change. It is also assumed that these changes will diminish over time as the forest regrows (i.e., recovers). The extent of disturbance, accounting for regrowth, is referred to as the equivalent clearcut area (eca). This note describes eca, including its origin, development, and use, how it is calculated, and its applicability to forest development planning and watershed assessment. This note focusses on eca in snow-dominated interior British Columbia watersheds where spring peak flows are a key hydrologic concern. However, the discussion applies wherever eca is used, although the methods of calculation and seasons considered may vary.
Equivalent Clearcut Area as an Indicator of Hydrologic Change in Snow- dominated Watersheds (2017).pdf
An investigation report by the BC Forest Practices Board (2016)
In February 2015, a local hunter and advocate for wildlife conservation submitted a complaint about Interfor Corporation’s (Interfor) cutblock 04Q-09 in Tree Farm Licence 8 (TFL 8). The cutblock is
20 kilometres north of Greenwood, in the Dry Creek watershed (see Figure 1). The complainant is concerned that the 454-hectare cutblock is too large and will negatively impact water and wildlife. He would like government to stop licensees from harvesting such large cutblocks.
There is a limit on cutblock size under the Forest and Range Practices Act (FRPA), but forest licensees are allowed to harvest larger cutblocks, subject to certain constraints. The effects of these larger cutblocks can be negative or beneficial, depending on the hydrology or species of wildlife present. Since the complainant raised concerns about the size of the cutblock at a general level, rather than about a specific wildlife species or hydrological effect, the Board investigated Interfor’s management of wildlife and water in the Dry Creek area by examining the following two questions:
Were Interfor’s management of water and assessment of hydrological risk reasonable?
Did Interfor adequately manage impacts to wildlife habitat and biodiversity at the stand level
and landscape level?
Forest licensees must comply with FRPA, but have discretion in how they address forest values that are not regulated. Each section of this report examines compliance with FRPA, followed by a discussion of how Interfor considered the risk of this large cutblock affecting water and wildlife values.
Dry Creek – Hydrology and Wildlife Concerns About a Large Cutblock FPB investigation report (2016).pdf
A graduating essay by Yu Chen submitted for a BSc at UBC.
Abstract: Stream sedimentation issues resulting from forestry practices are prevalent in the province of British Columbia. The impacts of riparian forest harvesting on the sediment regime of streams are of concern because of extensive commercial use of forest resources in BC. Forestry practices can alter the natural sediment balance and lead to abnormally high rates of sediment input resulting in increased concentrations of sediment in the water body and increased deposition of sediment on the stream bottom. The increase of sediment yield driven by forestry operations can reduce the storage capacity of reservoirs and degrade the water quality for human drinking, industrial, and recreational uses. Sediment inputs that exceed the background level and turbidity can also increase the risk to the survival and the integrity of aquatic ecosystems. Riparian forested areas in both coastal and interior plateau forest watersheds need careful considerations of riparian buffers and best management practices to avoid excessive sediment delivery into stream networks. Also, quantitative studies need to be conducted to compare different harvesting methods and provide forest management planner better suggestions to achieve both economic and environmental objectives. In general, a holistic approach is required to control sediment production across different landscapes. What’s more, a better understanding of the interaction between sediment dynamics and forest harvesting and continuous implementation of best management practices will result in fewer problems.
Assessment Of Effects Of forest Harvesting On Stream Sedimentation- A Focus On Coastal And Central Interior Forest Watersheds Of British Columbia (2016).pdf
By Oliver M. Brandes and Jon O'Riordan
Abstract: Water is society’s most critical and, increasingly, its most strategic asset. Without abundant clean and flowing fresh water—and functioning watersheds—there is no life, no economy, and no future. Yet, sustainable water use is increasingly under threat across the globe due to growing consumption, pollution, and rapid resource development, all of which impact watershed health and drinking water sources. The prospect of shifting hydrology due to a changing climate will only exacerbate the problems associated with these threats via, for example, more extreme weather events, increased flooding, and prolonged droughts.
Over the past 20 years, the Province of British Columbia has implemented a number of significant legislative changes to its resource management and governance regime. This will culminate in a new Water Sustainability Act, expected in 2014. As part of the Province’s recent Water Act modernization process, significant public discussion (instigated by government) has occurred around key aspects of water management and the extent to which water and related resource policy reforms are needed. Yet, the deeper and more complex dialogue about the who, how, what, and accountability of decision-making—the essence of watershed governance—is only just beginning.
Provincial and territorial governments across Canada are moving away from top-down, government-driven approaches and towards more collaborative and delegated forms of water and watershed governance. This mirrors trends in many jurisdictions around the globe. In Canada, Ontario, Quebec, parts of the prairies, and regions in the North are making changes to watershed governance based on meaningful engagement with affected communities, better involvement of First Nations, and improving financial support and capacity at the watershed level.
This Blueprint focuses on watershed governance in British Columbia and sets out a 10-year program for effectively managing and governing fresh water in the context of functioning and healthy watersheds. It represents a potentially transformative change for watershed governance in the province.
A Blueprint for Watershed Governance in British Columbia (2014).pdf
By Ryan J. MacDonald, Sarah Boon, James M. Byrne, Mike D. Robinson, and Joseph B. Rasmussen
Abstract: Native salmonids of western North America are subject to many environmental pressures, most notably the effects of introduced species and environmental degradation. To better understand how native salmonids on the eastern slopes of the Canadian Rocky Mountains may respond to future changes in climate, we applied a process-based approach to hydrologic and stream temperature modelling. This study demonstrates that stream thermal regimes in western Alberta, Canada, may only warm during the summer period, while colder thermal regimes during spring, fall, and winter could result from response to earlier onset of spring freshet. Model results of future climate impacts on hydrology and stream temperature are corroborated by an intercatchment comparison of stream temperature, air temperature, and hydrological conditions. Earlier fry emergence as a result of altered hydrological and thermal regimes may favour native westslope cutthroat trout (Oncorhynchus clarkii lewisii) in isolated headwater streams. Colder winter stream temperatures could result in longer incubation periods for native bull trout (Salvelinus confluentus) and limit threatened westslope cutthroat trout habitat.
Potential future climate effects on mountain hydrology, stream temperature, and native salmonid life history (2013).pdf
By Sarah Boon, Rita Winkler, John Pomeroy, and Dave Spittlehouse
Abstract: One of the most important ecosystem services from forested regions is the provision of a sustainable water supply. In the United States, for example, streamflow from forest land provides almost 2/3 of the total freshwater supply (Jones et al. 2009). On a global scale, forested headwaters that are snowmelt-dominated produce 60% of total runoff (Chang 2003). Given that forest ecosystems are significantly affected by climate change and associated forest disturbance such as wildfire, insect infestation, and disease (Westerling et al. 2006; Littell et al. 2009), there is a critical need to quantify the subsequent effect of these changes on water supply.
In British Columbia, the Forest and Range Practices Act (FRPA) requires the forest industry to incorporate non-timber values such as water into their forest management plans using best available knowledge. The response of snow processes to clearcut harvesting is well understood, and has been used as a forest management strategy to increase water yield from headwater basins (Hibbert 1967; Bethlalmy 1974; Ziemer et al. 1991; Wigmosta and Burges 2001). However, we know little about the effects of natural disturbance, such as mountain pine beetle (Dendroctonus ponderosae; MPB) and wildfire, and much of this more recent knowledge is at the stand rather than watershed scale (Winkler and Boon 2009; Bewley et al. 2010; Pugh and Small 2011; Schnorbus 2011). Our research expands previous stand-scale hydrologic process research to the source area watershed scale. The results provide forest and water resource professionals with key information required to assess the hydrologic consequences of forest response to climate change, and to make scientifically defensible water and timber management decisions.
Effects of climate and forest cover change on snowmelt dominated water supplies in the Okanagan (2012).pdf
By Rita Winkler, Dan Moore, Todd Redding, David Spittlehouse, Brian Smerdon and Darryl Carlyle-Moses
Abstract: The effects of forest disturbance on hydrologic pro- cesses and the generation of streamflow are highly variable and are influenced not only by the disturb- ance, but also by the weather and the biophysical characteristics, of the watershed. This chapter has described how forest harvesting and natural disturb- ance-related changes in fundamental hydrologic processes, including precipitation, interception, evaporation, and soil moisture, can influence hill- slope flow, groundwater, and streamflow. The details
the forest canopy account for some of the variability in hydrologic processes, such as snow accumulation and melt, among stands, but year-to-year differences in snowfall patterns account for the largest propor- tion of the variability (Winkler et al. 2005; Winkler and Moore 2006). Therefore, estimates of recovery derived from measurements made over a relatively small number of seasons may not adequately repre- sent the range of weather conditions expected within a given watershed, and at best, represent average conditions. The greatest uncertainty lies in the ap- plication of stand-scale recovery estimates and ECA indices to the evaluation of hydrologic change at the watershed scale. Linkages between stands, hillslopes, and entire watersheds are complex and vary with
the weather and the watershed; consequently, these linkages have not been quantified. A 50% recovery in snow accumulation or melt may not represent a 50% recovery in peak flow magnitudes. The ECA index provides only an indication of potential hydrologic change based on the extent of disturbance. It should not be used as a substitute for professional analyses and field assessments.
of past and ongoing research in British Columbia and elsewhere can be found in the references cited. New initiatives are building on this foundation by linking stand-scale processes to watershed response; by conducting modelling over greater temporal and spatial scales, with scenarios of extensive harvesting and changing climates; and by conducting field re- search to quantify the effects of natural disturbance on hydrology and hydrologic recovery.
The Effects Of Forest Disturbance On Hydrologic Processes And Watershed (2010).pdf