THE INFLUENCE OF VARIABLE HABITAT SUITABILITY CRITERIA ON PHABSIM HABITAT INDEX RESULTS

The Physical Habitat Simulation System (PHABSIM) still probably remains as the most widespread habitat method used to establish inflow standards or to link habitat temporal variations with fish population dynamics. However, statistical uncertainties around the PHABSIM main output, the weighted usable area (WUA) over discharge curves, are usually ignored. Here, we assess the uncertainty in WUA curves and derived habitat duration curves induced by the variability around the PHABSIM biological model, the habitat suitability criteria, using brown trout Salmo trutta as the model species. Bootstrap analyses showed that the uncertainty around the WUA curves was rather high when bootstrap sample (BS) size was low and differed among age classes, being generally lower for young‐of‐the‐year (YOY). Width of 95% confidence intervals for maximum WUA magnitude increased with decreasing BS size, ranging from 19.3% for YOY trout at the largest BS size (40 transects, 270 habitat use observations) to 146% for juveniles at the smallest BS size (nine transects, 60 habitat use observations). The uncertainty arose primarily from the construction of the channel index variable. Nevertheless, results showed that the uncertainty in WUA values could be reduced down to acceptable levels by using general functional channel index categories. Likewise, the shape of WUA curves was also highly variable when BS was small. These patterns resulted in habitat duration curves being highly uncertain, much more in their amplitude than in their shape. Uncertainty about the flows corresponding to different habitat exceedance values increased with decreasing probability of exceedance. Width of peak flow confidence intervals ranged from 3.3% for YOY trout at the largest BS size to 226% for adults at the smallest BS size. Yet such levels of uncertainty do not necessarily entail critical errors in the decision‐making process because large variability in flow peak does not necessarily lead to large variability in WUA magnitude.     

Assessment of the water surface profile model: Accuracy of predicted instream fish habitat conditions in low-gradient,warmwater streams

The Instream Flow Group's (U.S. Fish and Wildlife Service) Physical Habitat Simulation (PHABSIM) model, the major component of the incremental methodology (IFIM) is presently the most widely employed instream flow assessment procedure. PHABSIM consists of both biological and hydrological components. The Water Surface Profile (WSP) hydrologic model is commonly recommended and employed in many PHABSIM applications. While several recent studies have critically addressed and questioned the validity of PHABSIM as a management tool from a biological perspective, there has been surprisingly limited attention given to problems of use, accuracy, bias, and the effect of errors in the WSP hydraulic simulation on the final PHABSIM output (i.e. weighted usable area (WUA) estimates). Therefore, the purpose of this study was to examine the effectiveness of the WSP hydraulic model for predicting hydraulic conditions in low-gradient, warmwater streams in east-central Illinois. Attempts were made to calibrate the WSP model at four locations on the Salt Fork and Middle Fork rivers and compare simulated results to actual measured conditions at different discharges. We conclude that in low-gradient warmwater streams, the WSP model: (1) does not adequately simulate low-flow habitat conditions, due to an inability to calibrate the model; (2) is, at best, difficult to calibrate, even within hydraulically uniform channels; (3) requires several field measurements and calibrations to simulate a sufficiently wide range of naturally occurring flows: (4) provides poor estimates of cell depth and velocity; and, results in highly erratic and often poor estimates of WUA for adults and fry of smallmouth bass. Finally, our results indicate that similar or better estimates of actual WUA can be attained by monitoring the distributions of depth, velocity, and substrate at a series of representative transects at different discharges and interpolating WUA from observed field data using less expensive and time consuming regression models.     

Habitat suitability curves for brown trout (Salmo trutta fario L.) in the River Adda,Northern Italy: comparing univariate and multivariate approaches

Habitat suitability of brown trout (Salmo trutta fario) was studied in the upper portion of the Adda River, Northern Italy. Measurements were made for 528 individuals distributed in two life‐stage classes, adult and juvenile, based on body length. In order to provide basic biological information for the physical habitat simulation (PHABSIM) system of the instream flow incremental methodology (IFIM) in the Italian regulated rivers, habitat suitability curves (HSCs) have been developed with respect to several microhabitat riverine parameters. Initially, current velocity, water depth, substrate class size and cover were analysed with an univariate approach, then bivariate habitat suitability models were developed from depth and velocity data. The comparison of experimental univariate HSCs with those from the literature outlined some differences that can essentially be explained by characteristics of the investigated river, confirming the necessity of using site‐specific curves in relation to each experimental study area. To compare the univariate and bivariate approaches, the weighted usable area (WUA)–discharge relationships were calculated using both types of HSCs. Response curves obtained from the two approaches turned out to be quite different. In PHABSIM habitat modelling, HSCs univariate functions need to be aggregated to produce the WUA–discharge relationship. A multiplicative criterion is generally used for the combined suitability factor; by means of this aggregation criterion all variables have equal weight. According to bivariate models, depth is much more important than velocity in defining habitat suitability requirements. Copyright © 2001 John Wiley & Sons, Ltd.     

Response of the benthic macroinvertebrate community in a northern Michigan stream to reduced summer streamflows

We evaluated the response of benthic macroinvertebrates in a Michigan trout stream to flow reduction by diverting water from a 602 m reach of Hunt Creek from June through August of 1994, 1997 and 1998. We also assessed the utility of the Physical Habitat Simulation system (PHABSIM) in predicting the response of benthic insects to water withdrawals by testing the assumption of a positive linear relationship between modelled habitat (weighted usable area, WUA) and the density of 13 benthic insect families. Our findings showed that the density of filter feeding and grazing insect taxa, as well as insects classified as obligate erosional zone taxa, declined significantly in the dewatered (treatment) zone (TZ) when 90% of flow was diverted. Density of Ephemeroptera, Plecoptera and Trichoptera (EPT) taxa in the TZ was significantly lower when 90% of water was diverted as compared to density at baseflow or when flow was reduced by 50%. The density of all insects in an upstream reference zone riffle (RZ), where flow was not altered, did not change among experimental periods. Although overall reductions in the density of benthic insects at 90% flow reduction coincided with lower PHABSIM predictions of WUA, we found poor linear correlation between WUA at different flows and the density of the 13 benthic insect families for which WUA was modelled. The low proportion of variation explained by WUA for all families modelled suggests that WUA alone is not an accurate predictor of benthic insect density. Resource managers should consider the potential consequences of water withdrawals to all components of stream communities, including benthic macroinvertebrates. However, caution should be applied when using the PHABSIM technique in groundwater‐fed streams such as Hunt Creek, because most relationships between WUA and benthic insect density were insignificant. Copyright © 2006 John Wiley & Sons, Ltd.     

Ability of phabsim to predict chinook salmon spawning habitat

PHABSIM, part of the Instream Flow Incremental Methodology, was used to predict the spawning habitat used by chinook salmon in a 600 m long section of the Nechako River, British Columbia, Canada. Predictions of the model were compared to the location and amount of habitat actually used by adult chinook salmon in 1974, 1980, and 1986. About 3800 m² (70 per cent) of the spawning area actually used by the population were predicted as unusable by the ‘best’ prediction, while 87 per cent of the area predicted as usable has never had recorded use. The ‘best’ prediction resulted from using close transect spacing, frequent measurements along the transect, river-specific habitat suitability criteria, and modelling habitat at the fish's position near the stream bottom. Depending upon the spacing of the transects and the habitat suitability criteria used, PHABSIM predicted 210 per cent to 660 per cent more spawning habitat was available than historically had ever been used. Chinook salmon in the Nechako River spawn mainly on the upstream face of dunes, therefore, the assumption in PHABSIM that conditions predicted at the transects remain unchanged upstream and downstream part way to the adjacent transects was false. This assumption resulted in about two-thirds of the correct predictions being made for the wrong reason. The accuracy of PHABSIM's predictions for spawning might be improved by incorporating an index of river bottom topography or velocity gradient into the model.     

Assessing discharge use by spawning Atlantic salmon: A comparison of discharge electivity indices and PHABSIM simulations

The locations used by spawning Atlantic salmon (Salmo salar L.) in a reach of the Girnock Burn, Scotland, were monitored over three successive years. Reach discharge was estimated for each spawning observation using a conversion factor applied to continuous flow data from a gauge located in the catchment. Data on the availability and use of different discharges were used to construct a discharge electivity index for the reach. The index was compared to output from a Physical HABitat SIMulation (PHABSIM) model of the reach. Spawning fish used relatively high discharges, with the highest electivity value being for a discharge approximately three times the reach median flow. The electivity index and the PHABSIM weighted usable area (WUA) versus discharge curve were similar across the low flow range and both suggested similar optimum discharges for spawning (1.1 and 1.4 m³ s^?1 respectively). However, electivity values suggested unsuitable conditions were reached at discharges greater than 1.4 m³ s^?1 whereas PHABSIM predicted relatively high WUA values at discharges up to 2 m³ s^?1. Electivity indices provide an insight into discharge selection that is not dependent on hydraulic simulations or assumptions about microhabitat (depth, velocity, substrate) preferences. Moreover, they can be used to assess discharge suitability in hydraulically complex streams where the one‐dimensional hydraulic models used by PHABSIM may be inappropriate. However, unlike PHABSIM, they cannot be used to predict the suitability of flows outside observed discharge ranges and so are limited in their application. Further work is required to refine the methodology and assess its transferability to other streams. Nonetheless, indices may represent a useful tool that can be used to complement other methods of assessing instream flow needs. Copyright © 2002 John Wiley & Sons, Ltd.     

Effects of variation in streamflow and channel structure on smallmouth bass habitat in an alluvial stream

We evaluated the effects of streamflow‐related changes in channel shape and morphology on the quality, quantity, availability and spatial distribution of young‐of‐year and adult smallmouth bass Micropterus dolomieu habitat in an alluvial stream, the Baron Fork of the Illinois River, Oklahoma. We developed Habitat Suitability Criteria (HSC) for young‐of‐year and adult smallmouth bass to assess changes in available smallmouth bass habitat between years, and compare predicted smallmouth bass Weighted Usable Area (WUA) with observed WUA measured the following year. Following flood events between 1999 and 2000, including a record flood, changes in transect cross‐sectional area ranged from 62.5% to 93.5% and channel mesohabitat overlap ranged from 29.5% to 67.0% in study three study reaches. Using Physical HABitat SIMulation (PHABSIM) system analysis, we found that both young‐of‐year and adult smallmouth bass habitat were differentially affected by intra‐ and inter‐annual streamflow fluctuations. Maximum WUA for young‐of‐year and adults occurred at streamflows of 1.8 and 2.3 m³ s^?1, respectively, and WUA declined sharply for both groups at lower streamflows. For most microhabitat variables, habitat availability was similar between years. Habitat suitability criteria developed in 1999 corresponded well with observed fish locations in 2000 for adult smallmouth bass but not for young‐of‐year fish. Our findings suggest that annual variation in habitat availability affects the predictive ability of habitat models for young‐of‐year smallmouth bass more than for adult smallmouth bass. Furthermore, our results showed that despite the dynamic nature of the gravel‐dominated, alluvial Baron Fork, HSC for smallmouth bass were consistent and transferable between years. Published in 2008 by John Wiley & Sons, Ltd.     

Variability of results from the use of PHABSIM in estimating habitat area

The estimation of the area of a stream reach suitable as habitat for an aquatic species by the Instream Flow Incremental Methodology is described. An important component of the methodology is PHABSIM, which is a collection of computer programs whereby useable stream area is computed as a function of discharge. This comprises a variety of options for both hydraulic and habitat simulation. A single data set is used to calculate the useable area at one discharge for three life stages of brown trout, using various options in habitat simulation. The results are shown to vary greatly according to the particular combination of options selected, so unless calculations are founded on biologically realistic assumptions the potential within PHABSIM for the ?fudging”? of results is considerable.     

BOOTSTRAP SAMPLING IS WITH REPLACEMENT: A COMMENT ON AYLLÓN ET AL. (2011)

The bootstrap can be used to estimate confidence intervals for complex statistics such as weighted usable area, the habitat index calculated by the Physical Habitat Simulation System (PHABSIM) and related models. Use of the bootstrap entails sampling with replacement from the original sample, such as a set of PHABSIM transects. Because the method has been improperly applied to PHABSIM transects in several instances, I explain in detail why bootstrap sampling is with replacement. Copyright © 2011 John Wiley & Sons, Ltd.     

Linking a spatially explicit watershed model (SWAT) with an in‐stream fish habitat model (PHABSIM): A case study of setting minimum flows and levels in a low gradient,sub‐tropical river

As changes in landuse and the demand for water accelerate, regulators and resource managers are increasingly asked to evaluate water allocation against the need for protection of in‐stream habitat. In the United States, only a small number of river basins have the long‐term hydrograph data needed to make these assessments. This paper presents an example of how to bridge the conceptual and physical divide between GIS‐based watershed modelling of basin‐discharge and in‐stream hydraulic habitat models. Specifically, we used a Soil and Water Assessment Tool (SWAT) model for the Hillsborough River to produce data for use in a Physical HABitat SIMulation (PHABSIM) model of the same river. This coupling of models allowed us to develop long‐term discharge data in ungauged river systems based on watershed characteristics and precipitation records. However this approach is not without important limitations. Results confirm that accuracy of the SWAT‐predicted hydrograph declines significantly when either the DEM resolution becomes too coarse or if DEM data are resampled to a coarser or finer resolution. This is due to both changes in the size and shape of the river basin with the varying DEMs and subsequent shifts in the proportions of land use, soils and elevation. Results show the use of 30 m DEMs produced hydrographic patterns amenable for using in‐stream habitat protocols like PHABSIM model, especially where little or no hydrographic and land use information exists. Copyright © 2010 John Wiley & Sons, Ltd.     

Evaluating Uncertainty in Physical Habitat Modelling in a High‐Gradient Mountain Stream

Predictions of habitat‐based assessment methods that are used to determine instream flow requirements for aquatic biota are uncertain, but instream flow practitioners and managers often ignore those uncertainties. Two commonly recognized uncertainties arise from (i) estimating the way in which physical habitat within a river changes with discharge and (ii) the suitability of certain types of physical habitat for organisms. We explored how these sources of uncertainty affect confidence in the results of the British Columbia Instream Flow Methodology (BCIFM), which is a commonly used transect‐based habitat assessment tool for small‐scale water diversions. We calculated the chance of different magnitudes of habitat loss resulting from water diversion using a high‐gradient reach of the North Alouette River, BC, as a case study. We found that uncertainty in habitat suitability indices for juvenile rainbow trout generally dominated uncertainty in the results of the BCIFM when large (>15) numbers of transects were used. In contrast, with small numbers of transects, variation in physical habitat among sampled transects was the major source of uncertainty in the results of the BCIFM. Presentations of results of the BCIFM in terms of probabilities of different amounts of habitat loss for a given flow can help managers prescribe instream flow requirements based on their risk tolerance for fish habitat loss. Copyright © 2015 John Wiley & Sons, Ltd.     

Spatial distribution and geomorphic condition of fish habitat in streams: an analysis using hydraulic modelling and geostatistics

Reach‐scale physical habitat assessment scores are increasingly used to make decisions about management. We characterized the spatial distribution of hydraulic habitat characteristics at the reach and sub‐reach scales for four fish species using detailed two‐dimensional hydraulic models and spatial analysis techniques (semi‐variogram analyses). We next explored whether these hydraulic characteristics were correlated with commonly used reach‐scale geomorphic assessment (RGA) scores, rapid habitat assessment (RHA) scores, or indices of fish biodiversity and abundance. River2D was used to calculate weighted usable areas (WUAs) at median flows, Q₅₀, for six Vermont streams using modelled velocity, depth estimates, channel bed data and habitat suitability curves for blacknose dace (Rhinichthys atratulus), brown trout (Salmo trutta), common shiner (Notropis cornutus) and white sucker (Catostomus commersoni) at both the adult and spawn stages. All stream reaches exhibited different spatial distributions of WUA ranging from uniform distribution of patches of high WUA to irregular distribution of more isolated patches. Streams with discontinuous, distinct patches of high score WUA had lower fish biotic integrity measured with the State of Vermont's Mixed Water Index of Biotic Integrity (MWIBI) than streams with a more uniform distribution of high WUA. In fact, the distribution of usable habitats may be a determining factor for fish communities. A relationship between predicted WUAs averaged at the reach scale and RGA or RHA scores was not found. Future research is needed to identify the appropriate spatial scales to capture the connections between usable patches of stream channel habitat. Copyright © 2008 John Wiley & Sons, Ltd.     

Application of physical habitat simulation (PHABSIM) modelling to modified urban river channels

Prediction of changes to in‐stream ecology are highly desirable if decisions on river management, such as those relating to water abstractions, effluent discharges or modifications to the river channel, are to be justified to stakeholders. The physical habitat simulation (PHABSIM) system is a well‐established hydro‐ecological model that provides a suite of tools for the numerical modelling of hydraulic habitat suitability for fish and invertebrate species. In the UK, the most high‐profile PHABSIM studies have focused on rural, groundwater‐dominated rivers and have related to low flow issues. Conversely, there have been few studies of urban rivers. This paper focuses on the application of PHABSIM to urban rivers and demonstrates how sensitivity analyses can be used to assess uncertainty in PHABSIM applications. Results show that physical habitat predictions are sensitive to changes in habitat suitability indices, hydraulic model calibration and the temporal resolution of flow time‐series. Results show that there is greater suitable physical habitat over a wider range of flows in a less engineered river channel when compared to a more engineered channel. The work emphasizes the need for accurate information relating to the response of fish and other organisms to high velocities. Copyright © 2004 John Wiley & Sons, Ltd.     

Optimizing a Standardized Electrofishing Sampling Protocol for Warmwater Resident Sportfish in the Tallapoosa River,Alabama, USA

A two‐year electrofishing study was initiated in the Tallapoosa River, Alabama, to identify an optimal standardized sampling program for three principal resident sportfish: Alabama bass Micropterus henshalli, redbreast sunfish Lepomis auritus, and redeye bass Micropterus coosae. Samples were conducted in spring (May), summer (July), and fall (October) in 2010 and 2011 from seven 1‐h transects. Spring samples of Alabama bass had lower catch per effort (CPE) and were more skewed towards fish between 200 and 300 mm total length (TL) than samples in other seasons; whereas, fall samples collected more redeye bass >200 mm TL but CPE was similar among seasons. Fewer, but larger, redbreast sunfish were sampled during fall compared with other seasons. Mean CPE of all three species was independent of transect duration. The total time spent electrofishing and processing fish in order to estimate a mean CPE with a specified precision was a function of transect duration and CPE. More effort was needed as CPE decreased for most species, but the relations between transect duration and total effort were parabolic. A precision of within 10% of the mean CPE was unattainable for most species as a result of logistic considerations. Based on the results of this study, it appears that fall is the optimal sampling time for these species in the Tallapoosa River and the optimal transect duration is likely 10 min. At a precision level of 20% of the mean, the number of 10‐min transects required ranged from 5 to 40, with a total sample time for each individual species of 0.82–7.16 h. Copyright © 2014 John Wiley & Sons, Ltd.     

Salmonid habitat modelling studies and their contribution to the development of an ecologically acceptable release policy for Kielder Reservoir,North‐east England

1. Kielder Reservoir regulates the Rivers North Tyne and Tyne. It provides a regular supply of water for downstream users, supports abstractions for a major water transfer scheme and provides hydroelectric power (HEP). Kielder's release regime typically alternates between a 1.3 m³ s⁻¹ compensation flow and 10–15 m³ s⁻¹ HEP releases of between 3 and 7 days in duration. Occasionally releases of up to 30 m³ s⁻¹ are made for the purpose of encouraging fish runs, for recreational events or to help in water quality management. The impacts of this release regime on Atlantic salmon (Salmo salar) and brown trout (S. trutta) habitat at four sites on the North Tyne are assessed and alternative regimes, designed to minimize impacts, are presented. 2. There is no evidence that the compensation flow results in extreme loss of instream habitat. A discharge of 1.3 m³ s⁻¹ ensures that water is maintained over most of the channel area at sites representative of upper, middle and lower sections of the North Tyne. This discharge lies above breaks in slope of respective site discharge versus wetted area curves; thus, disproportionate increases in discharge would be needed to increase wetted area. Simulations using the Physical Habitat Simulation System (PHABSIM) suggest that the compensation flow provides between 50% and 90% of the maximum possible weighted usable area (WUA) for juvenile (0+) salmonids. 3. During HEP releases, juvenile salmonid habitat (WUA) apparently falls to between 20 and 40% of site maxima. Newly emerged juvenile fish (March and April) are most affected by HEP releases because they are relatively small (25 mm in length) and water temperatures are relatively low at this time of year. During March and April, critical near‐bed displacement velocities for newly emerged fish may be exceeded across large parts (80%) of sites up to 8 km downstream from Kielder Reservoir; fish would either be displaced downstream or forced to relocate to flow refuge areas. 4. The availability of Atlantic salmon spawning habitat (WUA) at a key site is limited by the compensation flow; 1.3 m³ s⁻¹ provides approximately one third of the habitat available at the optimum discharge (4 m³ s⁻¹). At this site, a discharge of approximately 2 m³ s⁻¹ is needed to ensure most of the bed is inundated by water. Regulation has reduced the duration of flows exceeding 2 m³ s⁻¹ from 90 to 60% of the spawning season. 5. Simulations suggest that when discharge drops from 30 m³ s⁻¹ to the compensation flow, up to 60% of the optimum spawning habitat available at the former discharge may be left stranded (dry). This could potentially lead to egg or alevin mortality. 6. PHABSIM simulations suggest that increasing the compensation flow to 4 m³ s⁻¹ during the spawning period (November and December) is likely to increase the availability of suitable spawning habitat. Also, increasing the compensation flow to 2 m³ s⁻¹ during the incubation period (January through March) would minimize redd stranding. Reductions in the number of HEP releases in March and April would limit the extent to which newly emerged fish are exposed to velocities that potentially displace them. Such changes to the Kielder release regime may have implications for water resource management. While it is important that the biological instream flow requirements of the North Tyne are incorporated into the Kielder operating policy, these should be integrated along with the need for channel maintenance flows, downstream water supply abstractions and HEP generation, as well as for transfers of water to other catchments. Copyright © 2000 John Wiley & Sons, Ltd.     

Estimating discharge in gravel‐bed river using non‐contact ground‐penetrating and surface‐velocity radars

Discharge measurement is a critical task for gravel‐bed channels. Under high‐flow conditions, the elevation of the riverbed changes significantly by intensive torrential flow. The stage–discharge relations commonly used for stream discharge estimation may no longer be adequate. The contact‐type velocity measuring is also subject to measurement errors and/or instrument failures by the high‐flow velocities, driftwood, stumps, and debris. This study developed a new real‐time method to estimate river discharge in gravel‐bed channels. A systematic measuring technology combining ground‐penetrating radar and surface‐velocity radar was employed. The rating curves representing the relations of water surface velocity to the channel cross‐sectional mean velocity and flow area were established. Stream discharge was then deduced from the resulting mean velocity and flow area. The proposed method was examined in a steep gravel‐bed reach of the Cho‐Shui River in central Taiwan. The estimated stream discharge during three flood events were compared to the prediction by using the stage–discharge relation and the index‐velocity method. The proposed method of this study is capable of computing reasonable values of discharge for an entire flood hydrograph, whereas the other two methods tend to produce large extrapolation errors. Moreover, when the computed discharge is used in 2D flood flow simulation, the proposed method demonstrates better performance than the commonly used stage–discharge and index‐velocity methods.     

逐步图解法淹没式堰流公式推流的使用范围

堰闸水文站出现淹没式堰流时可以使用逐步图解法定线推流,但小水位差时用自记水位推流,计算流量的误差可能很大。通过对淹没式堰流计算流量的不确定度的分析计算,得到水位差的百分不确定度XΔz,根据计算流量的不确定度要求,推算得到满足计算流量不确定度要求的水位差的范围:对于开宽大于2.0 m、下游水头大于0.5 m的堰闸站出现淹没式堰流时,只有水位差大于0.14 m时,才能使用自记水位推流。     

PREDICTING HABITAT RESPONSE TO FLOW USING GENERALIZED HABITAT MODELS FOR TROUT IN ROCKY MOUNTAIN STREAMS

Dams and water diversions can dramatically alter the hydraulic habitats of stream ecosystems. Predicting how water depth and velocity respond to flow alteration is possible using hydraulic models, such as Physical Habitat Simulation (PHABSIM); however, such models are expensive to implement and typically describe only a short length of stream (10² m). If science is to keep pace with development, then more rapid and cost‐effective models are needed. We developed a generalized habitat model (GHM) for brown and rainbow trout that makes similar predictions to PHABSIM models but offers a demonstrated reduction in survey effort for Colorado Rocky Mountain streams. This model combines the best features of GHMs developed elsewhere, including the options of desktop (no‐survey) or rapid‐survey models. Habitat–flow curves produced by PHABSIM were simplified to just two site‐specific components: (i) Q95h (flow at 95% of maximum habitat) and (ii) Shape. The Shape component describes the habitat–flow curves made dimensionless by dividing flow increments by Q95h and dividing habitat (weighted usable area) increments by maximum habitat. Both components were predicted from desktop variables, including mean annual flow, using linear regression. The rapid‐survey GHM produced better predictions of observed habitat than the desktop GHM (rapid‐survey model explained 82–89% variance for independent validation sites; desktop 68–85%). The predictive success of these GHMs was similar to other published models, but survey effort to achieve that success was substantially reduced. Habitat predicted by the desktop GHM (using geographic information system data) was significantly correlated with the abundance of large brown trout (p < 0.01) but not smaller trout. Copyright © 2013 John Wiley & Sons, Ltd.     

Determination of ecologically acceptable flows in rivers with seasonal changes in the density of macrophyte

The Instream Flow Incremental Methodology (IFIM) is a procedure that has been applied to the rivers of many countries to determine the relationship between discharge and a measure of the physical habitat area available to aquatic species. PHABSIM is a software package that is used to perform the calculations required for the IFIM procedure. Published data on instream macrophyte growth in chalk streams are used here to test the seasonal effects of plant growth in a hypothetical channel. The results show how these effects can significantly distort PHABSIM results. The predicted weighted useable area can differ by as much as 34% depending on the season used for the principal calibration of the Water Surface Profile module (WSP) of PHABSIM. An algorithm is proposed for use with PHABSIM which allows the effects of changes in macrophyte biomass to be included.     

Variability in flow–habitat relationships as a function of transect number for PHABSIM modelling

A bootstrap analysis was used to assess the variability in flow–habitat relationships for juvenile and adult rainbow trout (Oncorhynchus mykiss) in the Cache La Poudre River as a function of the number of Physical Habitat Simulation System (PHABSIM) transects. The bootstrap analysis was conducted by selecting without replacement different numbers of transects, ranging from six to 40, from a pool of 107 transects. The variability in flow–habitat relationships, as quantified by the 95% confidence interval for the flow with the peak habitat, decreased with increasing numbers of transects, and was greater for juveniles than for adults. The 95% confidence limits ranged from 9% for adult trout with 40 transects to 73% for juvenile trout with six transects. The results of this study can be used in negotiations for the number of transects selected during scoping of instream flow studies, as well as in assessing the relative confidence that should be placed in flow–habitat relationships for different species and life stages. Published in 2005 by John Wiley & Sons, Ltd.