A spatially explicit network-based model for estimating stream temperature distribution

The WET-Temp (Watershed Evaluation Tool Temperature) model is designed to take advantage of spatially explicit datasets to predict stream temperature distribution. Datasets describing vegetation cover, stream network locations, elevation and stream discharge are utilized by WET-Temp to quantify geometric relationships between the sun, stream channel and riparian areas. These relationships are used to estimate the energy gained or lost by the stream via various heat flux processes (solar and longwave radiation, evaporation, convection and advection). The sum of these processes is expressed as a differential energy balance equation applied at discrete locations across the stream network. The model describes diurnal temperature dynamics at each of these locations and thus temperature distribution across the entire network. WET-Temp is calibrated to a tributary of the South Santiam River in western Oregon, McDowell Creek. The mean differences between measured and modeled values in McDowell Creek were 0.6°C for daily maximum temperature and 1.3°C for daily minimum temperature. The model was then used to predict maximum and minimum temperatures in an adjacent tributary, Hamilton Creek. The mean differences between modeled and measured values in this paired basin were 1.8°C for daily maximum temperatures and 1.4°C for daily minimum temperatures. Influences of model parameters on modeled temperature distributions are explored in a sensitivity analysis. The ability of WET-Temp to utilize spatially explicit datasets in estimating temperature distributions across stream networks advances the state of the art in modeling stream temperature

EFFICIENT PATTERNS OF CONSERVATION ACTIVITIES IN A WATERSHED: THE CASE OF THE GRANDE RONDE RIVER, OREGON

This research examines a spatially explicit allocation of habitat restoration activities in an Oregon watershed to meet water temperature targets for the benefit of endangered salmonid fish species. Integrating hydrological, biological and economic models, a series of optimization problems are investigated for different policy targets including temperature reductions and enhanced fish populations. Results indicated that the heterogeneous nature of riparian conditions and stream morphology needs to be considered if restoration activities are to be allocated efficiently in a watershed. We also found that it is less costly to implement restoration activities in tributaries if the objective is to maximize stream length where water temperatures decrease by a certain degree. Although temperature reductions are primarily achieved by shading in nearby reaches, if a desired level of temperature reductions increases, then it is necessary to apply restoration efforts in remote reaches.Resource /Energy Economics and Policy,

Drone-based Structure-from-Motion provides accurate forest canopy data to assess shading effects in river temperature models

Climatic warming will increase river temperature globally, with consequences for cold water-adapted organisms. In regions with low forest cover, elevated river temperature is often associated with a lack of bankside shading. Consequently, river managers have advocated riparian tree planting as a strategy to reduce temperature extremes. However, the effect of riparian shading on river temperature varies substantially between locations. Process-based models can elucidate the relative importance of woodland and other factors driving river temperature and thus improve understanding of spatial variability of the effect of shading, but characterising the spatial distribution and height of riparian tree cover necessary to parameterise these models remains a significant challenge. Here, we document a novel approach that combines Structure-from-Motion (SfM) photogrammetry acquired from a drone to characterise the riparian canopy with a process based temperature model (Heat Source) to simulate the effects of tree shading on river temperature. Our approach was applied in the Girnock Burn, a tributary of the Aberdeenshire Dee, Scotland. Results show that SfM approximates true canopy elevation with a good degree of accuracy (R2 = 0.96) and reveals notable spatial heterogeneity in shading. When these data were incorporated into a process-based temperature model, it was possible to simulate river temperatures with a similarly-high level of accuracy (RMS

An evaluation of different forest cover geospatial data for riparian shading and river temperature modelling

Riparian tree planting is increasingly being used as a strategy to shade river corridors and offset the impact of climate change on river temperature. Because the circumstances under which tree planting generates the greatest impact are still largely unknown, researchers are increasingly using process‐based models to simulate the impacts of tree planting (or felling) on river temperature. However, the high‐resolution data on existing riparian tree cover needed to parameterise these models can be difficult to obtain, especially in data‐sparse areas. In this paper, we compare the performance of a river temperature model parameterised with a range of different tree cover datasets, to assess whether tree cover data extracted from readily available GIS databases or coarser (i.e., 2–5 m) digital elevation products are able to generate river temperature simulations approaching the accuracy of higher resolution structure from motion (SfM) or LiDAR. Our results show that model performance for simulations incorporating these data is generally degraded in relation to LiDAR/SfM inputs and that tree cover data from “alternative” sources can lead to unexpected temperature model outcomes. We subsequently use our model to simulate the addition/removal of riparian tree cover from alongside the river channel. Simulations indicate that the vast majority of the “shading effect” is generated by tree cover within the 5‐m zone immediately adjacent to the river channel, a key finding with regards to developing efficient riparian tree planting strategies. These results further emphasise the importance of incorporating the highest possible resolution tree cover data when running tree planting/clearcutting scenario simulations

Modeling relative effects of riparian cover and groundwater inflow on stream temperature in lowland Whatcom County, Washington

Many Pacific Northwest streams have water temperatures that exceed thermal thresholds for salmonids. Supporting and maintaining streams with temperatures below these thermal thresholds requires an understanding of the relationships between the main factors influencing stream temperatures. This study examined the relative effects of two of these factors, riparian canopy cover and groundwater inflow, on stream temperatures at the reach scale. I measured stream temperature, net groundwater exchange, and riparian canopy cover levels in 10 different study reaches designed to comprise a factorial combination of reaches with vegetated and unvegetated riparian buffers, as well as gaining and not-gaining groundwater. I then modeled stream temperatures in each reach with the SSTEMP stream temperature model, and compared model-predicted temperatures to measured stream temperatures during the warmest part of the summer. Finally, I manipulated the model to examine the relative impacts of riparian canopy cover (0-100%) and groundwater inflow (0-50%) on predicted stream temperatures. SSTEMP predicted daily mean reach temperatures well across the range of conditions studied here, although it overpredicted daily maximum temperatures. Model manipulations of groundwater inflow and canopy cover levels showed consistent trends in affecting stream temperatures. Under peak summer conditions and base groundwater (0%) and canopy cover (0%) conditions, predicted mean stream v temperatures warmed by an average of ~ 4°C across all streams. Full canopy cover and 50% groundwater inflow each reduced this predicted warming by ~ 2.5°C when manipulated independently. However, only the combination of both high canopy cover and groundwater inflow actually reduced predicted mean stream temperatures within the study reaches. In contrast, canopy cover had much stronger effects on modeled maximum stream temperatures than did groundwater inflow. Under peak summer conditions, 100% canopy cover reduced predicted downstream warming of daily maxima by ~ 10°C, while 50% groundwater inflow did so by only ~ 2°C compared to base conditions. The results of this study affirm that both canopy cover and groundwater inflow play significant roles in minimizing stream temperatures in summer, and both should be considered when making restoration, land use, and other management decisions

Heat balance of alcoves on the Willamette River, Oregon

Alcoves in some river systems are cooler than the mainstem of the river and provide thermal refugia for aquatic species. An energy balance and sensitivity analysis on 3 alcoves in the Willamette River, Oregon indicate that alcove size and alcove flux determine the degree to which meteorological conditions affect the alcove water temperature. Large alcoves with a low alcove flux and large surface area are more sensitive to meteorological conditions (i.e., shade and wind). Small alcoves with a high alcove flux and small surface area are more sensitive to the temperature of emerging subsurface water than to meteorological conditions. The temperature of hyporheic water relative to the mainstem is determined by its residence time; longer flow paths disperse the diurnal signal and move hyporheic water into equilibrium with mean seasonal or annual subsurface temperatures. Floodplain restoration may increase alcove population in a river system thereby making it a potential credit trading tool for mitigating excess thermal loading in a heat stressed river.Keywords: alcoves, cold water refugia, hyporheic flow, energy balanc

The Shade Credit Incentive Landscapes of the McKenzie/Willamette Confluence

Increasing population and land use decisions have had a negative effect on the aquatic ecosystems in the Willamette River Basin. One result is elevated temperatures in many of the Basin’s streams, which adversely affect the fish that live in these streams. There are several regulatory mechanisms in place to improve water quality; however, recent attention has been focused on market-based pollution credit trading systems as an alternative approach. Clean Water Services, the public water utility in the Tualatin Watershed near Portland recently began the first program in the country to trade temperature pollution credits for creating shade. This project explores the distribution of high and low shade credit potential in the landscape around the confluence of the Willamette and McKenzie Rivers using the peer reviewed WET_Temp stream temperature model. The intent of this project is to provide a tool for land use planners to explore the geographic characteristics of high incentive areas (high shade potential) and target these areas with shade credit programs. Also, this project explores the effects of management decisions on the changing shade credit incentive landscape.Keywords: water quality trading, stream temperature, Clean Water Services, Willamette Basin TMD

Stream temperature drivers and modelling in headwater catchments on the eastern slopes of the Canadian Rocky Mountains

xi, 110 leaves: illustrations (some coloured), maps ; 29 cmThis thesis quantified processes controlling stream temperature using a field study conducted in headwater catchments on the eastern slopes of the Canadian Rocky Mountains, Alberta. Hydrometeorological data from May-September of 2010 and 2011 were used to describe the drivers of inter-annual stream temperature variation in Star Creek. Inter-annual stream temperature variation was shown to be a function of catchment-scale moisture conditions, driven by seasonal differences in snow accumulation. This field study demonstrated that meteorological and hydrological processes must be considered simultaneously in order to understand stream temperature response to changing environmental conditions in mountain regions. A process-based modelling approach was developed to simulate stream temperature in Star Creek using hydrometeorological and geomorphological data collected during the field study. Modelling results suggest simulations of hydrometeorological variables needed for process-based stream temperature modelling are possible in data-sparse mountain regions using little input data. Model calibration was required because not all variables required for calculating the stream energy budget were measured. However, stream energy budget estimates did compare well with other estimates from field-based studies, providing confidence in the methods applied. A sensitivity analysis demonstrated that simulations were most sensitive to net radiation and parameterization/calibration of surface-subsurface interactions. Results from a climate change study presented in Chapter 4 suggest winter habitat for native salmonids may be reduced as a function of changes in the onset of spring snowmelt. Chapter 4 results suggest that bull trout (Salvelinus confluentus) populations are likely more sensitive to climate change than isolated westslope cutthroat trout (Oncorhynchus clarki lewisii) populations. The climate change study was limited due to boundary conditions remaining constant for all simulations and modelling error. However, these results are supported by an inter-catchment comparison of air temperature, stream temperature, and stream discharge between Lynx, Lyons East and Star creeks. The inter-catchment comparison and climate change results present a conceptual framework of thermal response to climate change that has not been discussed in the literature. Overall, this thesis demonstrates that catchment- and regionally-specific conditions must be considered when assessing the potential impacts of environmental change on stream temperature and native salmonids