RIVER RESEARCH AND APPLICATIONS
River Res. Applic. 30: 40–44 (2014) Published online 24 January 2013 in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/rra.2642
MODELLING CHANGES IN SALMON HABITAT ASSOCIATED WITH RIVER CHANNEL RESTORATION AND FLOW-INDUCED CHANNEL ALTERATIONS† M. GARD* U.S. Fish and Wildlife Service, Sacramento, CA 95825, USA
ABSTRACT The River2D two-dimensional hydraulic and habitat model was used to simulate fall-run Chinook salmon (Oncorhynchus tschawytscha) spawning and fry and juvenile rearing habitat of the first phase of a stream channel restoration project on Clear Creek, California. Habitat was simulated for a range of stream flows: (1) before restoration; (2) based on the restoration design; (3) immediately after restoration; and (4) after one and two large flow events. Hydraulic and structural data were collected for three sites before restoration, and prerestoration habitat was simulated. Habitat simulated for these sites was extrapolated to the prerestoration area based on habitat mapping. The topographical plan for the restoration was used to simulate the anticipated habitat after restoration. Although the restoration increased spawning habitat, it was less successful for rearing habitat. Channel changes associated with high-flow events did not entirely negate the benefits of the restoration project. The results of this study point out the need for models that can simulate the changes in channel topography associated with high-flow events, which could then be used to simulate habitat over time. Published 2013. This article is a U.S. Government work and is in the public domain in the USA. key words: river restoration; habitat enhancement; adaptive management; fall-run Chinook salmon (Oncorhynchus tschawytscha); validation of habitat predictions Received 1 May 2012; Revised 11 December 2012; Accepted 20 December 2012
INTRODUCTION In response to the worldwide decline in freshwater fish (Dudgeon et al., 2006), substantial resources have been invested in restoring fish habitat (Shields et al., 2003; Bernhardt et al., 2005). Hydraulic and habitat models have been used to design and evaluate the success of river restoration projects (Pasternack et al., 2004; Wheaton et al., 2004a, 2004b; Gard, 2006) as an application of adaptive management (Walters, 1986). Implicit in the design, but not yet modellable, is how the amount of habitat created by the restoration projects will change over time in response to alterations in the channel topography caused by high flows. If restoration projects are not sustainable, the investment in restoration will be for naught. The objective of this article is to quantify how restoration and flow-induced channel changes altered weighted useable area (WUA) for fall-run Chinook salmon (Oncorhynchus tschawytscha) spawning and fry and juvenile rearing using the River2D hydraulic and habitat model (Steffler and Blackburn, 2001). I hypothesized that: (1) the restoration project would result in an increase in WUA, and (2) an index of habitat quality called the combined suitability index *Correspondence to: M. Gard, U.S. Fish and Wildlife Service, 2800 Cottage Way, Room W-2605, Sacramento, CA 95825, USA. E-mail:
[email protected] † The findings and conclusions in this article are those of the author and do not necessarily represent the views of the U.S. Fish and Wildlife Service.
(CSI) would be higher for occupied locations (where redds were present) than for unoccupied locations. The latter hypothesis serves as a biological validation of the habitat predictions. I did not have an a priori hypothesis of what effect high flows would have on the sustainability of habitat created by the restoration project. WUA is computed as the product of the CSI and the area associated with nodes of the River2D computation mesh, summed over the entire site.
METHODS Clear Creek, in the Central Valley of California, has a mean annual flow of 7.4 m3/s. The restoration project consists of the construction of a new sinuous channel with alternating riffles and pools in a 3.1-km reach of Clear Creek (122 250 3900 N, 40 290 5000 W). Historic gravel mining had resulted in channel incisement to the point that underlying bedrock was exposed in a large portion of the riverbed. This study was conducted for the first 350-m-long in-channel phase of restoration, constructed in 2002 and hereafter referred to as 3A. Significant changes to the topography of 3A after restoration occurred as a result of peak flows of 101.7 m3/s on 30 April 2003 and 69.1 m3/s on 17 February 2004. Fall-run Chinook salmon spawning and fry (< 60 mm SL) and juvenile (> 60 mm SL) rearing WUA were modelled: (1) before restoration; (2) based on the restoration design; (3) immediately postrestoration (2002);
Published 2013. This article is a U.S. Government work and is in the public domain in the USA.
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and (4) after one (2003) and two (2004) large flow-induced channel changes. For prerestoration modelling of 3A, three sites were selected from the 3.1-km restoration reach. These, taken together, included all habitat types present in 3A prior to restoration. Specifically, the three sites together had three runs, one riffle, four glides, three pools, four backwater units and two side channel runs. All of 3A after restoration was modelled. Details on data collection for the prerestoration sites are given in Gard (2006). The entire length of 3A prior to restoration was habitat-typed by field observations. The habitat typing data were used to extrapolate the results of the modelling to all of 3A prior to restoration. Habitat types consisted of pools, runs, riffles and glides. Pools were characterized by the presence of a downstream hydraulic control; riffles were characterized by shallow (< 0.5 m), fast (> 0.5 m/s) conditions; runs were characterized by deeper conditions with surface turbulence; and glides were classified based on having a glassy water surface. Details on the hydraulic modelling of the prerestoration sites and the plan for the restoration project are given in Gard (2006). All of 3A after restoration was modelled using data collected as follows. A Physical Habitat Simulation System (PHABSIM) transect was placed at the top and bottom of 3A after restoration, to provide: (1) the downstream stage– discharge relationship as an input to the River2D model; (2) an upstream water surface elevation for calibration of the River2D model; and (3) part of the bed topography of 3A after restoration. These transects were not used to model habitat. Bed elevation, depth, velocity, substrate and cover data on the PHABSIM transects were collected in June 2003 at 5.3 to 5.4 m3/s for the postrestoration site. Water surface elevations and flows were measured at four flows for each PHABSIM transect. These flows ranged from 2.7 to 40.9 m3/s from January to August 2003. Only the measurements at the 40.9-m3/s flow were collected before the 30 April 2003 peak flow. Examination of plots of the measured water surface elevations versus flow suggested that this peak flow did not alter the stage–discharge relationships at the transects. The remainder of the bed topography data for 3A in 2003, as well as substrate and cover data, were collected using a total station, generally in sets of points going across the channel. Points were placed at changes in slope and to capture changes in substrate and cover. The density of points measured from both sources (PHABSIM transects and total station) used to develop the 2003 postrestoration bed topography for the River2D model was 5.7 points/100 m2. Dominant substrate was visually assessed as the size range of particles that comprised more than 50% of the surface area. For example, if more than 50% of the area was composed of 5.0 to 10.0 mm particle sizes, the dominant substrate was classified as 5.0 to 10.0 mm. The midpoint of the dominant
substrate size range was assumed to be an approximation of the D50 (median) particle size. The cover categories used are given in Gard (2006). A minimum of 50 velocity measurements were collected to validate the velocity predictions of River2D. Velocities measured on the PHABSIM transects were also used to validate the velocity predictions of River2D. Bed topography data for 3A in 2002 and 2004, provided by Graham Matthews and Associates, were used to develop the hydraulic models for 3A in 2002 and 2004. The densities of this bed topography data were 12.2 and 8.3 points/100 m2, respectively, for 2002 and 2004. A substrate of 2.5 to 7.5 cm diameter and no cover were applied to areas inundated at 5.7 to 8.5 m3/s for the hydraulic model of 3A in 2002, based on the as-built conditions for 3A. The substrate and cover distribution for the remainder of 3A in 2002 and for all of 3A in 2004 were based on the data collected in 2003 because substrate and cover distribution data were not collected in 2002 and 2004. This is based on the assumption that the distribution of substrate and cover were not altered by the 17 February 2004 high-flow event. Bed topography, bed roughness and substrate and cover distribution data were entered into River2D to create hydraulic models for 3A after restoration. To minimize the effects of inflow boundary condition specifications, a one-channel-width upstream artificial extension was added to 3A by translating the cross-sectional topography at the top of 3A upstream parallel to the top PHABSIM transect, with a bedslope equal to the water surface elevation slope of 3A. The River2D model used a triangular irregular network grid for hydraulic calculations, with grid elements ranging from 5 m in areas with uniform topography to 0.5 m in areas with rapidly varying topography (Figure 1). The number of grid elements for the 2002 to 2004 3A models ranged from 7,299 to 40,757. Details on the methods used to develop and calibrate the hydraulic models are given in Gard (2006). The calibrated
Figure 1. Example of a triangular irregular network grid used for
Published 2013. This article is a U.S. Government work and is in the public domain in the USA.
hydraulic calculations River Res. Applic. 30: 40–44 (2014) DOI: 10.1002/rra
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files for 3A were used in River2D to simulate hydraulic characteristics for flows of 1.4 to 25.5 m3/s. The calibrated files for 3A were also used to simulate hydraulic characteristics for the average flows in 2002 (5.9 m3/s), 2003 (8.1 m3/s) and 2004 (5.8 m3/s) from the beginning of spawning through the end of redd data collection. Habitat suitability curves (HSC) are used in River2D to translate hydraulic and structural elements of rivers into CSI, calculated as the product of the depth, velocity and substrate suitabilities for spawning, and as the product of the depth, velocity, cover and adjacent velocity suitabilities for fry and juvenile rearing. Adjacent velocity was defined as the fastest velocity within 0.6 m laterally (perpendicular to the flow) of the fish location. Adjacent velocity was based on a bioenergetics mechanism of invertebrate drift being transported from fast-water areas to adjacent slow-water areas, where fry and juvenile salmon reside, by turbulent mixing. Spawning and rearing habitat were calculated using HSC (Gard, 2006) developed from data on fall-run Chinook salmon in the Sacramento River. Habitat was simulated for flows of 1.4 to 25.5 m3/s. The adjacent velocity criteria were incorporated into the rearing habitat calculations using a Geographic Information System postprocessing software. Mann–Whitney U tests (Wilkinson, 1990) were used to determine for 3A in 2002, 2003 and 2004 if there was a significant difference in the CSI predicted by River2D for occupied versus unoccupied locations for spawning. This test is analogous to the transferability test described by Thomas and Bovee (1993). The calibrated River2D simulations at 5.9 m3/s for 3A in 2002, at 8.1 m3/s for 3A in 2003, and at 5.8 m3/s for 3A in 2004 were used with the Sacramento River Chinook salmon spawning HSC to calculate the CSI values predicted by River2D for occupied and unoccupied spawning locations. Unoccupied locations were randomly selected if they met the following criteria: they were farther than 1 m from an occupied location and they were wetted. Eight hundred unoccupied River2D locations per year were selected to ensure that the statistical tests would have sufficient power.
Figure 2. Example of velocity validation. Results are from 3A in
2003, downstream cross-section at a flow of 5.4 m3/s
habitat was still greater than prior to construction (Figure 3). High flows did not have a noticeable effect on the amount of fry and juvenile rearing habitat (Figures 4 and 5). The CSI of occupied locations predicted by River2D (Table I) was significantly greater than the CSI of unoccupied locations at p < 0.05 (Mann–Whitney U test) for fallrun Chinook salmon spawning in 2002, 2003 and 2004. The CSI of both occupied and unoccupied locations were much higher in 2002 than in 2003 and 2004. A substrate that was too small was the cause of most of the occupied locations that were predicted to have a CSI of 0 (Table II). DISCUSSION Changes in habitat caused by high flows can have varying effects on the amount of habitat for anadromous salmonids. Although our work showed decreasing amounts of spawning
RESULTS Typical validation results of the River2D hydraulic model are shown in Figure 2. Both the Clear Creek restoration design and the constructed project showed a substantial increase in spawning WUA (Figure 3) at all flows, and in fry and juvenile rearing WUA (Figures 4 and 5) at low flows compared with prerestoration conditions, but a decrease in fry and juvenile rearing WUA at higher flows. Although channel changes caused by high flows reduced the amount of spawning habitat, compared with the amount available immediately after construction, the amount of spawning
Figure 3. Clear Creek fall-run Chinook salmon spawning flow–
Published 2013. This article is a U.S. Government work and is in the public domain in the USA.
habitat relationships River Res. Applic. 30: 40–44 (2014) DOI: 10.1002/rra
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Table I. Mann–Whitney U tests for spawning CSI Year Occupied n Unoccupied n Occupied median CSI Unoccupied median CSI p Spawning WUA (m2)
Figure 4. Clear Creek fall-run Chinook salmon fry rearing flow–
habitat relationships
habitat associated with high-flow–induced channel changes, Harrison et al. (2011) found an increase in the amount of spawning habitat with time. These results point out the need for models that can simulate the changes in channel topography associated with high-flow events, which could then be used to simulate habitat over time. Such models would allow for a more robust method to conduct adaptive management, in which alternative designs for restoration projects could be simulated to assess their sustainability. Existing hydraulic models can predict where bed material will be scoured on a spatially explicit basis because of high-flow events. However, they lack the capability to determine what the resulting bed topography will be after
2002
2003
2004
85 800 0.57 0.41 0.003 3,639
79 800 0.13 0
