Hydraulic Metrics Research Articles

Momentum fluxes across multiple mixing interfaces subject to partially-distributed submerged canopy flows

Partially-distributed submerged canopy flows (PSCFs), characterized by the presence of multiple mixing interfaces, are a common feature in riverine and wetland systems. These flows are subject to shear-induced instabilities at the mixing interfaces, which tend to generate multi-dimensional large-scale vortices (LSVs). Yan et al. (2022a) have highlighted the presence of both expected canopy shear layers and unexpected three-dimensional hydrodynamic features in PSCFs. In this paper, we focus on quantitatively analyzing the contribution of different transport mechanisms to individual momentum fluxes, and on identifying the underlying similarity in these fluxes. The results indicate that advection momentum fluxes, generated by secondary circulations (SCs), are equally important as LSVs-driven diffusion momentum fluxes near the mixing interfaces. LSVs transfer momentum from the outer free waters through turbulent diffusion to the canopy interior, while momentum is consumed by the SCs in the area across the interfaces. Consequently, the coexistence of SCs-driven advection and LSVs-driven diffusion leads to particular hydrodynamic features such as near-bed velocity deflection in the junction, outward shift of horizontal mixing layer, significant transverse variation of energy slope and so on. In addition, the observations confirm that the value of the momentum fluxes highly depends on canopy geometric and hydraulic factors, enabling the achievement of the dependency of several momentum fluxes on canopy geometric and hydraulic metrics with the self-similarity analysis. This research offers new insights into the essential physical interpretation of three-dimensional flow behavior subject to multiple mixing interfaces in PSCFs.

Can hydraulic measures of river conditions improve our ability to predict ecological responses to changing flows? Flow velocity and spawning of an iconic native Australian fish

Ecological responses to changing riverine flows are often evaluated by describing the relationship between river discharge and response. However, aquatic organisms experience the hydraulics (i.e. velocity, shear stress, depth) of a river, not its discharge. Hydraulic characterizations of riverine habitats may improve our ability to predict ecological responses. We used two-dimensional hydraulic models to translate river discharge into flow velocity. We used discharge and reach-averaged velocity, along with water temperature and 8 years of field observations of fish spawning, to develop predictive models of the spawning of golden perch (Macquaria ambigua) in the Goulburn River, south-east Australia. Probability of spawning was positively related to both discharge and reach-averaged velocity. Water temperature was critical for enabling the flow response, and antecedent flows prior to spawning had a weak positive effect. Against expectations, there was little difference in predictive uncertainty for the effect of flows when reach-averaged velocity was used as the main predictor rather than discharge. The lower Goulburn River has a relatively simple channel and so discharge and velocity are monotonically related over most flows. We expect that in a more geomorphically complex environment, improvement in predictive ability would be substantial. This research only explores one example of a hydraulic parameter being used as a predictor of ecological response; many others are possible. The extra effort and expense involved in hydraulic characterization of river flows is only justified if our understanding of flow-ecology relationships is substantially improved. Further research to understand which environmental responses might be best understood through different hydraulic parameters, and how to better characterize hydraulic characteristics relevant to riverine biota, would help inform decisions regarding investment in hydraulic models. Regardless, hydraulics offers a more process-based assessment of ecological responses to changing flows, has the potential to facilitate mechanistic understanding rather than just associations, and provides the opportunity to translate hydraulic metrics that drive ecological responses across river systems of differing sizes. However, while considering ecological responses in terms of river hydraulics is more physically realistic, our results suggest that average hydraulic conditions may not result in an improved ability to predict the effects of changing flows.

An experimental study: effects of boulder placement on hydraulic metrics of instream habitat complexity

Boulder placement is a common method to restore degraded instream habitats by enhancing habitat complexity. This experimental study is the foremost attempt to systematically investigate the influence of rock-ramp boulder placement with varying boulder concentration and flow rate on habitat hydraulic complexity metrics, including the kinetic energy gradient and modified recirculation metrics. By adding boulders to a reach, the modified recirculation metric increased by one order of magnitude for all boulder concentrations. Based on the studied metrics, boulder placement with the highest boulder concentration (λ = 8.3%) resulted in the greatest habitat hydraulic complexity. A set of relationships of moderate strength were proposed to predict the metrics in reaches with boulders by having information about only boulder concentration, habitat characteristic size, and reach-averaged flow characteristics. Based on the available data from the literature, boulder placement especially at higher concentrations may provide suitable habitats for several riverine fish species. Further studies are needed to establish a reliable linkage between the metrics and instream species, to test a wider variety of parameters for verifying and improving the range of applicability of the proposed relationships, and to find the structural configuration at which the habitat complexity is maximized or optimized for a certain species.

Topological and hydraulic metrics-based search space reduction for optimal re-sizing of water distribution networks

Abstract Pipe re-sizing of water distribution networks (WDNs) aims at improving the service performance to the required level, while minimizing the cost of replacing pipes in the network. The main challenge comes from the identification of the most effective pipes to re-size from a large number of interacting components. Performing a global search over all pipes in large WDNs does not guarantee a feasible and efficient solution due to the enormous search space, even by employing advanced algorithms, e.g., evolutionary algorithms. This paper proposes a novel method to reduce the search space for optimal re-sizing based on topological metrics from Complex Network Theory and hydraulic metrics, while providing suboptimal solutions comparable to the full search solutions, i.e., considering all pipes as candidates. The topological metrics are based on the edge-betweenness tailored for WDN analysis. Hydraulic metrics are unit head loss and flow rates of pipes computed based on simulation of the WDN in the current configuration. The optimal re-sizing plans obtained, particularly those using edge betweenness, were tested on a real WDN. The results are comparable with the full search solutions but they are much more efficient to obtain and require replacing mostly contiguous pipes, i.e., easier for practical fieldwork.

Vegetation disturbances and flood energy during an extreme flood on a sub‐tropical river

AbstractThe advent of 2D hydraulic modelling has improved our understanding of flood hydraulics, thresholds, and dynamic effects on floodplain geomorphology and riparian vegetation at the morphological‐unit scale. Hydraulic concepts of bed shear stress, stream power maxima, and energy (cumulative stream power) have been used to characterize floods and define their geomorphic effectiveness. These hydraulic concepts were developed in the context of reach‐averaged, 1D hydraulic analyses, but their application to 2D model results is problematic due to differences in the treatment of energy losses in 1D and 2D analyses. Here we present methods for estimating total and boundary resistance from 2D modelling of an extreme flood on a subtropical river. Hydraulic model results are correlated with observations of the flood impacts on floodplain geomorphology and the riparian vegetation to identify thresholds and compute variants of flood energy. Comparison of LiDAR data in 2011 and 2014 shows that the 2011 flood produced 2–4 m of erosion on floodplain bars that were previously forested or grass‐covered. Deposition on flood levees, dunes, and chute bars was up to 3.4 m thick. Various hydraulic metrics were trialled as candidates for thresholds of vegetation disturbance. The accuracy of thresholds using metrics extracted at the flood peak (i.e. boundary resistance and stream power maxima) was similar to that using energy as a threshold. Disturbance to forest and grass on vegetated bars was associated with stream powers of >834 W/m2and unit flows of >26 m2/s, respectively. Correlation of the hydraulic metrics with erosion and deposition depths showed no substantial improvement in using flood energy compared to metrics extracted at the flood peak for describing erosion and deposition. The extent of vegetation disturbances and morphological adjustments was limited for this extreme flood, and further 2D studies are needed to compare disturbance thresholds across different environments.

Post-disaster sequential recovery planning for water distribution systems using topological and hydraulic metrics

Multiple pipeline failures in water distribution systems (WDS) caused by natural hazards such as earthquakes can significantly reduce the functionality of the systems. After a natural disaster, a quick recovery of WDS is desirable to ensure that critical facilities have access to clean water. However, experience from recent disasters has shown that the recovery period for WDS can be long. The recovery period depends on various factors, such as available resources, budget, etc. As such, all the failed pipelines cannot be repaired at the same time. Hence, utilities need to prioritise damaged pipelines and perform the repair in such a way that the functionality of the WDS is optimised. Post-event system functionality gain may vary significantly depending on the choice of sequential recovery paths. Unlike other infrastructures, the functionality of WDS is not only dependent on topological integrity but also on hydraulic performance. In this study, a post-disaster recovery planning model for WDS is proposed. The restoration process is modelled in terms of topological efficiency, hydraulic resilience and hydraulic availability. The optimal recovery sequence is determined based on the recovery effectiveness estimated by the area under each recovery sequence curves. The proposed method is illustrated for a moderate size WDS.

Urban Streamflow Impact Assessment (USIA): a novel approach for protecting urbanising waterways and providing the justification for integrated water management

ABSTRACT As urban populations expand globally, the associated increase in urban land cover directly impacts the social and environmental amenity of natural assets, including waterways. The primary driver of urban waterway degradation changes in land uses which results in altered hydrology – from stormwater runoff, and where present, wastewater treatment plant discharge. Whilst the impacts of pollutants are relatively well regulated via public policy, a gap remains for the management of flow regime modification. The Urban Streamflow Impact Assessment (USIA) was developed to fill this management and planning knowledge gap. The approach begins with the identification of waterway values (social, ecological and geomorphic) then explicitly links these values to streamflow characteristics using hydraulic and hydrologic metrics. USIA was applied to a case study in Western Sydney and demonstrated the loss of values associated with ‘business-as-usual’ approaches to stormwater and wastewater management. Conventional stormwater management approaches do not remove enough excess flow to meet reasonable outcomes for the waterway. This excess runoff is increasingly seen as a resource and opportunity for improving water security and liveability. USIA is consistent with regulatory frameworks and can be applied across developing and established urban catchments to provide explicit input to planning controls. The approach is appropriate at multiple scales, informing urban planning from a broad strategic level through to detailed design. By linking social and ecological values with geomorphic and flow requirements, the approach enables an understanding of which management approaches could allow desirable waterway outcomes to be met.

How alternative urban stream channel designs influence ecohydraulic conditions

Streams draining urban catchments ubiquitously undergo negative physical and ecosystem changes, recognized to be primarily driven by frequent stormwater runoff input. The common management intervention is rehabilitation of channel morphology. Despite engineering design intentions, ecohydraulic benefits of urban channel rehabilitation are largely unknown and likely limited. This investigation uses an ecohydraulic modeling approach to investigate the performance of alternative channel design configurations intended to restore key ecosystem functioning in urban streams. Channel reconfiguration design scenarios, specified to emulate the range of channel topographic complexity often used in rehabilitation are compared against a reference ‘natural’ scenario using ecologically relevant hydraulic metrics. The results showed that the ecohydraulic conditions were incremental improved with the addition of natural oscillations to an increasing number of individual topographic variables in a degraded channel. Results showed that reconfiguration reduced excessive frequency of bed mobility, loss of habitat and hydraulic diversity particularly as more topographic variables were added. However, the results also showed that none of the design scenarios returned the ecohydraulics to their reference conditions. This indicate that channel-based restoration can offer some potential changes to hydraulic habitat conditions but are unlikely to completely mitigate the effects of hydrologic change. We suggest that while reach-scale channel modification may be beneficial to restore urban stream, addressing altered hydrology is critical to fully recover natural ecosystem processes.

Integrating Topological and Hydraulic Attributes for Robustness Analysis of Water Distribution Networks

Researchers are recognizing that the robustness evaluation of Water Distribution Networks (WDNs) is of great importance for reducing the impact of disruptive events. Yet, very few methods to measure the robustness of WDNs have been developed. These methods mainly focus on either the topological features or the hydraulic attributes of WDNs and fail to provide a comprehensive picture of the robustness characteristics of WDNs. The work described herein proposes a new robustness index to measure the heterogeneity of WDNs drawing on informational entropy theory. The paper attempts to shift away from an exclusive topological viewpoint or a pure hydraulic approach, towards a combined topological and hydraulic analysis. The main emphasis is on the influence of an individual node on the overall network performance. The use of the proposed index is illustrated with a real-world WDN of an Australian town. The results highlight the significance of integrating the topological and hydraulic metrics for a reliable assessment of robustness in WDNs.

Can catchment-scale urban stormwater management measures benefit the stream hydraulic environment?

The potential for catchment-scale stormwater control measures (SCMs) to mitigate the impact of stormwater runoff issues and excess stormwater volume is increasingly recognised. There is, however, limited understanding about their potential in reducing in-channel disturbance and improving hydraulic conditions for stream ecosystem benefits. This study investigates the benefits that SCM application in a catchment have on in-stream hydraulics. To do this, a two-dimensional hydraulic model was employed to simulate the stream hydraulic response to scenarios of SCM application applied in an urban catchment to return towards pre-development hydrologic pulses. The hydraulic response analysis considered three hydraulic metrics associated with key components of stream ecosystem functions: benthic mobilization, hydraulic diversity and retentive habitat availability. The results showed that when applied intensively, the developed SCM scenarios could effectively restore the in-stream hydraulics to close to natural levels. Compared to an unmanaged urban case (no SCMs), SCM scenarios yielded channels with reduced bed mobility potential, close to natural hydraulic diversity and improvement of retentive habitat availability. This indicates that mitigating the effect of stormwater driven hydrological change could result in significant improvements in the physical environment to better support ecosystem functioning. We therefore suggest that intensive implementation of SCMs is an important action in an urbanizing catchment to maintain the flow regime and hydraulic conditions that sustain the ‘natural’ stream habitat functioning. We propose that stormwater management and protection of stream ecosystem processes should incorporate hydraulic metrics to measure the effectiveness of management strategies.

Restoring in‐stream habitat in urban catchments: Modify flow or the channel?

AbstractUrban streams have almost universally altered physical habitat conditions due to excess stormwater run‐off. This includes changes to in‐channel hydraulics and channel morphology. Restoration of in‐channel habitat has two main levers: address the hydrology or channel morphology. Both variables impact in‐stream habitat, but understanding the relative role of hydrologic and morphologic change remains a challenge. This study uses two‐dimensional hydraulic modelling to examine the relative roles of flow and channel morphology in setting hydraulic conditions. We investigated four test scenarios involving the combinations of urban versus natural hydrology and urban versus natural channel morphology. The analysis investigated three ecologically relevant hydraulics characteristics: bed mobilization, retentive habitat, and floodplain inundation, using Shields stress, shallow slow‐water habitat (SSWH) area, and floodplain inundation area hydraulic metrics, respectively. The results indicate substantial differences in hydraulic conditions between the two reaches. The urban reach showed increased bed mobility potential and SSWH availability plummeted as flow increased, whereas the natural channel showed a relatively stable bed with substantially more SSWH at most flows. Floodplain inundation frequency was low in the urban channel with decreased duration. Scenarios examined suggest that hydraulic conditions are highly sensitive to channel morphology relative to flow regime. This suggests that once channel form has been degraded, mitigating urbanization impacts on flow regime cannot maintain “natural” channel hydraulics. Management approaches therefore must protect channel morphology from change. Where the channel has already been fundamentally altered, opportunities for channel morphology rehabilitation need to be considered.

Effect of urbanization on stream hydraulics

AbstractUrbanization results in major changes to stream morphology and hydrology with the latter often cited as a primary stressor of urban stream ecosystems. These modifications unequivocally alter stream hydraulics, but little is known about such impacts. Hydraulic changes due to urbanization were demonstrated using two‐dimensional hydrodynamic model simulations, comparing urban and non‐urban stream reaches. We investigated three ecologically relevant hydraulic characteristics: bed mobilization, retentive habitat, and floodplain inundation, using hydraulic metrics bed shear stress, shallow slow‐water habitat (SSWH) area, and floodplain inundation area. We hypothesized that urbanization would substantially increase bed mobilization, decrease retentive habitat, and due to increased channel size would decrease floodplain inundation. Relative percent area of bed disturbance was 4 times higher, compared with that of the non‐urban stream at bankfull discharge. SSWH availability rapidly diminished in the urban stream as discharge increased, with SSWH area and patch size 2 times smaller than the non‐urban stream for a frequently occurring flow 0.7 times bankfull discharge. Floodplain inundation decreased in frequency and duration. These results demonstrate changes in hydraulics due to urbanization that may impact on physical habitat in streams. New “water sensitive” approaches to stormwater management could be enhanced by specification of hydraulic regimes capable of supporting healthy stream habitats. We propose that a complete management approach should include the goals of restoration and protection of natural hydraulic processes, particularly those that support ecological and geomorphic functioning of streams.

Modelling Whitewater Park Hydraulics and Fish Habitat in Colorado

AbstractWhitewater parks (WWPs) are increasingly popular recreational amenities, but the effects of WWPs on fish habitat and passage are poorly understood. This study investigated the use of a two‐dimensional (2‐D) model as compared with a three‐dimensional (3‐D) hydrodynamic model (flow‐3D®) for assessing effects of WWPs on fish habitat. The primary aims of this study were to (1) examine the utility of 3‐D modelling versus 2‐D modelling in a hydraulically complex WWP and (2) compare modelled habitat quality for resident fishes with actual fish abundance and biomass generated from field sampling surveys. Two reaches of a wadeable river in Colorado were modelled: a natural reach and a reach containing a WWP. A 2‐D habitat suitability analysis for juvenile and adult brown trout, juvenile and adult rainbow trout, longnose dace and longnose sucker predicted the same or higher habitat quality in the WWPs than the natural pools for all four species and for all modelled flow rates; however, results from fish sampling found significantly higher fish biomass for all four species in natural pools compared with WWP pools. All hydraulic metrics (depth, depth‐averaged velocity, turbulent kinetic energy, 2‐D and 3‐D vorticity) had higher magnitudes in WWP pools than in natural pools. In the WWP pools, 3‐D model results described the spatial distribution of flow characteristics or the magnitude of variables better than 2‐D results. This supports the use of 3‐D modelling for complex flows found in WWPs, but improved understanding of linkages between fish habitat quality and 3‐D hydraulic descriptors is needed. Copyright © 2015 John Wiley & Sons, Ltd.

An Evaluation of the Stream Simulation Culvert Design Method in Washington State

AbstractStream simulation has become an increasingly common culvert design method around the world. It is based on the assumption that geologic and hydraulic conditions in natural channels define passage characteristics for migrating fish and that water crossing structures that imitate these conditions can then achieve those same passage characteristics. This study expands on an initial evaluation of 19 culverts in 2003 to 50 culverts and includes methods and analyses comparing hydraulic characteristics based on cross sections, profile variation, and bed texture between each culvert and its paired reference reach situated in an adjacent section of the natural channel of each stream. Taken as a group, these culverts simulate bed texture, 100‐year recurrence interval flood velocity and 2‐year flood width but did not simulate thalweg complexity or other hydraulic metrics. Culvert span, relative to the bankfull width of the stream, does not by itself determine whether the culvert simulates the reference reach. Of the 50 culverts, many of which experienced record floods, only one showed significant bed degradation. Copyright © 2014 John Wiley & Sons, Ltd.

Hydrologic indicators of hydraulic conditions that drive flow–biota relationships

This article tests the association between streamflow alteration and the alteration of ecologically significant hydraulic environments. There has been a recent shift in environmental flow assessments to develop rapid desktop-based approaches that are applicable in a regional context. Streamflow statistics (e.g. minimum monthly flow) are often chosen to predict the impact of streamflow alteration on aquatic ecosystems. The assumption that the flow–biota relationship will be obscured by the effect of how streamflow interacts with channel morphology is often acknowledged, but not quantified. In this study, streamflow statistics are derived for 19 reaches in four river systems in Victoria, Australia. Hydraulic metrics were used to quantify ecologically significant surface flow conditions (Froude number) and the area of bench inundation, shallow and deep water. Multivariate analysis was used to investigate the correlation between streamflow statistics altered with regulation and the hydraulic metrics. It was found that streamflow statistics have a weak correlation to surface flow condition and the area of shallow water under natural streamflow conditions. The results show that hydrologic statistics have limited utility in quantifying changes in hydraulic environments. A similar magnitude of flow alteration can produce diverse hydraulic results. The confounding influence of channel morphology prevents streamflow statistics being an adequate surrogate for the assessment of hydraulic alteration. Modelling flow–biota relationships in a regional context is limited by the inadequacy of streamflow statistics to model ecologically significant hydraulic function. Improving knowledge of ecohydraulically significant hydrologic statistics will improve the effectiveness of environmental flow planning to sustain instream habitat conditions. A probabilistic approach is required to enable a risk-based approach to desktop generalization of flow–biota relations.Editor Z.W. Kundzewicz; Guest editor M. AcremanCitation Turner, M. and Stewardson, M., 2014. Hydrologic indicators of hydraulic conditions that drive flow–biota relationships. Hydrological Sciences Journal, 59 (3–4), 659–672.

A high‐resolution hydrodynamic investigation of brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) redds

AbstractHigh‐resolution velocity measurements were taken over a series of redds on a gravel‐bed stream using a Pulse Coherent Acoustic Doppler Profiler (PCADP) to quantify the hydrodynamics of brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) redds. On redds studied, over 4500 velocity measurements per redd were acquired per day to quantify the flow velocity, flow depth and related fluid mechanics metrics of Reynolds numbers, Froude numbers and turbulent kinetic energy per unit area. Results showed that velocity and Froude numbers varied widely at the redd scale, but consistently showed higher velocities and Froude numbers over the tailspill regions relative to the surrounding study limits. Results of Reynolds numbers calculations showed no apparent correlations to spawning location preference and redd structure. Turbulent kinetic energy per unit area consistently demonstrated a strong correlation with redd locations. The metric maintained low values (i.e. unidirectional flow with little turbulence) where all redds and attempted redds were observed. The study also demonstrates that a number of hydraulic metrics and several spatial scales will likely be necessary to understand any inherent relationship between river hydraulics and redd placement. Copyright © 2010 John Wiley & Sons, Ltd.

Relationship of stream ecological conditions to simulated hydraulic metrics across a gradient of basin urbanization

The relationships among urbanization, stream hydraulics, and aquatic biology were investigated across a gradient of urbanization in 30 small basins in eastern Wisconsin, USA. Simulation of hydraulic metrics with 1-dimensional unsteady flow models was an effective means for mechanistically coupling the effects of urbanization with stream ecological conditions (i.e., algae, invertebrates, and fish). Urbanization, characterized by household, road, and urban land density, was positively correlated with the lowest shear stress for 2 adjacent transects in a reach for the low-flow summer (p < 0.001) and autumn (p < 0.01) periods. Urbanization also was positively correlated with Reynolds number and % exposed stream bed during months with moderate to low flows. Our study demonstrated the value of temporally and spatially explicit hydraulic models for providing mechanistic insight into the relationships between hydraulic variables and biological responses. For example, the positive correlation between filter-feeding invertebrate richness and minimum 2-transect shear stress observed in our study is consistent with a higher concentration of water-column particulates available for filtration. The strength of correlations between hydraulic and biological metrics is related to the time period (annual, seasonal, or monthly) considered. The hydraulic modeling approach, whether based on hourly or daily flow data, allowed documentation of the effects of a spatially variable response within a reach, and the results suggest that stream response to urbanization varies with hydraulic habitat type.

Applying spatial hydraulic principles to quantify stream habitat

AbstractFlow complexity plays an important role in stream ecology. Yet, a paucity of research exists with regard to quantifying flow complexity and relating it to the habitats that aquatic organisms utilize. Here we provide a generalized example of how two‐dimensional (2‐D) numerical hydraulic models and spatial hydraulic metrics can be used to simulate and quantify biologically important flow patterns within streams. A detailed topographic survey, incorporating meso‐scale topographic features (e.g. exposed boulders and bedrock outcrops) is performed for a small urbanized stream. The 2‐D hydraulic model RMA2 is then used to model the flow conditions within the stream reach. Model results demonstrate that the meso‐scale topographic features create highly complex flow patterns of potential biological importance. Recently developed spatial hydraulic metrics, based on hydraulic engineering principles (vorticity, circulation and kinetic energy gradients), are then used to quantify the various types of flow complexity found within the stream reach. In particular, spatial hydraulic metrics are used to quantify the stream reach's overall flow complexity and the flow complexity surrounding three chub mounds. A method for uniquely characterizing circulation zones is then developed and applied to five circulation zones within the study reach. The principles used in performing this study's topographic survey, spatial explicit hydraulic modelling and spatial hydraulic analyses, form a general framework for quantifying flow complexity in any stream. The ways in which using hydraulic models and spatial hydraulic metrics can help establish better habitat suitability criteria and design best management practices for use in stream and catchment area restoration projects is discussed. Copyright © 2005 John Wiley &amp; Sons, Ltd.

Vorticity and circulation: spatial metrics for evaluating flow complexity in stream habitats

Channel topography, formed by boulders, submerged bars, and meanders, creates complex flow patterns. These flow patterns exist over a variety of spatial scales and provide habitat for many aquatic organisms. Spatial flow features cannot be adequately characterized with qualitative descriptions or hydraulic metrics such as depth and velocity. Two-dimensional hydraulic model simulations, based on detailed channel geometry, are used to develop and test vorticity (a point metric) and a circulation-based metric (an area metric) as means of quantifying spatial flows occurring within micro-, meso-, and macro-habitat features. The proposed spatial metrics are computed throughout distinctly different regions of a study site. The vorticity metric produces small absolute values in uniform flows and large absolute values in complex flows. Circulation metric values varied by a factor of 11.7 within distinctly different regions of the modeled study site and suggest that the metric provides a means of quantifying flow complexity within a study reach or within individual mesoscale habitats such as pools, eddies, riffles, and transverse flows. The circulation metric is used to quantify flow complexity around three brown trout (Salmo trutta) redds to provide an example of how the proposed metric might be employed in habitat studies.