مرکزی صفحہ River Research and Applications Economic analysis of water temperature reduction practices in a large river floodplain: an...
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RIVER RESEARCH AND APPLICATIONS River. Res. Applic. 24: 941–959 (2008) Published online 1 April 2008 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/rra.1112 ECONOMIC ANALYSIS OF WATER TEMPERATURE REDUCTION PRACTICES IN A LARGE RIVER FLOODPLAIN: AN EXPLORATORY STUDY OF THE WILLAMETTE RIVER, OREGONy SAICHON SEEDANG,a*,z ALEXANDER G. FERNALD,bx RICHARD M. ADAMS cô and DIXON H. LANDERS dk a b d Institute of Water Research, Michigan State University, Room 101A Manly Miles Building, 1405 S. Harrison Road, East Lansing, MI 48823-5243, USA Department of Animal and Ranges Sciences, New Mexico State University, Box 30003 MSC3-I, New Mexico State University, Las Cruces, NM 88003, USA c Department of Agricultural and Resource Economics, Oregon State University, 200A Ballard Extension Hall, Corvallis, OR 97331-3601, USA U.S. Environmental Protection Agency, National Health and Environmental Effects Research Laboratory, Western Ecology Division, 200 SW 35th Street, Corvallis, OR 97333, USA ABSTRACT This paper examines ecosystem restoration practices that focus on water temperature reductions in the upper mainstem Willamette River, Oregon, for the benefit of endangered salmonids and other native cold-water species. The analysis integrates hydrologic, natural science and economic models to determine the cost-effectiveness of alternative water temperature reduction strategies. A temperature model is used to simulate the effects of combinations of upstream riparian shading and flow augmentations on downstream water temperatures. Costs associated with these strategies are estimated and consist of the opportunity costs of lost agricultural production and recreation opportunities due to flow releases from an up-stream reservoir. Temperature reductions from another strategy, hyporheic flow enhancement, are also examined. Restoration strategies associated with enhanced hyporheic cooling consist of removal/reconnection of current obstacles to the creation of dynamic river channel complexity. The observed red; uction of summer water temperatures associated with enhanced channel complexity indicates that restoring hyporheic flow processes is more likely to achieve cost-effective temperature reductions and meet the total maximum daily load (TMDL) target than conventional approaches that rely on increased riparian shading or/and combinations of flow augmentation. Although the costs associated with the hyporheic flow enhancement approach are substantial, the effects of such a long-term ecological improvement of the floodplain are expected to assist the recovery of salmonid populations and provide ancillary benefits to society. Copyright # 2008 John Wiley & Sons, Ltd. key words: water temperature models; hyporheic temperature; cost-effectiveness analysis; Willamette River; floodplain restoration; economic analysis Received 21 December 2007; Accepted 7 January 2008 INTRODUCTION Over 70% of Oregon’s population lives in the Willamette River basin, and three-quarters of Oregon’s economic output is derived from activities in the basin (Willamette Restoration Initiative, 2001). However, after 150 years of human use and proximity to the river, there are signs of declines in the state of ecological health in the region. These symptoms include changes in the diversity of river and floodplain landscapes, a recent degradation of river water *Correspondence to: Saichon Seedang, Institute of Water Research, Michigan State University, Room 101A Manly Miles Building, 1405 S. Harrison Road, East Lansing, MI 48823-5243, USA. E-mail: email@example.com y This manuscript has been subjected to the United States Environmental Protection Agency peer review process, and modified with permission from the American Society of Civil Engineers (ASCE). z Environmental Scientist. x Associate Professor. ô Professor. k Senior Scientist. Copyright # 2008 John Wiley & Sons, Ltd. 942 S. SEEDANG ET AL. quality after several decades of improvement, a widespread increase of invasive plants and animal species and the disappearance and decline of many native plants and animal species (Willamette Restoration Initiative, 2001). Among these changes, an important public policy concern in the basin and in the Pacific Northwest region is the decline of native salmonid fish species (National Research Council, 1996; National Marine Fisheries Service, 1999). Salmon have played an important economic, cultural and religious role in the Pacific Northwest for centuries. These factors have motivated local, state and federal agencies as well as private organizations, to set restoration goals for the Willamette River and other watersheds for the benefit of salmon and other species. Numerous restoration plans have been proposed by public agencies and private organizations (e.g. the Pacific Northwest Ecosystem Research Consortium (PNW-ERC), Oregon Biodiversity Partnership, Oregon Wetlands Joint Venture, Willamette Valley Livability Forum and the state of Oregon). Several proposed habitat restoration strategies include restoring main and side river channels, dam removal, replanting riparian forest and reducing in-steam water temperature. However, few studies have attempted to measure the biological and economic tradeoffs within the mix of activities and resources to be used in each management plan. The lack of comprehensive, systematic assessments of proposed plans is due in part to the complexity of modelling important physical and ecological processes, and in estimating the possible outcomes associated with manipulations to such systems. In addition, analyses of the cost-effectiveness of proposed restoration plans have generally not been integrated into current efforts. Another area of management interest that has not been addressed in current assessments is the potential role of hyporheic flow enhancement1 in the suite of possible techniques to reduce in-stream water temperatures. The research reported here provides an exploratory assessment of the cost-effectiveness of alternative strategies, including the potential for hyporheic process enhancement, to reduce temperatures in a large river system. The overall objective of this research is to conduct an economic analysis of alternative restoration practices to address excessively high water temperature in a large dynamic river floodplain system. Specifically, economic and biophysical information will be used to assess the efficiency of various restoration plans associated with compliance of in-stream temperature targets needed to restore salmonid populations. Information on restoration costs of each strategy, the resulting ecological benefits (temperature reductions to enhance ‘aquatic life use’ as required by Clean Water Act (Copeland, 1999)), and the physical and economic tradeoffs between proposed strategies are needed to provide guidance when considering investments in ecosystem restoration and management of a large river. The upper mainstem Willamette River is selected as the empirical focus for the study because prior work indicates that this is an appropriate location for the proposals explored here (Gregory et al., 1998; Dykaar and Wigington, 2000; Fernald et al., 2000). Water temperature is selected as the key parameter to determine the effectiveness of the restoration approaches. This is motivated by current regulatory interest (i.e. Oregon Total Maximum Daily Loads (TMDLs) development, Oregon Water Temperature Standard) and availability of water temperature models to perform such a management analysis. BACKGROUND The mainstem Willamette River flows northward for 299 km through a large alluvial floodplain of the Willamette Valley before entering the Columbia River near Portland (Altman et al., 1997). The upper river, the primary focus of this research, has a higher gradient with a wide floodplain, and it is characterized as a complex system of meandering and braided channels containing numerous side channels and islands (PNW-ERC, 2002). Mean annual flow on the mainstem (measured at the Albany USGS Gauge 14174000) is approximately 400 m3 s1 (Dykaar and Wigington, 2000). Most of the flow in the Willamette River occurs from November to March as a result of winter 1 There is increasing recognition of hyporheic flow influencing water quality and other ecological functions, specifically in an alluvial river landscape (Landers et al., 2000, 2002; Ward et al., 2002). Hyporheic flow is a relatively new area of research. As a result, its definition often changes with each researcher’s focus, the physical characteristics of the study site and the methodology of the study. This research follows the definition of hyporheic flow by Fernald et al. (2000, 2001 and 2006) as it relates to the Willamette River. Specifically, hyporheic flow is river water flowing along a gradient and passing through various channel features (e.g. alcoves, bars, islands). During summer, a mixing of surface and subsurface water flows beneath these features and results in temperature cooling in micro-habitats (e.g. alcoves, side channels) and the main river channel. Greater channel complexity results in increased hyporheic flow and a substantial cooling effect which may considerably influence overall river water temperature. Copyright # 2008 John Wiley & Sons, Ltd. River. Res. Applic. 24: 941–959 (2008) DOI: 10.1002/rra WATER TEMPERATURE REDUCTION PRACTICES 943 rain and spring snowmelt. About 35% of the annual runoff is from snowmelt, either directly into the stream or indirectly through the ground-water system (Laenen and Bencala, 2001). Summer and fall low-flow periods are significantly affected by federally managed reservoir operations, which have historically been managed for flood control and summer low-flow augmentation since the 1970s. As a result of low-flow augmentation, the amount of water supplied to the main channel during the summer months is elevated over previous uncontrolled flows (PNW-ERC, 2002). Unfortunately, there are no historical temperature data bases for the upper main channel of the Willamette that are of acceptable quality to reconstruct historic, pre-dam temperature characteristics in the river during summer low flow. However, the known reduction of complexity and connectivity that has resulted in about an 80% loss of total channel complexity (PNW-ERC, 2002) has, undoubtedly, resulted in major temperature alterations. The primary alteration is the loss in the quality and quantity of cold refugia that were derived from the historic off-channel habitat cooled by hyporheic connectivity and shaded by extensive gallery forests. Moreover, the loss of in-stream large wood has resulted in fewer cool scour holes associated with root wads. Currently, summer water temperatures in the entire mainstem Willamette River exceed the state water temperature standard, and the river is listed as ‘water temperature limited’ under the 2002-303(d) list. The primary purpose of the temperature standard is to protect fish.2 Most salmonids in the basin, including Chinook salmon (Oncorhynchus tshawytscha) and steelhead trout (Oncorhynchus mykiss), spawn in the tributaries of the Willamette River and use the mainstem river for rearing and migration habitats (Altman et al., 1997). The decline of many native fishes in the Willamette River has been widely recognized and reported. The primary causes are the decline of water quality, including a change in temperature patterns, the decline of total channel length as a result of bank revetment and disconnection of main channel to side channels and the loss of riparian shade, structure and diversity, especially in urban and agricultural areas (Benner and Sedell, 1997; Willamette Restoration Initiative, 2001). In addition, Willamette anadromous salmonids face the same ocean and migratory problems confronting other stocks of salmonids in the Northwest, such as ocean conditions, harvest rates and other impediments to migration, and pollution. These external conditions are beyond the scope of this study. A number of studies have observed and modelled how stream water temperature is influenced by various factors including human influences such as land use practices, destruction or removal of riparian vegetation and flow diversion and dam operations (Beschta et al., 1987; Bartholow, 1991; Hostetler, 1991; Isaak and Hubert, 2001). Knowledge about stream water temperature responses to these physical and biophysical changes can be linked to develop and evaluate potential management practices. Hyporheic flow restoration is another potential approach in addressing problems related to water temperature. In a large floodplain, water temperature reduction resulting from hyporheic flow processes can be promoted by expanding the extent (i.e. connectivity and complexity) of river channel characteristics (Boulton et al., 1998; Fernald et al., 2000). For example, the removal of constructed erosion protection structures (i.e. rip-rap) along a river that tend to reduce channel complexity and diversity should be considered a crucial restoration practice. Efforts to reconnect channels to the floodplain can also be promoted, especially in the potentially active reaches that are currently not extensively used for societal and economic purposes (Gregory et al., 1998). Reconnecting a river with its channel and floodplain may improve hyporheic flow temperature and water quality, but also could result in retention and storage of water (which results in reduced magnitude of peak flows), sustained base flow and increased habitat complexity (Coulton et al., 1996; Boulton et al., 1997). An important policy consideration when making decisions related to habitat restoration is determining which strategies are most effective in meeting the restoration target at the lowest cost. There is a need to integrate economic information and biophysical complexity of habitat ecosystems with restoration management practices. Examples of efforts to link the complexity of the habitat ecosystem with economic information of management decisions can be found in several studies. For example, Kuby et al. (2005) use basin level optimization models to evaluate tradeoffs between ecological benefits and economics cost of dam removal in the Willamette basin. Paulsen and Wernstedt (1995), Hickey and Diaz (1999) and Stevens et al. (2002) applied economic concepts to the design of 2 In the mainstem Willamette River, the 7-day average maximum water temperature criterion is 17.88C (648F), except in the lower portion of the river (the first 50 miles from the river’s confluence with the Columbia River), where the standard is 208C (688F) (Oregon Department of Environmental Quality, 2003). Copyright # 2008 John Wiley & Sons, Ltd. River. Res. Applic. 24: 941–959 (2008) DOI: 10.1002/rra 944 S. SEEDANG ET AL. environmental management policies involving complex physical and natural resource information and applied optimization techniques to select management methods that attained the desired objective (e.g. a minimum stream flow requirement) at the least cost. Johnson and Adams (1988) studied the economic benefits of flow levels on steelhead populations in the John Day River, Oregon. They quantified the benefits of increased fish numbers to anglers under various water allocations by combining a fish production model with an on-site economic valuation analysis. Adams et al. (1993) later developed a bio-economic model for riverine management in the John Day River. The model was used to develop a cost-benefit analysis comparing the efficiency of management actions in terms of improved fish production and habitat. Several studies have investigated investments in habitat conservation programmes in terms of their efficient allocation of funds (e.g. Wu and Boggess, 1999; Wu et al., 2000; Wu and Skelton-Groth, 2002; Watanabe et al., 2005). These studies found that an efficient allocation of funds must consider the cumulative effects and environmental benefits, which depend on the threshold effects of conservation efforts of targeted restoration sites. The conditions investigated by these studies involve traditional riparian habitat investments (e.g. reestablishing riparian corridors) to reduce water temperature for anadromous fishes in streams and tributaries in small watersheds. The research described here differs in that it investigates and compares investments in various restoration practices to reduce water temperature in a large river floodplain. The results from this research, while exploratory, provide information on selecting appropriate restoration investments suited to sites characterized as large river floodplains. PROCEDURES AND METHODOLOGY Restoration practices Three general categories of management practices that can be implemented in the study area to reduce water temperature include: (1) increasing riparian shade by planting trees along the main channel; (2) flow augmentation via releases of cooler water from upstream reservoirs and (3) restoring/recreating channel complexity to promote hyporheic flow functions. Riparian planting is considered a key restoration strategy for any ecological approach which aims to improve fish habitat and water quality in the Northwest (Kauffman et al., 1997). Active restoration strategies, such as planting riparian buffer zones with native plant species along the upper mainstem Willamette River, may recover some of ecological functions that have been lost over time primarily due to agricultural conversion. In particular, shading of the steam surface has the potential to reduce stream temperatures by reducing the incidence of solar radiation. The value of foregone agricultural production and the costs of establishing such riparian vegetation buffer zones are the primary costs of this practice. Stream temperatures can also be cooled by deep-water releases from reservoirs in the upper portion of the basin, given that hypolimnetic water released from reservoirs is substantially cooler than incipient stream temperatures. Costs of this practice include lost recreational opportunities in the reservoirs (due to accelerated drawdown), and the lost value of the water for alternative uses. Reconnection of the floodplain to the main channel to create more complex fish habitats and promote fluviohydro-geomorphic processes that contribute to hyporheic cooling is another potential restoration management practice (Landers et al., 2002; Fernald et al., 2006). Over the past century, placement of rock boulders or revetments (i.e. rip-rap) to protect farmland and property from erosion has created obstacles to the natural maintenance and creation of fluvial hydro-geomorphic processes (e.g. erosion and sedimentation). Removal of some of this bank protection would promote the ecological connection of river and floodplain. However, the quality of floodplain soil is particularly well suited for high valued agricultural uses, such as orchards, nursery stock and other specialty crops. As a result, any proposal to allow some of these farmlands to revert to more natural riparian state will require compensation for lost production from such highly valued agricultural land. The effectiveness of restoration practices Two models are used to measure the effects of the selected management activities on water temperature reduction in the study area. The first model is the CE-QUAL-W2 water temperature, which is used to measure the Copyright # 2008 John Wiley & Sons, Ltd. River. Res. Applic. 24: 941–959 (2008) DOI: 10.1002/rra WATER TEMPERATURE REDUCTION PRACTICES 945 response of water temperature to a change in riparian shading and tributary inflow into the upper mainstem Willamette River. The second model is a hyporheic flow temperature model, used to determine water temperature change associated with an increase in channel complexity. CE-QUAL-W2 water temperature model. The CE-QUAL-W2 is a two-dimensional longitudinal/vertical (laterally averaged), hydrodynamic water quality model. The model predicts water surface elevations, velocities and temperatures as well as other water quality variables. A recent version of this model (Version 3.1) incorporates the slope of river sections, and has the capacity to model the entire river basin with features such as dams, rivers and lakes (basin simulation). The model incorporates the effects of both vegetative and topographic shading in a stream channel. Vegetation characteristics represented in the CE-QUAL-W2 model are tree top elevation, distance of tree from the river centreline and tree density. The algorithm of the CE-QUAL-W2 model uses the position of the sun to determine which topographic inclination angles coincides with the direction of incoming solar radiation. Eighteen directions around each model segment are defined in this model (Annear et al., 2001). This Willamette temperature model has been calibrated to ensure appropriateness of all model components and applicability by the research team at Portland State University (PSU) and the model has been used for developing TMDL management programmes of the Oregon Department of Environmental Quality in the entire mainstem and most of its major tributaries. The calibration model-data error statistics for the mainstem Willamette River indicate that the model performs well in terms of temperature predictions. For example, the maximum daily water temperature calibration error statistic at all 12 calibrated stations has an absolute mean error (AME) of less than 18C for temperature predictions (Annear et al., 2003a). At the Corvallis observation station used in this research (downstream of the upper mainstem river), the AME value is within 0.358C of the observed data.3 The model reach of the upper mainstem Willamette River used for this study, approximately 92 km, is shown in Figure 1. Downstream water temperature north of Corvallis was selected as the reference site to investigate the temperature responses to upstream management scenarios. The CE-QUAL-W2 model was used to predict the response of water temperature to various scenarios of riparian shading on the upper section of the mainstem Willamette River and tributary flow increases from Cougar reservoir (a U.S. Army Corps of Engineers reservoir) via the McKenzie River. Simulated water temperatures from each management scenario were exported to Excel spreadsheets to calculate a 7-day moving average of daily maximum temperatures. These were compared with the state water temperature standard throughout the summer from June through the end of September, the period of the year when elevated water temperature is of greatest concern. Hyporheic flow model. In addition to the CE-QUAL-W2 water temperature model that includes riparian planting and tributary inflow management, another temperature model is needed to investigate the effects of management practices that promote hyporheic flow functions. While the study of hyporheic flow effects on temperature is a relatively new research area, there is recent research on hyporheic flows in the Willamette River that is relevant to this study (Fernald et al., 2000, 2001, 2006). Fernald et al. examine the relationship of hyporheic water temperature and dynamic channel features and show that hyporheic water temperature is closely associated with hyporheic flow in that surface water cools as it flows through various channel features (e.g. side channels, islands, sand bars, channel bed and banks), reemerges, and mixes with surface water downstream. The result of this mixing decreases the ambient main channel surface water temperature. Current understanding indicates that the extent of cooling depends on several factors, including hydraulic gradients, flow volumes, area and type of channel features and vegetation types. We further explored these relationships and estimated hyporheic cooling, and interpolated the results to policy analysis of restored channel complexity. Hyporheic cooling was estimated along a 67 km reach of the Willamette River using a hydrometric estimate of total hyporheic flow amount, an empirically based function for hyporheic cooling; and a mixing model to estimate river cooling from hyporheic flow. Hyporheic cooling is most likely in summer when river water is relatively warmer. Concurrent temperature measurements of hyporheic flow and main channel flow at a site near Corvallis, 3 The CE-QUAL-W2 model application to the mainstem Willamette River was calibrated by Professor Scott Wells and the Water Quality Research Group at Portland State University. The results of model calibration using 2001 and 2002 data produce similar statistical results (Berger et al., 2003, pages 143 and 151). For the detailed discussion of model calibration or validation/verification in the context of the water quality model, CE-QUAL-W2, see pages 23 to 25 of Cole and Wells (2007). Additional publications and applications related to this model can be found in Berger et al., 2002, Annear et al., 2003b, Wells et al., 2004, Rounds, 2007. Copyright # 2008 John Wiley & Sons, Ltd. River. Res. Applic. 24: 941–959 (2008) DOI: 10.1002/rra 946 S. SEEDANG ET AL. Figure 1. Upper Willamette River model study. Note: The upper reach of the mainstem Willamette River is selected to investigate water temperature responses under various management scenarios. Spatially, the length of the upper mainstem Willamette River model for this study is approximately 92 km. The model starts from south of Eugene (near the confluence of the Middle Fork and Coast Fork Willamette) to north of Corvallis. The model simulation used here was from 5 June 2001 to 30 September 2001. The Water Quality Research Group at Portland State University provided assistance in separating this model from the main model for this reach of the Willamette River, as well as calibrating the model for this research. This figure is available in colour online at www.interscience.wiley.com/journal/rra Oregon, showed hyporheic water was cooler than main channel water from late May until early September, after which hyporheic water was warmer than main channel water. An annual combined surface and subsurface heat budget might show a net balance for hyporheic temperature effects. The focus in this study is on hyporheic cooling that occurs in the critical period of June through August when river temperatures are high and most prone to exceedance of regulatory standards for fish tolerance. Bed form interacting with flow velocity affects stream-bed hyporheic exchange with rapid residence times in shallow depths into the stream bed (Cardenas and Wilson, 2007). Channel morphology also affects surface–subsurface exchange, with high flux and short residence times within the upper meter of the stream bed (Cardenas et al., 2004). Our method focuses on head gradient-driven hyporheic flow and cooling that takes place over long hyporheic flow paths. River features conducive to hyporheic flow, where hydraulic gradients conduct water into the river bed and banks, were identified with 1998 aerial photos based on 1997–1999 field studies (Fernald et al., 2001, 2006). A GIS coverage (Figure 2) was generated with three types of features: (1) islands in their entirety; (2) peninsulas separated from the river bank by a line 308 off thalweg flow direction, representing the typical subsurface flow path from river Copyright # 2008 John Wiley & Sons, Ltd. River. Res. Applic. 24: 941–959 (2008) DOI: 10.1002/rra WATER TEMPERATURE REDUCTION PRACTICES 947 Figure 2. Example island, peninsula and point bar hyporheic flow features of the Willamette River study area, with lines denoting crosssectional width, WH, for each feature. This figure is available in colour online at www.interscience.wiley.com/journal/rra to alcove head and (3) meander bends with less than 1000 m radius of curvature and within 80 m of the river bank, where hyporheic residence times are expected to be short enough that subsurface water exhibits hyporheic characteristics. Vegetated and bare gravel areas of each feature were distinguished in separate GIS coverages. Hyporheic flow volume was calculated for each feature with Darcy’s law (Hubbert, 1969). Feature crosssectional width, WH (m), was digitized perpendicular to the hyporheic flow direction (Figure 2). Feature flow depth multiplied by WH gave mean cross-sectional hyporheic flow area, AH (m2). Flow depth for peninsulas was set equal to alcove depth derived from a function relating peninsula length to alcove depth based on bathymetry data from 16 representative alcoves (Landers et al., unpublished data). Peninsula flow depth ranged from 0.7 to 2.0 m. Based on our field studies of hyporheic flow paths, we assigned representative flow depths of 2.0 m for meander bends and 4.0 m for islands. Feature mean hyporheic flow path length, LH (m), was calculated as feature surface area divided by WH. Hyporheic hydraulic gradient (DH/DL) was LH divided by the change in elevation over LH. The change in elevation was calculated using distance travelled along the shoreline of each feature multiplied by 0.001, the representative river water slope. We used surface cover as a surrogate for saturated hydraulic conductivity, Ksat (m s1), based on the previous peninsula deposit study (Fernald et al., 2006) and dye tracer studies (Fernald et al., 2001). Vegetated areas had lower Ksat (0.04 m s1), and bare gravel areas had higher Ksat (0.37 m s1). Single feature total hyporheic flow, QH (m3 s1), was equal to Ksat AH DH/DL. River cooling was calculated with QH and individual feature hyporheic cooling, DTH (8C). A function of cooling per metre of hyporheic flow path length was developed using LH and previous study hyporheic temperature data (Fernald et al., 2006). Temperature data were from two periods, July and August 1999, and from six sites representative of the range of Ksat from low (vegetated) to high (bare gravel) sites. For all features, DTH ¼ 30.08 þ 32.28 EXP (0.001757 LH). To determine the hyporheic-cooling effect on river water temperature, DTR (8C), we used a simple percentage dilution calculation with hyporheic flow, QH, and river flow, Q (m3 s1): DTH (QH/Q) ¼ DTR. We tabulated DTR from each hyporheic flow feature and summed the change in cooling from each feature to determine cumulative river cooling. We identified 149 island, peninsula and meander bend features over 67 km of the Willamette River from river km 278 to 211. Median feature area was 9680 m2, with all areas totalling 4.26 km2. Median QH of 0.061 m3 s1 resulted from median DH/DL of 0.002, median AH of 120 m2 and median Ksat of 0.26 m s1. Median feature hyporheic cooling, DTH, of 2.78C resulted in a river temperature change, DTR, of 0.618C over the study reach. Copyright # 2008 John Wiley & Sons, Ltd. River. Res. Applic. 24: 941–959 (2008) DOI: 10.1002/rra 948 S. SEEDANG ET AL. We feel this is a conservative estimate of hyporheic cooling and represents the lower end of expected hyporheic cooling of river water for a few reasons. We used conservative approaches in developing relationships, as shown in the following three examples. First, alcove depth as an index of peninsula hyporheic flow depth may underestimate hyporheic inflows that begin deeper in the river and arrive in the alcoves. Second, we used a median hyporheic flow path length for alcoves, treating the peninsula features as triangles. However, in one case we looked at in detail, the flow paths are longer than the median value and would result in more cooling than we calculated. Third, our gradient estimates were conservative, being based on a calculation of shoreline distance that in one case resulted in a hyporheic gradient less that the river gradient where we know there is actually a steeper gradient through the feature than around the feature. Importantly, we only considered deposit features visible from aerial photos. Field observations revealed at least 12 major riffle complexes associated with river channel thalweg gradient breaks over the 30 upstream river km of the 67 river km we analysed. Photo analysis suggested about the same number on the downstream 37 km. There is surely an important amount of hyporheic flow through riffles and other features that create hydraulic gradients into the river bed. The cooling functions of large river riffle complexes have not been fully described (as far as we know) and are an important area for future research. For scenario evaluation in the economic analysis, we employed results of previous studies to estimate possible cooling effects of all hyporheic flow paths. Dye tracer studies suggested 70% of river flow passed through hyporheic flow paths over the study reach (Fernald et al., 2001). Median hyporheic cooling of 2.78C for this amount of total hyporheic flow would result in river cooling of 1.98C. Though we did not have direct field measurements of the cooling associated with all hyporheic flow paths, this estimate may approximate the upper end of expected hyporheic cooling. An average cooling of 1.38C for these two estimation methods, [(0.61 þ 1.9)/2], is used as a baseline for existing hyporheic cooling associated with an area of hyporheic features before channel restoration in the study area. In predicting the cooling effects after channel restoration, we used channel surface area as an indicator and assumed that when an area of channel surface increases, the channel complexity, the area of hyporheic features and the degree of hyporheic cooling downstream will also increase proportionately. This assumption is a very conservative estimation because the cooling effect from hyporheic flow after channel restoration could be more significant due to a longer hyporheic flow path and larger areas of hyporheic interaction in river floodplain. It should be noted that there are several factors that affect hyporheic flow and its cooling ability, including flow magnitudes and their orientation to the features, channel and feature dimensions, and type of substrates and that further study is needed. The estimation of channel surface area before and after channel restoration (i.e. removing, breaching or reengineering revetments and reconnecting old side channels) is obtained from the Pacific Northwest Ecosystem Research Consortium (PNW-ERC, 2002).4 According to the PNW-ERC Conservation 2050 Scenario, it is estimated that after restoration (year 2050), the total channel surface area of alcoves and side channels would increase almost 160% relative to 1995 conditions. This percentage is used as a reference to interpolate the area of hyporheic features which determine the potential area for hyporheic cooling. Restoration costs Estimates of the costs of each restoration action are needed for a comprehensive evaluation of the cost-effectiveness of resources used in these management practices. These costs should include both the direct implementation costs and the economic opportunity costs. Direct costs are associated with costs for design, construction, operation, maintenance and monitoring of a restoration activity. Opportunity costs refer to a benefit forgone due to implementation of a management practice (e.g. the agricultural benefits lost if farmland is taken out of production). Major restoration costs associated with management practices include riparian planting, land purchase, bank revetment removal and lost recreation opportunities in upriver reservoirs. Costs that involve multiple time periods (i.e. 4 The PNW-ERC developed three alternative future plans for the Willamette River Basin. These plans range from greater emphasis on conservation to greater emphasis on economic development. The ‘Conservation Scenario 2050’ focuses on land and water allocation for conservation and restoration of ecological functions, which includes reconnecting the river channel and removing and/or modifying some revetments of meander bends of the mainstem Willamette River. Copyright # 2008 John Wiley & Sons, Ltd. River. Res. Applic. 24: 941–959 (2008) DOI: 10.1002/rra WATER TEMPERATURE REDUCTION PRACTICES 949 maintenance and operation in support of the riparian shading approach) are adjusted to reflect present value dollar amounts in order to make comparisons among management options of various time lengths.5 Riparian planting costs include site preparation, materials (trees), labour and operational costs. Planting costs are associated with the first year of project implementation as well as the operational costs that occur over the life of the project. Planting costs are based on a standard cost per unit for Oregon (estimated by the U.S. Department of Agriculture, Natural Resource Conservation Service (NRCS) for the 2003 fiscal year). The average cost of planting riparian trees per river kilometre (15 m width) for both sides of the river channels is estimated at $11 250 (or $3000 per acre). The total consists of two major costs, site preparation and planting (trees and labour costs). Other site-specific costs (e.g. replacement due to first year tree mortality, fencing, tree shelter, irrigation water, stream bank stabilization, etc.) are likely to vary by site and are not included in this analysis. Riparian planting costs estimated from several other sites in Oregon (e.g. Grande Ronde River; Tualatin River and Beaver Creek) show substantial variation because of the differing site characteristics and practices implemented (types of trees, methods of planting and spacing). The estimated costs per river kilometer from these sites ranged from $7500 to $20 625 (Knoder, 1995; Bishaw et al., 2002; Watanabe, 2003). The costs used here fall within the general range observed at these other sites. It should be noted that riparian planting is not included in the hyporheic-cooling analysis of this study, given that riparian planting may actually reduce channel migration rates (Micheli et al., 2004). In fact, as a result of dynamic geomorphologic process, riparian vegetation development will occur naturally over time. Another component of major costs associated with riparian shade and hyporheic flow enhancement practices is the cost of land. Land prices from market transactions should reflect the discounted value of agricultural production that could be derived from this land over time. However, obtaining market price information of farmland that is not affected by other factors in the Willamette Valley, such as urbanization pressures, is difficult. In addition, the sale price for riparian farmland exclusively is not available. Fortunately, the estimated real market value (RMV) is available for all counties in the study area.6 Therefore, this research uses RMV estimates to represent opportunity costs of taking agricultural land out of production. Estimated market values (i.e. RMV values) and land-use zoning information are provided through Geographical Information System (GIS) or digital data formats obtained for the three counties within the study area (Linn, Benton and Lane Counties). The average market value of farmland within 100 m of the upper mainstem Willamette River is approximately $4600 per acre. Within the study area, the average market value is highest in Benton County and lowest in Linn County. This average market value of farmland, especially in Benton County, is comparable with the actual sale prices of several parcels of farmland in 2002 (personal communication with Toni Blessing, Appraiser, Benton County, 2003). The average land value is used to represent the cost of land that would need to be acquired for restoration approaches (i.e. planting trees to achieve shading or for reconnecting the river to its floodplain to achieve enhanced hyporheic cooling). In addition to the cost of purchasing land, the hyporheic-cooling practice also include the average costs of removing rock rip-rap placed along the banks to protect farmland from erosion. The USACE District Office in Portland estimated an average cost of $10 per cubic yard ($13 per cubic metre) for revetment removal (personal communication with Mike McAleer, the U.S. Army Corps of Engineers, Portland District, December 2006). The cost estimate is based only on the removal of rock material. Other site-specific costs, such as the costs of bank slope stabilization after removal of rip-rap, material disposal, transportation, access roads and permit acquisition are not included. To determine the locations and lengths of revetment to be removed, we utilized data from the ‘Conservation Scenario 2050’ of the PNW-ERC that estimated the length of required revetment on the upper Willamette for removal to be 2716 m, or about 5% of the upper river total bank length. This proposed restoration also estimated the acreage of land needed for restoring floodplain natural processes in the next 50 years to be about 890 acres.7 5 All relevant costs are discounted to reflect the net present value with a 5.875% discounting rate, as used by the National Resource Conservation Services (NRCS) and other federal agencies during the period of 2002–2003(Department of the Interior, 2002). 6 RMV is the estimated price for which property would sell in a transaction at the assessment date for the tax year. RMV is estimated by county assessors based on several criteria, such as a comparison of sale prices from similar properties and/or physical inspection (ORS 308.205). 7 The excel spreadsheet, as well as other information related to this estimate, was obtained directly from Linda Ashkenas, Oregon State University, Fisheries and Wildlife Department. Copyright # 2008 John Wiley & Sons, Ltd. River. Res. Applic. 24: 941–959 (2008) DOI: 10.1002/rra 950 S. SEEDANG ET AL. Another important component of costs associated with restoration practices is the opportunity cost of releasing upstream reservoir storage. One of these costs is the reduced flatwater recreation opportunities at those reservoirs which are drawn down as a result of increases in streamflow. Although there are other uses for the water stored in the McKenzie River reservoirs, the opportunity costs are judged to be low and are not included in this analysis.8 The data used to estimate lost recreational benefits are primarily drawn from the Willamette Basin Recreation Study Report.9 Other sources of data for estimating recreational values (e.g. reservoir water level, volume, surface area and recreational visitation data) were obtained from the U.S. Army Corps of Engineers, Portland District. The procedures employed to calculate recreation benefits consist of three steps (see details in Seedang, 2004): (1) reservoir water levels under flow management scenarios were calculated using regression analysis linking reservoir elevation, area capacity (acres) and flow release; (2) the effect of reservoir water levels on recreation visitations was estimated using a coefficient on the water level variable in the visitation model employed in the Willamette Basin Recreation Study Report and (3) the reservoir recreation benefits were estimated by multiplying the change in visitations (estimated from step 2) with the marginal visitation recreation benefit. Visitation recreation benefits (i.e. the willingness to pay or marginal benefit of an individual recreationist making an additional trip to visit the reservoir), for Cougar reservoir were estimated by the USACE in the Willamette Basin Recreation Study Report. The recreation benefits due to changes in reservoir water level reflect the opportunity costs of recreation benefits forgone for the 2001 water year from releasing additional reservoir water to downstream. The result showed that on average, the value of reservoir recreation impact during summer (June–September) is $2.75 per acre-foot of water released downstream (the highest impact is in September at $ 3.4 per acre-foot). This estimated value is low when compared with other reservoir recreation studies (e.g. recreation values for releases from California Central Valley reservoirs ranged from $6 to more than $600 per acre-foot (Ward et al., 1996)). This lower value for Willamette Valley reservoirs may be due to a variety of reasons, such as the presence of alternative recreation sites and opportunities within the upper basin (e.g. Blue River Lake, McKenzie River), or specific reservoir characteristics such as shallow bank slopes, which result in less impact on recreation activities from reservoir drawdown. Selection of cost-effective strategies The final step in the evaluation procedure is to combine the information and methods into a decision-making framework. Specifically, once the responses of water temperature and the costs associated with each proposed restoration practice is determined, various restoration options can be compared. A cost-effectiveness analysis is then used to determine the least cost option that achieves a given level of temperature reduction or ecosystem function target. A cost-effectiveness frontier for these options can also be constructed with these targets. The cost-effectiveness frontier represents the least cost envelope of points for restoration options that achieve various levels of temperature reduction. In cost-effectiveness analysis, the preferred alternative is the one that produces the socially desirable temperature reduction at minimum cost. Simulation results of water temperature reduction scenarios from riparian shading, flow augmentation and their combinations (total of 25 scenarios) from the CE-QUAL-W2 water temperature model are used for evaluating and constructing the cost-effectiveness frontier. 8 We used only lost recreational opportunities as the opportunity costs of increased stream flows because the other uses of these storage reservoirs (flood control, hydropower and irrigation) are unlikely to be affected by the releases for increased streamflows during August and September. Specifically, there is very limited agricultural use (approximately 1600 ac-ft) of these stored waters. Total hydropower generated will not change as a result of changes in release patterns, only the KWH rate may vary. However, shifts from one month to the next in this generation are not likely to result in a significant change in revenues generated. Finally, flood control is provided by drawing down the storage reservoirs in the fall to create storage for winter and spring flows. Releases of additional stream flows in August would not change the storage capacity of the reservoirs available in the winter. Should these assumptions change, the costs of the flow augmentation strategy may be underestimated. 9 The Willamette Recreation Study Report is part of the U.S. Army Corps of Engineers Portland District’s (USACE) Willamette Basin Reservoir Feasibility Study Project. In this report, the operations of the 13 dams of USACE are evaluated to consider the effects of changes in water demand. Copyright # 2008 John Wiley & Sons, Ltd. River. Res. Applic. 24: 941–959 (2008) DOI: 10.1002/rra WATER TEMPERATURE REDUCTION PRACTICES 951 RESULTS AND DISCUSSION Base case scenario The base case model simulates a situation where no restoration effort takes place. The downstream profile shows that summer water temperatures (on the basis of a 7-day moving average of daily maximum temperatures) during the simulated period (5 June–30 September 2001) violated the state water temperature standard more than 75% of the time, with most of these violations occurring during the months of July and August. Moreover, for 25% of the summer period, the water temperature exceeded 208C (Figure 3). It is expected that such persistent high water temperatures during these periods will cause stress to several cold-water fish species, especially salmonids rearing in this area (Altman et al., 1997). The longitudinal profile of simulated water temperatures for the base case at several locations is also examined. Water temperatures at all locations are higher than the Oregon state standard (17.88C). The general profile of water temperature is an increase in temperature as it flows downstream. However, in some locations, such as the middle section of the river, there is a major cooling effect from the tributary and possible hyporheic processes. Several dye-tracer studies (i.e. Fernald et al., 2001; Laenen and Bencala, 2001) performed on this part of the river showed significant existence of hyporheic flow. Maximum temperature reduction from riparian shading and flow augmentation The simulation results from the maximum riparian shade scenario show limited water temperature reductions (average of less than 18C) at the downstream observation reach. In addition, water temperature on most days in July and August exceeds the TMDL standard (Figure 4). Several factors limit the effectiveness of riparian shade in reducing water temperature in the Willamette. One factor is the inability of tree height to provide adequate shading for the river surface area exposed to solar energy. Given the broad nature of the mainstem river channel, and the north–south orientation, the ability of riparian trees to provide shadows across the entire channel is limited. Also, as the volume of the main stem river flow is relatively large, it is difficult for cumulative riparian shade to have a substantial effect on water temperatures over a long length of the river. Cumulative cooling effect from shade may have a significant effect on water temperature at the local scale or at the site immediately downstream due to a shorter travel-time of flow before getting exposed to the daily heat. Rounds (2007) used the same model to evaluate Figure 3. Comparison of simulated water temperatures for the base case scenario with water temperature standard 17.88C (State of Oregon Water Temperature Standard). Note: The State of Oregon has designated the upper mainstem Willamette River as an area for salmonid rearing and migration. No activity is permitted that will raise the water temperature of the receiving water body if the receiving water body already exceeds 17.88C on the basis of a 7-day moving average of daily maximum temperature. The ODEQ uses this information in developing the TMDL for water temperature for the upper mainstem Willamette River. This figure is available in colour online at www.interscience.wiley.com/ journal/rra Copyright # 2008 John Wiley & Sons, Ltd. River. Res. Applic. 24: 941–959 (2008) DOI: 10.1002/rra 952 S. SEEDANG ET AL. Figure 4. Comparison of water temperature reduction scenarios during the summer months with the base case. Note: Water temperatures reported here are the 7-day moving average maximum daily temperatures. Base case scenario is the simulated existing condition of water temperature during the summer of 2001; maximum riparian shade scenario is based on full riparian shade for the entire 92 km with maximum tree height; and maximum riparian shade with flow increments (þ50%) is the combination of the maximum riparian shade and the additional flow (þ50%) increments from the McKenzie River upstream tributary of the mainstem Willamette River. This figure is available in colour online at www.interscience.wiley.com/journal/rra shading effects on selected-5 mile reaches of the mainstem Willamette and found significant local effect on water temperature, while there is little cooling effect of temperature over the entire length of the river. The analysis of the effects of increased water volume in the upper mainstem Willamette River indicates that augmented flow from the McKenzie River also has limited impact on temperatures. We found cooling effects of flow augmentations (þ25 and þ50%) to be around 0.25–0.488C. Rounds (2007) also found overall cooling effects in the mainstem Willamette River were in the similar ranges of our study and the effects of cooling were further diminished downstream. In our study, even when we combined flow augmentations with maximum riparian shade efforts, downstream water temperature is not reduced sufficiently to meet the state water temperature standard for the months of July and August. Specifically, the average summer water temperature can only be reduced by approximately 18C or about 5% from the base case scenario. However, even a reduction of this magnitude is still biologically important to salmonid rearing and migration habitats (Hostetler, 1991; Altman et al., 1997). Cost-effectiveness results from riparian shading and flow augmentation scenarios A total of 25 management scenarios (including existing condition or no investment) were simulated to investigate the effectiveness of their impacts on water temperatures. The scenarios are sets of combinations of riparian shading on the upper mainstem Willamette River (which is further divided into three segments; upper, middle and lower sections, to investigate the differences of temperature responses). The scenarios also consider flow augmentation practices (which also considered the temperature responses between releasing flow during the hottest months (July and August) compared to the entire summer (July to September)). Costs (in present values) corresponding to the per cent of temperature reduction of the 25 management scenarios are plotted against their effective temperature reduction (from the base case) to construct a cost-effectiveness frontier. Results show that only 10 of the 25 scenarios are cost-effective solutions for a given budget and a desired level of temperature reduction (Figure 5). The other 15 scenarios result in less cooling for the same or higher expenditures. The results show that to achieve small temperature reductions, increasing reservoir releases in July and August alone are cost-effective. However, as the target level temperature reduction increases, riparian shade combined with increased flow is required. Within the combinations of riparian shade and flow increases, the cost-effectiveness of each point begins with planting riparian for shading on the upper sections of the mainstem river and moves towards Copyright # 2008 John Wiley & Sons, Ltd. River. Res. Applic. 24: 941–959 (2008) DOI: 10.1002/rra WATER TEMPERATURE REDUCTION PRACTICES 953 Figure 5. Selected scenarios on the cost-effectiveness frontier. Total cost per scenario reported here is in present value terms, and maximum temperature reduction in each scenario is calculated as the percentage difference from the base case. Note: e0, base case (no management) with existing riparian shade; e23, existing riparian shade plus tributary flow increments (þ25%) in July and August; d20, existing riparian shade plus tributary flow increments (þ50%) in July and August; d18, full riparian shade only upstream plus tributary flow increments (þ25%) in July and August; c14, full riparian shade only upstream plus tributary flow increments (þ50%) in July and August; b10, full riparian shade only upstream plus tributary flow increments (þ50%) in summer (June, July, August, September); b8, full riparian shade only downstream plus tributary flow increments (þ50%) in summer (June, July, August, September); a5, full riparian shade upstream and downstream plus tributary flow increments (þ50%) in July and August; a2, full riparian shade upstream and downstream plus tributary flow increments (þ50%) in summer (June, July, August, September); a1, full riparian shade on all sections of the river (upstream, middle stream and downstream sections) plus tributary flow increments (þ50%) in summer (June, July, August, September). This figure is available in colour online at www.interscience.wiley. com/journal/rra additional planting on the lower sections as greater cooling is required. Importantly, note that the scenarios of riparian planting for shade alone are more costly than flow augmentation. The total cost of selected scenarios as mapped on the cost-effectiveness frontier range from no cost for no management effort, to a total cost of almost $3 million when combining incremental flow augmentation (þ50%) and maximum riparian shade for the entire 92 km associated with a 5% reduction of water temperature (18C temperature reduction) from the base case. Note that since this analysis is not premised on maximization of total benefits (or benefit-cost analysis), there is no single optimal or ‘best’ solution in terms of investments in temperature reduction practices, and we are only searching for least costs ways to obtain a temperature reduction. The solutions shown are based on their costeffectiveness, and can therefore be useful in selecting least cost alternatives. Hyporheic-cooling effects and costs The results from the first set of management options indicate that neither riparian planting for shading, nor flow augmentation, or any combination of both, can reduce water temperatures in the study area to a level that meets the current Oregon standard. This suggests that improving water quality and fish habitats in large rivers with active floodplains like the Willamette will need a broader suite of management approaches, including enhancement of hyporheic flow functions. This section examines temperature reductions and costs as a result of manipulating hyporheic flows through increasing channel complexity. Table I summarizes the results of estimated hyporheic cooling associated with existing channel features and predicted temperature reductions following 50 years of channel restoration. We estimated that there would be a maximum net reduction of 1.998C from 1995 conditions due to the increase in channel complexity as a result of restoration activities (through the year 2050). Copyright # 2008 John Wiley & Sons, Ltd. River. Res. Applic. 24: 941–959 (2008) DOI: 10.1002/rra 954 S. SEEDANG ET AL. Table I. Predicted hyporheic cooling associated with channel complexity Description Total channel surface area (km2) Hyporheic feature area (km2) Cooling effect (8C) Before restoration After restoration Net change 13.6 4.3y 1.3z 35.2 11.1 3.3 21.6 6.8 2.0x Based on GIS data of the Willamette River in 1995 and a 50-year estimation by the PNW-ERC. Total channel surface area includes main channel, sloughs and side channels. y Based on GIS coverage of active channel from 1996 to 1998 by Fernald et al. (2006). The hyporheic features include mid-channel bars, point bars and islands. z Based on an average cooling from two estimation methods (see details in Procedures And Methodology section). x Assuming that when an area of channel surface increases, the area of hyporheic features, and the degree of hyporheic cooling downstream, will increase by the same proportion. Estimated costs of restoring channel complexity are based on the PNW-ERC future scenarios (Conservation 2050 Scenario).10 In this research, we focus only on the promotion of hyporheic cooling arising from increased channel complexity. As a result, the major costs of this approach are land purchases to allow for channel migration, and the removal of rip-rap. We estimate that the total costs for a net reduction of 1.998C of this approach is $4.3 million and the average cost of water temperature reduction by this approach is approximately $2.15 million per 18C reduction. The majority of the costs for this approach is from the cost for purchasing land (about 95% of total cost). Several important points regarding these results and associated costs of channel restoration should be noted. First, this hyporheic approach does not include the costs of any other restoration activity, such as riparian planting. However, even if riparian buffers are not planted, natural reforestation of the riparian landscape will occur over time.11 Second, it is uncertain that implementation of a riparian forest buffer is even necessary or desirable after removal of some rock revetments from the side channels. Since the nature of channel complexity restoration requires the dynamic processes of erosion and sedimentation, combined with lateral movement of the main river channel to recreate the hyporheic channel features, replanting riparian forest in some areas (unstable reaches) may be subject to removal due to future erosion (Dykaar and Wigington, 2000; Landers et al., 2000). This in itself is not a negative occurrence since trees deposited in the river create channel complexity by contributing ‘large wood’ to the river system. Moreover, the sediment eroded into the river has the potential of contributing to hyporheic cooling by being deposited downstream. Therefore, including all costs of forest buffer reestablishment with implementation of this approach likely overstates the costs of this plan. In addition, since the majority of channel features associated with hyporheic cooling are in the area near the main channel, cost per degree of hyporheic cooling estimated here may be over estimated. Third, a restoration approach that focuses on increased hyporheic features as well as riparian establishment (i.e. cottonwood colonization), would not be successful without considering restoration of some historical flow regimes which have been altered since the construction of upstream dams. Thus, flow management, such as increases in the frequency and magnitude of flows (e.g. high flow or bank full discharge) is desirable and would increase the rate of restoration of channel complexity and connectivity (Dykaar and Wigington, 2000; Landers et al., 2000). Restoration of some aspect of historical flow regimes for the Willamette River is mechanically a relatively straightforward and inexpensive activity due to the various dams and control structures located on the tributaries that feed into the upper river. The operation of these dams is under the jurisdiction of the U. S. Army Corps of Engineers and they are currently (January 2007) considering operating the dams to re-establish ‘environmental 10 As suggested by the PNW-ERC team, the restoration processes involved are located near both sides of the mainstem, side channels are planting with riparian buffers, some bank revetments are removed and some old side channels are reconnected to the main channel. 11 Based on tree ages we have collected, mature riparian forests (10 m high) can be established via natural seeding in 15 to 35 years or an average of 25 years (Steve Cline, unpublished manuscript). There is the issue of a ‘reset’ period where a newly established gravel bar may experience a period of dynamic equilibrium (frequent disturbance) that prevents establishment of what will become mature riparian forests. This has been included in to the above estimate. Copyright # 2008 John Wiley & Sons, Ltd. River. Res. Applic. 24: 941–959 (2008) DOI: 10.1002/rra Copyright # 2008 John Wiley & Sons, Ltd. Reestablishment of maximum riparian forest on both sides of the main channel (a buffer width of 15 m) An increase of flow from a reservoir on the McKenzie River during summer months (June to September) Removal of some bank revetments and restoration of historical channels to increase the interaction between surface and subsurface water and promote channel complexity Riparian shadingy Costs for removal of bank revetment and costs of purchasing lands for channel migration, including potential loss of land near the river to erosion Reservoir recreation benefit loss from drawdown during summer months Costs of purchasing lands and costs of planting Cost component 1.99 (9.5) 0.48 (2.5) 0.63 (3.3) Maximum temperature reduction from the base case, 8C (%) 4.28 0.64 2.68 Total cost (millions) 2.15 1.33 4.25 Average cost per degree of reduction (millions) All costs are measured as net present value. The majority of costs for the riparian planting approach are assumed to occur within the first year of the project. The recreation costs for the flow augmentation are estimated as an annual cost. All costs for the hyporheic-cooling approach are assumed to occur within the first year. y This approach assumes shading will provide maximum temperature reduction at a tree height of 35 m, beginning after 10 years of growth and planting activities are within the first year of project to ensure that shading is maximized within 50 years. z Flow augmentation involves increments to mainstem flows through upper reservoir releases during the summer months using two levels of flow increments (þ25% and þ50%). x This approach is assumed to provide maximum effectiveness in temperature reduction within 50 years. It is also assumed that the restoration activities occur within the first year, so that it will take 50 years of sufficient channel complexity to realize the full temperature reduction. Hyporheic coolingx Flow augmentationz Description Approach Table II. Descriptions, cost components, assumption notes and cost estimations for each restoration approach WATER TEMPERATURE REDUCTION PRACTICES 955 River. Res. Applic. 24: 941–959 (2008) DOI: 10.1002/rra 956 S. SEEDANG ET AL. flows’ that contribute towards restoration of historic ecosystem services, such as providing more habitat and cooler temperatures for threatened and endangered native fish species. There would be little additional cost associated with improving environmental flows in this fashion. For fish habitat to be significantly improved, it is not necessary to cool the entire river system. By increasing the overall temperature heterogeneity in the upper Willamette River through restoring habitat and hyporheic cooling opportunities, fish would be able to find cool temperature refugia more easily and use these refuges during periods of maximal thermal stress. Finally, the most difficult aspect of river restoration is not the science or economics—both of which appear to be favourable, but the societal aspect of getting a diverse group of landowners to appreciate the societal importance of creating this ‘Green Infrastructure’ and its documented ecological and societal benefits. Moreover, these landowners (mostly family owned farms) can supply products potentially as valuable, if not more so, to society as the actual crops they are currently producing. These new products would be ecosystem services such as aquatic habitat, terrestrial habitat, water quality and flood protection. Currently, efforts to establish market incentives, such as Oregon’s Willamette Partnership, are developing an innovative ‘ecosystem market-based’ approach designed to improve water quality in the Willamette River basin. This programme encourages landowners to implement ecosystem restoration and conservation practices such as planting trees or restoring floodplains to reduce stream temperatures and they would be able to trade (sell) their ‘credits’ to other regulated discharge activities (e.g. wastewater and storm water discharges from municipalities and industries). Cost estimation for each approach and its potential maximum temperature reduction is summarized in Table II along with their descriptions and assumptions. The riparian shading approach has the highest cost per degree of cooling because it has only a small impact on water temperature, and riparian establishment costs occur at the beginning of the project. An increase in tributary flows is the least costly approach; however, it has limited potential for temperature reduction (0.488C), given the small amount of water available in the tributary for such a purpose during the low-flow summer months. The average cost of a hyporheic-cooling approach is based on an investment plan that needs to be finished within the first year of the plan, in order to realize the full temperature reduction within 50 years. CONCLUSIONS AND FURTHER RESEARCH Economic and ecological information is needed to assess the cost-effectiveness of various practices when developing restoration policies to improve water quality and fish habitat. In addition, restoration approaches need to be adjusted to the specific environmental settings of the area of interest when designing a suite of appropriate restoration practices for salmonids. Water temperature is one of the most important habitat qualities that influence cold-water fishes like salmonids. Flow augmentation and riparian shading are considered practical ecological restoration practices designed to reduce water temperature. These conventional practices have worked well in reducing temperatures in many small rivers and tributaries; however, they appear to be incapable of lowering water temperatures in a large floodplain river such as the Willamette, where efforts of flow augmentation have proven ineffective and the river itself is too large to provide effective shading. An alternate restoration practice that focuses on floodplain restoration to promote hyporheic cooling may provide a more effective reduction of water temperatures in the upper Willamette River, which has experienced loss of heterogeneity and cool microsites. Promoting heterogeneity and hyporheic cooling may be the only feasible approach to provide locations of cool water in this reach of the river. The benefit of restoring channel complexity and/or connectivity of river and flood plain is not only for cooling, but it also provides habitat heterogeneity for fish and other wildlife. Though the costs of this approach are difficult to estimate and may appear high, there are other unintended economic benefits, including reduction of flood damage (by reducing the amount of agriculture in the lowest floodplains and by allowing storage and conveyance on floodplains), reduced maintenance costs (not maintaining rip-rap and levees), improved aesthetics, increased aquatic and terrestrial habitat diversity and recreational opportunities. This research provides an initial starting point in terms of evaluating alternative management approaches for investment in water temperature reduction in a large river floodplain. However, these results need to be conditioned by several features of the analysis. First, the hyporheic-cooling alternative may prove a viable alternative for restoration management, especially when a resource manager wishes to achieve a relatively large temperature Copyright # 2008 John Wiley & Sons, Ltd. River. Res. Applic. 24: 941–959 (2008) DOI: 10.1002/rra WATER TEMPERATURE REDUCTION PRACTICES 957 reduction target. However, given the many interpolations involved in the estimation of hyporheic cooling reported here, use of these results should be limited to exploring the potential for alternate restoration policies. Before specific policies are implemented, additional quantitative analyses of the relationships between hyporheic cooling, channel complexity and other variables related to temperature reduction are needed. Second, as with the derivation of ecological outcomes, the economic information developed here is subject to uncertainty arising from the data and assumptions. For example, some site-specific costs are not included in the restoration activities and only one opportunity cost (recreation) is assigned to the flow augmentation strategy. While these may cause an underestimate in costs per unit of cooling, this potential bias may be offset by the potentially greater degree of cooling from hyporheic flow increases than was used in this study. Third, water temperature reduction is not the only benefit of ecological restoration. Other benefits exist, especially those associated with restoration of riparian forest and river floodplain habitat (i.e. source of food supply for wildlife species, habitat diversity, increased habitat area, bank stabilization, etc.). An accounting of these associated benefits, in combination with temperature reduction targets, needs to be part of any exercise in selecting an appropriate restoration approach. Accounting for these other TMDL and environmental targets will reduce the net costs per unit of temperature reduction by explicitly valuing associated non-target benefits. Given current interest in tradable permit systems for TMDL’s in Oregon and elsewhere, questions such as how one denominates these ecosystem services (temperature reduction and other targets) in units that can be traded, needs attention. Finally, while cost-effectiveness may be helpful in determining the best policy when facing specific budget constraints, it does not provide either the optimal biological or economic solution (i.e. situations where the net benefits to society of restoration are maximized). To move towards maximization of net benefits, development of a fish population model associated with water temperature and other environmental factors is needed. In addition, quantification of the value of fish benefits into monetary values must be done if the goal is to complete a benefit-cost analysis. ACKNOWLEDGEMENTS The authors are thankful to Dr Scott Wells, Dr Robert Annear and Mr Mikel McKillip at Portland State University for their assistance with the CE-QUAL-W2 water temperature model application to the mainstem Willamette River; Linda Ashkenas and the Pacific Northwest Research Consortium for helping provide the complete GIS data for the Willamette Basin; Mike McAleer and the engineering team from the U.S. Army Corps of Engineers, Portland District for providing data on revetment removal costs and the Willamette reservoir study; Dr JunJie Wu, Department of Agricultural and Resource Economics, and Dr Stephen Lancaster, Department of Geosciences, at Oregon State University for their support and providing guidance for this research. This research is partially funded through financial support from the Department of Agricultural and Resource Economics at Oregon State University. REFERENCES Adams RM, Berrens R, Cerda A, Li H, Klingeman P. 1993. 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