Catchment Processes Research Articles

Catchment properties, function, and conceptual model representation: is there a correspondence?

AbstractThis study investigates the possible correspondence between catchment structure, as represented by perceptual hydrological models developed from fieldwork investigations, and mathematical model structures, selected on the basis of reproducing observed catchment hydrographs. Three Luxembourgish headwater catchments are considered, where previous fieldwork suggested distinct flow‐generating mechanisms and hydrological dynamics. A set of lumped conceptual model structures are hypothesized and implemented using the SUPERFLEX framework. Following parameter calibration, the model performance is examined in terms of predictive accuracy, quantification of uncertainty, and the ability to reproduce the flow–duration curve signature. Our key research question is whether differences in the performance of the conceptual model structures can be interpreted based on the dominant catchment processes suggested from fieldwork investigations. For example, we propose that the permeable bedrock and the presence of multiple aquifers in the Huewelerbach catchment may explain the superior performance of model structures with storage elements connected in parallel. Conversely, model structures with serial connections perform better in the Weierbach and Wollefsbach catchments, which are characterized by impermeable bedrock and dominated by lateral flow. The presence of threshold dynamics in the Weierbach and Wollefsbach catchments may favour nonlinear models, while the smoother dynamics of the larger Huewelerbach catchment were suitably reproduced by linear models. It is also shown how hydrologically distinct processes can be effectively described by the same mathematical model components. Major research questions are reviewed, including the correspondence between hydrological processes at different levels of scale and how best to synthesize the experimentalist's and modeller's perspectives. Copyright © 2013 John Wiley & Sons, Ltd.

Flood-initiating catchment conditions: a spatio-temporal analysis of large-scale soil moisture patterns in the Elbe River basin

Abstract. Floods are the result of a complex interaction between meteorological event characteristics and pre-event catchment conditions. While the large-scale meteorological conditions have been classified and successfully linked to floods, this is lacking for the large-scale pre-event catchment conditions. Therefore, we propose classifying soil moisture as a key variable of pre-event catchment conditions and investigating the link between soil moisture patterns and flood occurrence in the Elbe River basin. Soil moisture is simulated using a semi-distributed conceptual rainfall-runoff model over the period 1951–2003. Principal component analysis (PCA) and cluster analysis are applied successively to identify days of similar soil moisture patterns. The results show that PCA considerably reduced the dimensionality of the soil moisture data. The first principal component (PC) explains 75.71% of the soil moisture variability and represents the large-scale seasonal wetting and drying. The successive PCs express spatially heterogeneous catchment processes. By clustering the leading PCs, we identify large-scale soil moisture patterns which frequently occur before the onset of floods. In winter, floods are initiated by overall high soil moisture content, whereas in summer the flood-initiating soil moisture patterns are diverse and less stable in time.

The relative influences of climate and catchment processes on Holocene lake development in glaciated regions

Following deglaciation, the long-term pattern of change in diatom communities and the inferred history of the aquatic environment are affected by a hierarchy of environmental controls. These include direct climate impacts on a lake’s thermal and hydrologic budgets, as well as the indirect affects of climate on catchment processes, such as weathering, soil development, microbial activity, fire, and vegetation composition and productivity, which affect the transfer of solutes and particulates from the terrestrial ecosystem into the lake. Some of these catchment influences on lacustrine systems operate as time-dependent patterns of primary succession that are set in motion by glacier retreat. This paper provides a conceptual model of some dominant pathways of catchment influence on long-term lake development in glaciated regions and uses a series of paleolimnological examples from arctic, boreal, and temperate regions to evaluate the relative role of direct climate influences and of catchment processes in affecting the trajectory of aquatic ecosystems during the Holocene in different environmental contexts.

Safeguarding the provision of ecosystem services in catchment systems

A narrow technocentric focus on a few favored ecosystem services (generally provisioning services) has led to ecosystem degradation globally, including catchment systems and their capacities to support human well-being. Increasing recognition of the multiple benefits provided by ecosystems is slowly being translated into policy and some areas of practice, although there remains a significant shortfall in the incorporation of a systemic perspective into operation management and decision-making tools. Nevertheless, a range of ecosystem-based solutions to issues as diverse as flooding and green space provision in the urban environment offers hope for improving habitat and optimization of beneficial services. The value of catchment ecosystem processes and their associated services is also being increasingly recognized and internalized by the water industry, improving water quality and quantity through catchment land management rather than at greater expense in the treatment costs of contaminated water abstracted lower in catchments. Parallel recognition of the value of working with natural processes, rather than "defending" built assets when catchment hydrology is adversely affected by unsympathetic upstream development, is being progressively incorporated into flood risk management policy. This focus on wider catchment processes also yields a range of cobenefits for fishery, wildlife, amenity, flood risk, and other interests, which may be optimized if multiple stakeholders and their diverse value systems are included in decision-making processes. Ecosystem services, particularly implemented as a central element of the ecosystem approach, provide an integrated framework for building in these different perspectives and values, many of them formerly excluded, into commercial and resource management decision-making processes, thereby making tractable the integrative aspirations of sustainable development. This can help redress deeply entrenched inherited assumptions, habits, and vested interests, replacing them in many management situations with wider recognition of the multiple values of ecosystems and their services. Global interest in taking an ecosystem approach is promoting novel scientific and policy thinking, yet there is a shortfall in its translation into practical management tools. Professional associations may have key roles to play in breaking down barriers to the "mainstreaming" of systemic perspectives into common practice, particularly through joining u different sectors of society essential to their implementation and ongoing adaptive management.

Changes in catchment conditions lead to enhanced remobilization of arsenic in a water reservoir

Increasing arsenic concentrations in freshwater ecosystems is of global concern. Processes affecting arsenic fluxes in catchments are known. These processes are in turn controlled by the underlying geology and air pollution history. In contrast to the knowledge on catchment processes less is known about the hydrochemical processes controlling the fixation/remobilization of arsenic within lakes and artificial reservoirs. Consequently, we examined a reservoir system in the Ore Mts. (Germany) regarding its sink and source potentials affecting arsenic fluxes. This area was faced with heavy deposition inputs from coal burning based acid rain until the beginning of the 1990s. Hereafter concentrations of sulfate and nitrate in runoff waters decreased, whereas dissolved organic carbon (DOC) concentrations are still increasing. Along with this, arsenic concentrations in the water discharge from the catchments increase. Our results reveal that the sediments of the investigated reservoir system contain high inventories of arsenic in association with ferric and organic phases. A nitrate deficit dependent arsenic release is suggested. It is indicated that arsenic release from the reservoir sediments may be controlled by water nitrate concentration, which in turn is dependent on the nitrate concentration in the runoff water from the catchment.

Catchments in the future North: interdisciplinary science for sustainable management in the 21st Century

Catchments in the future North: interdisciplinary science for sustainable management in the 21^st Century

An approach to identify time consistent model parameters: sub-period calibration

Abstract. Conceptual hydrological models rely on calibration for the identification of their parameters. As these models are typically designed to reflect real catchment processes, a key objective of an appropriate calibration strategy is the determination of parameter sets that reflect a "realistic" model behavior. Previous studies have shown that parameter estimates for different calibration periods can be significantly different. This questions model transposability in time, which is one of the key conditions for the set-up of a "realistic" model. This paper presents a new approach that selects parameter sets that provide a consistent model performance in time. The approach consists of testing model performance in different periods, and selecting parameter sets that are as close as possible to the optimum of each individual sub-period. While aiding model calibration, the approach is also useful as a diagnostic tool, illustrating tradeoffs in the identification of time-consistent parameter sets. The approach is applied to a case study in Luxembourg using the HyMod hydrological model as an example.

Development of Water Management Modeling by using GIS in Chirchik River Basin, Uzbekistan

The management of water resources has become a critical need for Chirchik river basin in Uzbekistan due to water deficit and salt damage. Hence, plans must be developed for water efficient use through better management at the river basin level. In this paper, fundamental concept of the proposed water management modeling of the Chirchik river basin and overview of hydrological model using Geomorphology Based Hydrological Model (GBHM). Furthermore, various spatial data such as land-use layers and hydrological layers are developed in this study by conducting latest GIS (Geographical Information System) technology. By extracting ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) Digital Elevation Model (DEM) and ALOS (Advanced Land Observing Satellite) data on autumn and spring, a series of land-use classification is created using the supervised classification method. For regional-scale hydrological modeling, GBHM as a powerful tool is used to analyze the river basin by utilizing the geomorphological properties data for each catchment and hillslope hydrological processes. As a result, development of spatial modeling is obtained and GIS-based analysis is an effective method to study water management in Chirchik river basin in Uzbekistan.

Steady infiltration rates estimated for a mountain forest catchment based on the distribution of plant species

Among other important factors, vegetation cover strongly affects the hydrological processes in mountain catchments. In this paper, we present the results of field infiltration measurements at the location of various vegetation covers, together with an estimation of the infiltration characteristics of a small mountain forest catchment. Measured steady infiltration rate values were extrapolated on the basis of the dominant plant species distribution in the catchment. We determined which plant species are dominant, and infiltration tests were carried out where these species were located in selected sites in the catchment. The characteristic steady infiltration rates were averaged for each dominant vegetation species. The percentages of dominant plant species were determined for established points placed in a regular network throughout the basin. An extrapolation of the directly measured infiltration values to these established points was calculated using (1) percentages of the dominant plant species determined at these points, and (2) characteristic infiltration rates averaged for these species. An infiltration map was created from the infiltration values calculated for the established points.

SWAT model calibration of a grid-based setup

Abstract. The eco-hydrological model SWAT (Soil and Water Assessment Tool) is a useful tool to simulate the effects of catchment processes and water management practices on the water cycle. For each catchment some model parameters (e.g. ground water delay time, ground water level) remain constant and therefore are used as constant values; other parameters such as soil types or land use are spatially variable and thus have to be spatially discretized. SWAT setup interfaces process input data to fit the data format requirements and to discretize the spatial characteristics of the catchment area. The primarily used configuration is the sub-watershed discretization scheme. This spatial setup method, however, results in a loss of spatial information which can be problematic for SWAT applications that require a spatially detailed description of the catchment area. At present no SWAT interface is available which provides the management of input and output data based on grid cells. To fill this gap, the authors developed a grid-based model interface. To perform hydrological studies, the SWAT user first calibrates the model to fit to the environmental and hydrological conditions of the catchment. Compared to the sub-watershed approach, the grid-based setup significantly increases model computation time and hence aggravates calibration according to established calibration guidelines. This paper describes how a conventional set of sub-watershed SWAT parameters can be used to calibrate the corresponding grid-based model. The procedure was evaluated in a sub-catchment of the River Elbe (Northern Germany). The simulation of daily discharge resulted in Nash-Sutcliffe efficiencies ranging from 0.76 to 0.78 and from 0.61 to 0.65 for the calibration and validation period respectively; thus model performance is satisfactory. The sub-watershed and grid configuration simulate comparable discharges at the catchment outlet (R2 = 0.99). Nevertheless, the major advantage of the grid-based set-up is an enhanced spatial description of landscape units inducing a more realistic spatial distribution of model output parameters.

Use of gaseous tracers (CFCs and SF6) and transit-time distribution spectrum to validate a shallow groundwater transport model

► Pertinent data for validation of catchment solute-transport models are lacking. ► Interests of gaseous tracers and spectrum of transit time distribution are analysed. ► Transit time distribution spectrum is a very relevant validation variable. Catchment-scale solute transport models constitute potentially powerful tools of water resources management for predicting the evolution of water quality in response to land use modifications. Validation of the models remains a crucial step in order to get reliable prediction. However, pertinent data for the validation step are lacking. When catchment solute transport models are applied to shallow groundwater catchments, catchment-scale model validation relies on the validation of the groundwater solute transport model. Here we studied the interests of two approaches for groundwater solute transport model validation: the use of (i) gaseous atmospheric tracers and (ii) of spectral properties of transit time distributions derived from tracer concentration time series of rainfall and stream base-flow. The Kervidy-Naizin catchment, a 5 km 2 catchment in Western France was chosen as case application. Three simulations with a shallow groundwater transport model were performed using three sets of effective porosity, respectively. We then investigated the ability of four gaseous tracers (CFC-11, CFC-12, CFC-113 and SF 6 ) and transit time distribution spectra to identify the most realistic simulations. The three simulations led to mean transit times that varied over a wide range of values, from 1.2 to 12.1 yr. Simulated groundwater mixing ratio differences for the three simulations did not exceed 5% for CFC-11, regardless of the groundwater location. The values of the SF 6 , CFC-12 and CFC-113 mixing ratio differences between the two simulations that contained the two shortest mean transit times were within expected measurement error of the tracer concentrations, regardless of the groundwater location. In contrast, the mixing ratio differences between the two simulations with the shortest mean transit times and the simulation containing the largest one exceeded 28% at all groundwater locations for SF 6 and 9% in groundwater discharging into the stream for CFC-12 and CFC-113. The spectra of the three simulated transit time distributions do not match the transit time distribution spectrum derived from chloride concentration time series. So these results show that transit time distribution spectrum, and in much less extend SF 6 , CFC-12 and CFC-113 mixing ratios are sensitive enough to effective porosity values to be used as validation variables in shallow groundwater transport modelling. Transit time distribution spectrum constitutes an integrative variable able to discriminate between shallow groundwater transport simulations leading to very close mean transit times. In the present work, the discrepancy between the simulated spectra and the spectrum derived from the chloride concentration may come from other catchment processes than groundwater transport process, or from a wrong modelling of the groundwater transport process. Globally, deriving reliable transit time distribution spectrum requires high-frequency and extensive time series of a conservative tracer measured in stream water and rainfall, which is not straightforward to collect. The low sensitivity of simulated CFC-11 tracer mixing ratios to simulated groundwater transit times, and thus to model parameters, constituted a shortcoming to use it as a validation variable of groundwater solute transport models.

What controls the spatial patterns of the riverine carbonate system? — A case study for North America

In this study we analyzed the large scale spatial patterns of river pH, alkalinity, and CO2 partial pressure (PCO2) in North America and their relation to river catchment properties. The goal was to set up empirical equations which can predict these hydrochemical properties for non-monitored river stretches from geodata of e.g. terrain attributes, lithology, soils, land cover and climate.For an extensive dataset of 1120 river water sampling locations average values of river water pH, alkalinity and PCO2 were calculated. The catchment boundaries and catchment properties were calculated using GIS and different sets of geodata. The correlations between the hydrochemical properties and the catchment properties were explored using simple and multiple linear regression analysis.For each of the considered hydrochemical parameters, a multiple regression equation was fitted: for pH with the predictor's mean annual precipitation and areal proportions of carbonate rocks (r2=0.60); for alkalinity, in addition to these two predictors, with subsoil pH and areal proportions agricultural lands (r2=0.66); and for pPCO2 (i.e. the negative logarithm of PCO2) with mean air temperature, mean catchment slope gradient, and mean annual precipitation (r2=0.43). Based on these results, we argue that spatial patterns in river water pH and alkalinity are governed by catchment processes related to chemical rock weathering. For the PCO2, on the other hand, the spatial patterns are governed by in-river processes on which catchment properties can have an indirect effect. We conclude that our approach can be used to predict averages of these parameters for non-monitored river stretches, which in-turn allows for a better spatially explicit representation of the rivers' carbonate system at the regional to global scale, which will be needed for a refined analysis of rivers in the global carbon cycle.

On the testing of fully integrated surface–subsurface hydrological models

AbstractStudies employing integrated surface–subsurface hydrological models (ISSHMs) have utilized a variety of test cases to demonstrate model accuracy and consistency between codes. Here, we review the current state of ISSHM testing and evaluate the most popular ISSHM test cases by comparing the hydrodynamic processes simulated in each case to the processes found in well‐characterized, real‐world catchments and by comparing their general attributes to those of successful benchmark problems from other fields of hydrogeology. The review reveals that (1) ISSHM testing and intercode comparison have not adopted specific test cases consistently; (2) despite the wide range of ISSHM metrics available for model testing, only two model performance diagnostics are typically adopted: the catchment outflow hydrograph and the catchment water balance; (3) in intercode comparisons, model performance is usually judged by evaluating only one performance diagnostic: the catchment outflow hydrograph; and (4) ISSHM test cases evaluate a small number of hydrodynamic processes that are largely uniform across the model domain, representing a limited selection of the processes of interest in well‐characterized, real‐world catchments. ISSHM testing would benefit from more intercode comparisons using a consistent set of test cases, aimed at evaluating more catchment processes (e.g. flooding) and using a wider range of simulation diagnostics (e.g. pressure head distributions). To achieve this, a suite of test case variations is required to capture the relevant catchment processes. Finally, there is a need for additional ISSHM test problems that compare model predictions with hydrological observations from intensively monitored field sites and controlled laboratory experiments. Copyright © 2012 John Wiley & Sons, Ltd.

Cross‐regional prediction of long‐term trajectory of stream water DOC response to climate change

There is no scientific consensus about how dissolved organic carbon (DOC) in surface waters is regulated. Here we combine recent literature data from 49 catchments with detailed stream and catchment process information from nine well established research catchments at mid‐ to high latitudes to examine the question of how climate controls stream water DOC. We show for the first time that mean annual temperature (MAT) in the range from −3° to +10° C has a strong control over the regional stream water DOC concentration in catchments, with highest concentrations in areas ranging between 0° and +3° C MAT. Although relatively large deviations from this model occur for individual streams, catchment topography appears to explain much of this divergence. These findings suggest that the long‐term trajectory of stream water DOC response to climate change may be more predictable than previously thought.

Understanding the characteristics of a groundwater-dependent ecosystem: Eucalyptus parramattensis Woodland at Porters Creek Wetland, NSW.

Little is known about groundwater-dependent ecosystems in south-eastern Australia and few studies have examined the impact of landclearing upslope of such ecosystems. The eastern edge of Porters Creek wetland, near Warnervale on the Central Coast of New South Wales, supports a Eucalyptus parramattensis subsp. Parramattensis (Parramatta Red Gum) population. The population has been listed as an Endangered Population (EP) and was showing signs of dieback during the 2002 to mid-2007 drought. Water table depth, soil moisture tension, soil temperature and groundwater salinity beneath this woodland were measured to investigate whether the woodland is associated with a shallow aquifer and/or high soil moisture conditions, and whether an upslope construction development would impact on the ecosystem. The composition, structure and health of the Eucalyptus parramattensis Woodland was also examined. Monitoring over 5 years demonstrated that Eucalyptus parramattensis is associated with a shallow, slightly saline to saline (8–12 ppt) water table, 1.4–3.1 m beneath the surface of a drainage depression wetland. During the drought water table drawdown rates were quite rapid, and rainfall events took up to a month to replenish water table levels. Landclearing for an upslope development significantly decreased the average water table level by 0.3–0.5 m during the construction phase, while peaks that occurred at the base of the slope after large rainfall events reversed the normal direction of the water table gradient. The water table re-stabilised to pre-construction levels after construction was completed and the area was landscaped and revegetated with grass. The short-term alteration of groundwater conditions did not appear to impact on tree health; the poor tree health observed prior to construction was most likely due to the lowering of the water table (and/or an increase in groundwater/soil salinity) during the drought years. Our results suggest that developments that revegetate slopes above wetlands as quickly as possible after clearing, orundertake clearing in stages, will minimise effects on water table levels. Pervious detention basins designed to capture runoff and allow infiltration into the soil help replenish aquifers, but also require weed maintenance. This study highlights the significance of maintaining shallow aquifer and catchment processes for the conservation and rehabilitation of coastal wetlands, many of which are listed as Endangered Populations or Endangered Ecological Communities.

The application of fallout radionuclides to determine the dominant erosion process in water supply catchments of subtropical South‐east Queensland, Australia

AbstractPrevious studies using fallout radionuclides (137Cs and 210Pbex) to determine the relative contributions of surface‐soil and channel erosion (including gullies and channel banks) to stream sediments have used a relatively small number of composite samples (<25) to characterize the source end members, and concentrations in each of the source end members have, through the use of means and standard errors, been assumed to be normally distributed. Here, we examine 137Cs activity concentrations to determine the erosion processes supplying sediment in seven water supply catchments in South‐east Queensland. First, we test some of the underlying assumptions in the method using concentrations of 137Cs and 210Pbex in composite samples collected from 109 surface‐soil sites and 39 channel‐bank sites. Paired composite samples, each consisting of 20 subsamples, from five sites are used to demonstrate that this sampling approach was sufficient to average out any local variations in surface‐soil 210Pbex and 137Cs concentrations across the 300 m2 sampled. We derive probability distributions for 137Cs and 210Pbex concentrations in the group of samples from each of the end members and show that only the distribution of 210Pbex in samples from surface soils is normally distributed. We use the probability distributions for 137Cs, which provides the greatest discrimination between sources, to show that the 137Cs concentrations on the river sediment samples are consistent with channel erosion being the dominant source. Conservation works aimed at reducing the supply of sediments in these catchments should therefore focus on rehabilitation of the channel network and decreasing the runoff to the channel network. These findings are consistent with other similar studies on tropical Australian rivers. Copyright © 2012 John Wiley & Sons, Ltd.

Spatial and temporal soil moisture estimation from RADARSAT-2 imagery over Flevoland, The Netherlands

► Assess the ability of RADARSAT-2 for soil moisture retrieval over Flevoland. ► Evaluate both spatial and temporal soil moisture retrieval techniques. ► Circumvent surface roughness field measurements. ► Spatial and temporal retrievals have accuracy around 4 vol% for medium rough soils. ► Temporal retrieval performs better for smoother fields covered by stubbles. Both spatial and temporal soil moisture dynamics have a large impact on hydrologic processes in agricultural catchments. As acquiring ground measurements of soil moisture is labor intensive, it is often limited in space (to a few locations) and time (to a small number of campaigns). Remote sensing offers a useful alternative, as it allows for observing both across time and space. This study analyses the potential to retrieve spatial and temporal soil moisture information from a series of RADARSAT-2 HH- and VV-polarized C-band (5.405 GHz) backscatter observations over a large number of (nearly) bare soil agricultural fields in Flevoland, The Netherlands, acquired in the framework of AgriSAR 2009. The RADARSAT-2 backscatter observations are found to be strongly correlated with continuous soil moisture measurements recorded at two agricultural sites during the 2009 growing season, as well as with spatial soil moisture measurements conducted during three intensive field campaigns in August and September 2009. Furthermore, two different soil moisture retrieval approaches have been evaluated: a physically-based modeling approach and change detection technique. The physically-based approach makes use of the Integral Equation Model with input of effective surface roughness parameters that are updated every acquisition for each field. The soil moisture retrieval accuracy of this technique is calculated based on leave-one-out cross-validation, yielding an accuracy (RMSE) about 4 vol% for fields with medium surface roughness at both polarization schemes. For smoother fields covered by stubbles, the retrieval accuracy slightly deteriorates. The change detection technique relies on a normalization of the backscatter between dry and wet reference soil moisture measurements, yielding accuracies about 4 vol% both for fields characterized by medium roughness and stubble conditions. This study confirms the large potential of RADARSAT-2 data for the retrieval of spatial and temporal soil moisture dynamics.

Flood timescales: Understanding the interplay of climate and catchment processes through comparative hydrology

We analyze the controls on flood duration based on the concept of comparative hydrology. Rather than modeling a single catchment in detail, we compare catchments with contrasting characteristics in order to understand the controls in a holistic way. We analyze the hydrographs of 9223 maximum annual flood events in 396 Austrian catchments ranging from 5 to ∼10,000 km2 as a function of climatic controls such as storm type (synoptic and convective storms, rain‐on‐snow, snowmelt), and catchment controls such as soils, soil moisture, geology, and land form. The ratio of the flood volume and the flood peak is used as a measure of the flood duration or flood timescale. The results indicate that, spatially, the median flood timescales range from 16 h in the hilly catchments, where convective storms prevail, to 104 h in the lowland catchments where substantial inundation into the floodplain occurs. The range is even larger for different flood types, from 7 h for flash floods in the hilly catchments to 200 h for snowmelt floods in an Alpine area with deeply weathered rocks and deep soils. The results also indicate that the catchment area is not the most important control on the flood timescales. For the range of catchments considered here, climate is very important through storm type and antecedent soil moisture, and geology is very important through soil characteristics. The concept of comparative hydrology is also used to interpret the interplay of the processes controlling the flood duration at timescales from hours to millennia. It is argued that the flood timescale is a rich fingerprint of the hydrological processes in a catchment because it integrates a range of climate and catchment characteristics by a time parameter.

Range of variability of channel complexity in urban, restored and forested reference streams

Summary 1. Channel complexity is an important ecological property of stream systems and is often targeted for restoration in channelised urban streams. However, channel complexity is rarely defined explicitly, and little research on channel complexity has been conducted in streams in urban catchments that have not been directly channelised by human activities. Therefore, it remains unclear whether restoration of non‐channelised urban streams has improved complexity.2. We explicitly define channel complexity and use a multimetric approach to provide a comprehensive assessment of complexity in multiple restored, urban and forested streams on the Maryland Coastal Plain and two streams of differing land use in Colorado. We also expand on the Maryland and Colorado results with a literature survey of channel complexity from diverse geographical regions.3. Many streams draining urban catchments in Maryland had relatively high values of some complexity metrics compared to forested reference streams in Maryland and compared to the values for pristine streams calculated from the literature. This suggests that streams in urban catchments that are not directly manipulated by human activities (e.g. channelisation or piping) may be able to maintain channel structures beneficial for aquatic organisms even when impervious surfaces are the dominant form of land use in the catchment.4. Restored streams in Maryland had equal or lower values of many complexity metrics compared to streams draining urban catchments in Maryland. This suggests that restoration of streams draining urban catchments did not improve the overall channel complexity.5. Our results highlight the need to explicitly define and measure the attributes of channel complexity that are targeted during restoration, to determine whether the streams in urban catchments are truly degraded with respect to channel complexity.6. Combined with recent synthesis work suggesting that biodiversity may not be improved by increasing the channel complexity, these results indicate that targeting catchment processes may prove a more useful approach to restoration than attempting to move channel complexity in streams draining urban catchments towards conditions in forested reference streams.

Distributed Hydrologic Modeling in the Suburban Landscape: Assessing Parameter Transferability from Gauged Reference Catchments1

Mittman, Tamara, Lawrence E. Band, Taehee Hwang, and Monica Lipscomb Smith, 2012. Distributed Hydrologic Modeling in the Suburban Landscape: Assessing Parameter Transferability from Gauged Reference Catchments. Journal of the American Water Resources Association (JAWRA) 48(3): 546‐557. DOI: 10.1111/j.1752‐1688.2011.00636.xAbstract: Distributed, process‐based models of catchment hydrologic response are potentially useful tools for the assessment of Low Impact Development (LID) techniques in urbanized catchments. Their application is often limited, however, by the lack of continuous streamflow records to calibrate poorly constrained parameters. This article examines the transferability of soil and groundwater parameters from a forested reference catchment to a nearby suburban catchment. We use the Regional Hydro‐Ecologic Simulation System (RHESSys) to develop hydrologic models of one gauged forested and one ungauged suburban catchment within the Baltimore Ecosystem Study (BES) study area. We use a parameter uncertainty framework to calibrate soil and groundwater parameters for the forested catchment, and discrete measurements of streamflow from the suburban catchment to assess parameter transferability. Results indicate that the transfer of soil and groundwater parameters from forested reference to nearby suburban catchments is viable, with performance measures for the suburban catchment often exceeding those for the forested catchment. We propose that the simplification of hydrologic processes in urbanized catchments may account for the increase in model performance in the suburban catchment.