Dynamic flow modelling of riverine amphibian habitat with application to regulated flow management

In regulated rivers, relicensing of hydropower projects can provide an opportunity to change flow regimes and reduce negative effects on sensitive aquatic biota. The volume of flow, timing and ramping rate of spring spills, and magnitude of aseasonal pulsed flows have potentially negative effects on the early life stages of amphibians, such as the Foothill yellow‐legged frog (Rana boylii). Two‐dimensional hydrodynamic modeling is one method to evaluate potential effects of flow variation on frog egg masses and tadpoles. We explored the usefulness of this technique by modeling habitat suitability under several pulsed flow scenarios in two river reaches in northern California, USA. We conducted analyses beyond simple weighted usable area calculations, such as quantifying the risk of scour or stranding, in order to quantify potential loss under different flow scenarios. The modeling results provided information on potential susceptibility to flow fluctuations as well as the influence of channel morphology on habitat suitability. Under each flow scenario, low percentages of suitable habitat remained suitable or were ‘buffered’ from the pulse, creating high potential for scour of egg masses or tadpoles. However, due to differences in channel morphologies, the wide, shallow study site provided 2‐3 times the buffering capacity of the entrenched study site. Additional analyses suggested that limited buffering capacity and lack of connectivity between suitable egg mass and tadpole habitats may explain why some hydraulically suitable habitats are unoccupied. This type of model‐based analysis would be useful for managing foothill yellow‐legged frogs or similar aquatic species in regulated river systems. Copyright © 2010 John Wiley & Sons, Ltd.     

Evaluation of the Missouri River shallow water habitat using a 2D‐hydrodynamic model

Many of the Upper Missouri River dikes have been notched to create additional shallow water habitat (SWH, operationally defined as areas in the stream with depth < 1.5 m, and velocity < 0.75 m s^?1) for fish populations. The goal of this study was to quantify the additional SWH gained from notching these dikes and to evaluate their performance under different flow conditions. A coupled field and numerical study was performed on a reach of the Missouri River, near Nebraska City, NE, which contains a number of dikes notched in 2004. The numerical simulations showed that the SWH criterion for depth was more difficult to satisfy in the study reach than the SWH criterion for velocity. Notching the dikes resulted in a slight shift of the bankline due to local erosion in the vicinity of the dikes and the formation of scour holes downstream of the notches. Results from the study suggested that notching the dikes had limited impact on the SWH because the area gained from the bankline shift was offset by the area lost from the scour holes formation. The performance of the notched dikes in sustaining the minimum habitat suitability conditions for the Missouri River ecosystem was also investigated. These conditions corresponded to discharges < 709 m³ s^?1 for the period from mid‐July to mid‐August, or equivalently SWH areas > 5225 m² dike^?1 during the same period. Analysis of the Missouri River annual discharge records at the study site showed that the dikes can provide the minimum required SWH for mean annual discharges < 667 m³ s^?1. For mean annual discharges > 667 m³ s^?1, new alternative structures or restoration facilities were needed, in addition to the existing dikes, to sustain the minimum required SWH. The dikes were not effective in providing any SWH for mean annual discharges > 2000 m³ s^?1. Copyright © 2010 John Wiley & Sons, Ltd.     

A review of statistical methods for the evaluation of aquatic habitat suitability for instream flow assessment

Habitat models serve three main purposes: First, to predict species occurrences on the basis of abiotic and biotic variables, second to improve the understanding of species‐habitat relationships and third, to quantify habitat requirements. The use of statistical models to predict the likely occurrence or distribution of species based on relevant variables is becoming an increasingly important tool in conservation planning and wildlife management. This article aims to provide an overview of the current status of development and application of statistical methodologies for analysing the species‐environment association, with a clear emphasis on aquatic habitat. It describes the main types of univariate and multivariate techniques available for analysis of species‐environment association, and specifically focuses on the assessment of the strengths and weaknesses of the available statistical methods to estimate habitat suitability. A second objective of this article is to propose new approaches using existing statistical methods. A wide array of habitat statistical models has been developed to analyse habitat‐species relationship. Generally, physical habitat is dependent on more than one variable (e.g. depth, velocity, substrate, cover) and several suitability indices must be combined to define a composite index. Multivariate approaches are more appropriate for the analysis of aquatic habitat as they inherently consider the interrelation and correlation structure of the environmental variables. Ordinary multiple linear regression and logistic regression are popular methods often used for modelling of species and their relationships with environment. Ridge regression and Principal component regression are particularly useful when the independent variables are highly correlated. More recent regression modelling paradigms like generalized linear models (GLMs) present advantages in dealing with non‐normal environmental variables. Generalized additive models (GAMs) and artificial neural networks are better suited for analysis of non‐linear relationships between species distribution and environmental variables. The fuzzy logic approach presents advantages in dealing with uncertainties that often exist in habitat modelling. Appropriate methods for analysis of multi‐species data are also presented. Finally, the few existing comparative studies for predictive modelling are reviewed, and advantages and disadvantages of different methods are discussed. Copyright © 2006 John Wiley & Sons, Ltd.     

Field evaluation of a two‐dimensional hydrodynamic model near boulders for habitat calculation

Two‐dimensional hydrodynamic models are now widely used in aquatic habitat studies. To test the sensitivity of calculated habitat outcomes to limitations of such a model and of typical field data, bathymetry, depth and velocity data were collected for three discharges in the vicinity of two large boulders in the South Platte River (Colorado) and used in the River2D model. Simulated depth and velocity were compared with observed values at 204 locations and the differences in habitat numbers produced by observed and simulated conditions were calculated. The bulk of the differences between simulated and observed depth and velocity values were found to lie within the likely error of measurement. However, the effect of flow simulation outliers on potential habitat outcomes must be considered when using 2D models for habitat simulation. Furthermore, the shape of the habitat suitability relation can influence the effects of simulation errors. Habitat relations with steep slopes in the velocity ranges found in similar study areas are expected to be sensitive to the magnitude of error found here. Comparison of habitat values derived from simulated and observed depth and velocity revealed a small tendency to under‐predict habitat values. Published in 2009 by John Wiley & Sons, Ltd.     

Differences in physical habitat simulation system modelling results using benthic or pelagic fish species as indicators in Peruvian Andes–Amazon rivers

Aquatic organisms with different adaptations are used as indicators in physical habitat simulation system models. Those adaptations are critical for determining the shape of the weighted usable area/width curve and for recommending values of environmental flows. The main objective of this study is to compare the use of benthic native species (Astroblepus taczanowskii and Astroblepus vanceae) versus the introduced Oncorhynchus mykiss (rainbow trout) as target indicators for PHABSIM modelling in the Andean–Amazon piedmont rivers. We used adjusted probability distribution functions with L‐moments analyses for developing curves of use and preference to evaluate the efficiency of each indicator. Two hydraulic modelling sections were established in the Ulcumayo River with 21 and 27 cross sections, respectively. Native benthic species are usually dominant but scarcely used as focus organisms for environmental flows modelling. These species are associated with fast running and shallow waters, which makes them potentially more sensitive to the effects of flow reduction. Our results indicated that the native species were more restricted to velocity and depth than O. mykiss. Using selection curves in PHABSIM modelling, it is required between 10% to 94% of the mean monthly flow to preserve 90% of the available habitat for Astroblepus during the dry season (May to November). In contrast, rainbow trout requires 5% to 88% of the mean monthly flow. We conclude that a multispecies approach is useful for determining the required environmental instream flows contributing to a better sustainable condition for the Neotropical mountain rivers.     

Two‐dimensional modelling of habitat suitability as a function of discharge on two Colorado rivers

The quantity of water that should be retained in streams and rivers for the benefit of fish during periods of water scarcity is a question of considerable interest to river managers and biologists. Although instream flow methodologies have existed since the 1970s, no single method has been widely accepted for use on large warm‐water rivers because of their high species richness and generalized fish habitat use patterns. In this paper, we present an approach similar to instream flow incremental methodology, but which uses two‐dimensional flow models and biomass estimates derived from multiple sites on two Colorado rivers for predicting the effect of discharge on adult standing stocks of two native fish species. Suitability criteria are developed for bluehead and flannelmouth sucker (Catostomus discobolus and C. latipinnis) by comparing adult biomass in individual meso‐habitat units with modelled depths and velocities. We find that roundtail chub (Gila robusta) biomass is not correlated with depth and velocity, but appears to be positively associated with indices of habitat heterogeneity. Species biomass and total usable habitat area are predicted as a function of discharge for each site and data show good correlation between predicted and measured biomass. Results suggest that the Colorado and Yampa Rivers have similar potential for native fish biomass, but low summer discharges limit native fish biomass on the Yampa River. Copyright © 2005 John Wiley & Sons, Ltd.     

Stakeholder‐enhanced environmental flow assessment: The Rufiji Basin case study in Tanzania

Environmental flows are now a standard part of sustainable water management globally but are only rarely implemented. One reason may be insufficient engagement of stakeholders and their priority outcomes in the environmental flow‐setting process. A recent environmental flow assessment (EFA) in the Kilombero basin of the Rufiji River in Tanzania concentrated on a broad‐based investigation of stakeholders' use and perceptions of the ecosystem services provided by the river as a framework for the assessment of flow regimes that would maintain them. The EFA process generally followed the Building Block Methodology but within an enhanced stakeholder engagement framework. Engagement began with the involvement of institutional stakeholders to explain the purpose of the EFA and to elicit their priority outcomes. Extensive interactions with direct‐use stakeholders followed to investigate their uses of and priorities for the rivers. Results were used by the EFA specialist team in choosing flow indicators and defining measurable environmental objectives. The specialists then met to reach a consensus of the flow requirements. The EFA results were lastly reported back to stakeholders. During the Kilombero EFA, we learned that stakeholders at all levels have a good awareness of the natural services provided by a healthy river and can contribute to the setting of environmental objectives for the rivers and floodplain. These can be factored into the biophysical assessments of river flows required to maintain habitats, processes, water quality, and biodiversity. It is therefore important to allocate significant resources to stakeholder engagement. It now remains to be seen if enhanced stakeholder engagement, including the increased understanding and capacity built among all stakeholders, will increase support for the implementation of the recommended flows.     

History and review of the habitat suitability criteria curve in applied aquatic ecology

Hydraulic microhabitat assessment is a category of environmental flow tools (e.g., Physical Habitat Simulation system and other methodologically similar software) that, at its core, uses habitat suitability criteria (HSC) to link values of point hydraulic variables (usually depth, velocity, and substrate/cover) to habitat values for target life stages. Although this assessment tool has been used worldwide for decades, the history of the HSC curve is relatively unknown because the foundational information is predominantly contained in obscure and often unpublished reports. We review the history of the HSC concept in applied aquatic ecology to clarify its scientific pedigree, ensure its proper use, and build a foundation for future research. We begin the review with the formative decades of the 1950's through the 1970's, when consumptive‐based western USA water law conflicted with conservation traditions and natural resource management objectives, although water allocation issues date back at least to the 19th century. By analysing the history of the HSC concept, we aim to establish the biological, hydrologic, and geomorphological conditions that must be met for the HSC concept to be successfully employed. In spite of its documented assumptions and limitations, the HSC concept will likely continue to be a useful tool to help address water resources allocation issues in defined hydrologic and geomorphic settings. We conclude that HSC‐based methodologies should be considered as one of several environmental flow approaches involved in sustainable water resources management.     

Hydrostatic versus nonhydrostatic hydrodynamic modelling of secondary flow in a tortuously meandering river: Application of Delft3D

Given the importance of pressure gradients in driving secondary flow, it is worth studying how the modelled flow structures in a natural river bend can be impacted by the assumption of hydrodynamic pressure. In this paper, the performance of hydrostatic versus nonhydrostatic pressure assumption in the three‐dimensional (3D) hydrodynamic modelling of a tortuously meandering river is studied. Both hydrostatic and nonhydrostatic numerical models were developed using Delft3D‐Flow to predict the 3D flow field in a reach of Stillwater Creek in Ottawa, Canada. An acoustic Doppler velocimeter was employed to measure the 3D flow field at a section in a sharp bend of the simulated river at two flow stages. The results of the Delft3D hydrostatic model agreed well with the acoustic Doppler velocimeter measurements: The hydrostatic model predicted reasonably accurately both the streamwise velocity distribution across the section and the magnitude and location of the primary secondary flow cell. The results of the Delft3D nonhydrostatic approximation showed that the model was not conservative and could not accurately generate either the secondary flow or the streamwise velocity distribution. This study illustrated the superior performance of the hydrostatic over nonhydrostatic 3D modelling of the secondary flow using Delft3D. Several possible reasons for unfavourable performance of the nonhydrostatic version of Delft3D are discussed, including the pressure correction technique employed in Delft3D. Considering the uncertainties that may arise in both modelling and field measurements, the 3D hydrostatic Delft3D model was capable of reasonably predicting the river bend flow structures in the studied meandering creek.     

二维水力模拟在河流生态需水湿周法中的应用

湿周法是河流生态需水量计算中使用较为常见的一种水力学方法,通常采用一维的水力分析结果作为计算依据。二维水力模拟能提供更为细致全面的河道水力参数分布,通过对某水电站坝下13.3 km河道进行平面二维水力模拟,对其在湿周法中的应用进行了探讨。采用弗汝德数(Fr)作为浅滩生境划分标准,把浅滩生境较为集中的河段作为湿周法分析的浅滩河段。随后根据平面二维水力模拟结果,给出了浅滩断面相对湿周-流量关系曲线,采用斜率为1的斜率法计算得到了各浅滩断面的生态需水量。结果表明,采用二维水力模拟结果给出的曲线更为合理。     

Effects of habitat restoration on the macroinvertebrate fauna in a foreland along the river waal,the main distributary in the Rhine delta

River engineering in the Rhine delta and water pollution have been major threats for the ecological functioning of the river in The Netherlands. To mitigate effects of river engineering, secondary channel construction in the forelands along the existing distributaries is considered to be an important measure for river restoration. These areas are the remnants of the former Rhine floodplain and the only area where habitat restoration is possible due to the river functions assigned. Secondary channel construction in the area called ‘Gamerensche Waarden’ was taken as an example to show effects of habitat restoration on the macroinvertebrate fauna. Totally 322 macroinvertebrate taxa were found during the monitoring period. During the first 3 years species richness in the area increased rapidly due to colonization processes in the channels following habitat development. After that period total number of taxa found in the channels stabilized at around 170. A clear positive relationship was demonstrated between habitat quality and species richness. Furthermore, the density of exotic species in the secondary channels was less than in the groyne fields of the main channel. The relatively low number of taxa in polluted habitats could be explained by the presence of the PCB 28 congener. Copyright © 2007 John Wiley & Sons, Ltd.     

基于鱼类栖息地需求的雅鲁藏布江中游环境流量计算

针对水利工程影响下,河道下游天然水文情势改变造成鱼类产卵场面积减小和质量降低等潜在生态问题,通过数值模拟与统计建立拉萨裸裂尻鱼产卵期栖息地适宜度模型,采用栖息地模拟法计算了雅鲁藏布江中游藏木水电站坝下米林—尼洋河汇口处38.9 km河段的环境流量。结果表明:拉萨裸裂尻鱼产卵期适宜水深为0.7～1.0 m,适宜流速为0.4～0.6 m/s;研究河段内拉萨裸裂尻鱼产卵期环境流量为432 m~3/s。     

Distribution,movements and habitat use of channel catfish in a river with multiple low‐head dams

Channel catfish Ictalurus punctatus is a highly mobile species and is known to make extensive seasonal movements in lotic systems. Dams have been suggested to detrimentally affect this species, although abundant channel catfish populations are known to occur in many fragmented rivers. To examine factors that allow channel catfish to persist in impounded rivers, we assessed relative abundance of channel catfish in three impounded and three flowing sites of the Fox River, Illinois, USA. Radiotelemetry was used to determine movement and habitat use patterns of channel catfish among flowing and impounded areas. Relative abundance of channel catfish was consistently higher at flowing sites than at impounded sites during summer. Several radio‐tagged channel catfish moved downstream into impounded areas in fall, and all tagged individuals were found in impounded areas during winter. The majority of tagged channel catfish moved upstream into flowing areas during spring. Channel catfish used a wide range of depths (0.28–2.60 m), and were always found in current velocities less than 0.50 m s^?1. They selected most strongly for coarse substrates, but were infrequently found near cover. Although low‐head dams restrict the movements of channel catfish, impounded areas appear to provide overwintering habitats that may eliminate the need for seasonal long‐distance movements. Small run‐of‐river impoundments, however, may contain unsuitable conditions for channel catfish during other seasons. Copyright © 2010 John Wiley & Sons, Ltd.     

基于黄河鲤栖息地水文-生态响应关系的黄河下游生态流量研究

本研究采用野外生物监测、栖息地同步观测和实验室控制实验等技术手段,应用生物学、鱼类生态学、生态水力学、水文学等多学科理论,基于河流栖息地模拟法,研究了黄河下游指示物种黄河鲤生态学特性及其栖息生境与流速、水深、水温等水文水环境因子之间的关系,将径流条件与目标物种不同生长阶段生物学信息相结合,建立了代表物种繁殖期、越冬期栖息地适宜度指数,构建了黄河下游重点河段河流栖息地模型,建立了指示物种栖息地状况与河川径流条件定量响应关系,提出黄河下游花园口和利津断面繁殖期最小生态流量为300 m³/s和100 m³/s、适宜生态流量为600～700 m³/s和190～250 m³/s。该研究在水生生物习性及其与河川径流响应关系方面实现突破,解决了黄河生态需水研究中关键技术问题。     

Seasonal selection of habitat by Spotted Bass and Shorthead Redhorse in a regulated river in the Midwest,USA

Riverine fish populations depend on habitats supporting their resource and life history needs. Dynamic streamflow caused by river regulation or natural events influences the distribution of downstream habitat characteristics. Through studying habitat selection, we can identify the most utilized and valuable habitats for the success of native fishes. We determined seasonal habitat selection of two common, native fish species on the Osage River downstream of Bagnell Dam, a hydroelectric dam in central Missouri, from April 2016 to June 2017 using radio telemetry. Spotted Bass (Micropterus punctulatus) are nest‐guarders, sight feeders, and habitat generalists, whereas Shorthead Redhorse (Moxostoma macrolepidotum) are fluvial dependent, migratory, and benthic feeders. Bayesian discrete choice analyses determined that both species selected particular water depth, velocity, and presence of submerged cover in some or all seasons, even as available habitat changed. Spotted Bass selected water depths <4.0 m near submerged cover during all seasons, low velocity during spring and summer, and near‐bank habitat in all seasons except spring. Shorthead Redhorse used fast flowing habitat during spring, 0.4–1.1 m/s velocity during summer, and low velocity in fall and winter (0.1–0.5 m/s). Shorthead Redhorse used submerged cover in all seasons except summer and selected specific ranges of depth within spring (2.4–4.4 m), summer (3.3–6.7 m), and winter (1.1–2.3 m). Our findings suggest that maintaining habitats with cover and diverse water depths and velocities, particularly both low and high velocity habitats during spring, may promote resilience by providing beneficial habitats for native fishes.     

Prioritizing reaches for restoration in a regulated Alpine river: Locally driven versus hydro‐morphologically based actions

We discuss the prioritization of river reaches to be selected for restoration measures under the constraints of financial resource limitation. We propose and apply a simple approach based on the quantification of major hydro‐morphological alterations and the critical comparison with locally proposed restoration actions. The available hydro‐morphological and ecological data for the approach do not go beyond the requirements posed by the implementation of the EU Water Framework and Floods Directives. We describe an example that refers to a heavily regulated Alpine river (Sarca River, NE Italy). The results indicate hydropower facilities as a key source of hydrological alteration, with sediment retention and grade control structures on lateral tributaries playing an additional relevant role in reducing sediment supply. The frequency and duration of sediment‐transporting floods have dramatically decreased, and the bed sediment composition has been markedly altered and become highly compacted. Habitat improvement has been achieved after the implementation of minimum environmental flows. The comparison between the results of the hydro‐morphological indicators and the locally proposed restoration actions highlights that reaches with lower degree of hydro‐morphological alterations do not coincide with the areas chosen for the locally planned actions, which often miss considerations of the relevant spatial scales. In a context of limited available financial resources and data compared to other flagship river restoration projects in the European Alps, the present work suggests viable options for the choice of target restoration reaches.     

Assessing the occurrence of egg stranding for trout and salmon in a regulated river

A key challenge in many regulated rivers is to define adequate flow levels to protect aquatic organisms. Provisioning of suitable flow can be pivotal bottlenecks for fishes such as salmon and trout that use the riverbed as an incubation habitat. Additionally, the locations where females spawn will define the probability that embryos will be dewatered during the incubation period in a regulated flow regime. We investigated the water flow, dewatering, and incubation mortality in Atlantic salmon and brown trout in natural nests over 19 years in the regulated Bjoreio River in western Norway. During the study period, different flow strategies were applied to mitigate the dewatering of incubating salmon and trout embryos. Average survival in nests sampled in late winter ranged from 54% to 92% among years and was significantly correlated with the minimum water flow occurring during the incubation period. Mortality was significantly higher in nests in shallow areas, reflecting nests exposed to dewatering. The results demonstrate a strong link between incubation mortality and managed flow regimes for river spawning salmonids. Using detailed information on the nest location and incubation mortality, we estimate minimum flow requirements for this river and demonstrate an approach to effectively mitigate the impact of river regulations on embryo survival in Atlantic salmon and brown trout.     

Examining the ecological consequences of restoring flow intermittency to artificially perennial lowland streams: Patterns and predictions from the Broken—Boosey creek system in northern Victoria,Australia

The reinstatement of natural flow regimes is a rapidly emerging issue in river restoration worldwide. In northern Victoria, Australia, efforts are presently underway to restore a natural, intermittent flow regime to several streams which have received perennial diversions for both irrigation and stock and domestic water‐supplies for over 100 years. A pipeline to deliver water to landholders will significantly reduce transmission losses throughout the system allowing irrigation canals and diversion weirs to be decommissioned. The motivation for flow alteration in this system lies primarily in reducing inefficiencies in water delivery which, in turn, will be used to meet escalating demands on water resources. The ecological impact of the flow regime shift on these streams is likely to be substantial. This study utilized an existing artificial hydrological gradient (from perennial to intermittent) in two creek systems, to explore relationships between flow regime and a range of ecological variables. These data provide a benchmark against which to assess ecological changes once flow has been altered and form the basis for predicting changes that can assist future management decisions. Data collected from 10 sites across a strong hydrological gradient detected clear differences in geomorphology, water quality and biotic assemblages (macrophytes, macroinvertebrates and fish). By examining the relationship between flow regime and the distribution of biota we identify both the positive and negative outcomes of restoring naturally intermittent flow regimes within artificially perennial lowland streams. The reinstatement of intermittent flow regimes in artificially perennial streams will continue in many parts of the world as water delivery via these systems becomes increasingly uneconomical. While flow restoration may in principle be regarded as a positive step, these findings emphasize the need to consider fully the ecological consequences of restoring historical hydrological regimes to streams within the context of other human induced catchment disturbances. Copyright © 2009 John Wiley & Sons, Ltd.     

Channel recovery in a regulated river: Effects of an experimental and natural flood in the Snowy River,SE Australia

Experimental floods, generated downstream of dams, are used to recover specific bio‐geomorphic functions in regulated rivers. Studies of the effects of experimental floods vary in their objective, location, and the hydrological and bio‐geomorphic variables used to quantify recovery. Measurements of geomorphic change are required to guide future release strategies. The focus of this study was to determine if a large experimental flood in the Snowy River Australia, could promote geomorphic recovery of the river channel downstream of Jindabyne Dam following 35 years of flow regulation. The objectives of the release were to deepen, widen, and increase channel capacity and coarsen the riverbed substratum in the Jindabyne Gorge and Dalgety Uplands sections of the Snowy River. Data from the release were compared with that of a natural flood event that occurred after the experimental flow event. Both events showed channel adjustments and a degree of geomorphic recovery, but this varied between the two river sections. Marked channel adjustments occurred in the Dalgety Uplands reach following both the experimental and natural flood event and in the Jindabyne Gorge section following the natural flood event. Geomorphic changes were related to the hydrological character of each flood event. The number of flood peaks, the sequence of peaks, the flood duration, and the total energy expenditure differed markedly between the two events, and these four flood hydrological characteristics explained the greater geomorphic recovery associated with the natural flood event in the Jindabyne Gorge. No clear hydro‐geomorphic relationship was derived for channel change in the Dalgety Uplands where existing morphological constraints limit flood effectiveness.     

A two‐dimensional self‐adaptive hydrodynamic scheme for the assessment of the effects of structures on flooding phenomena in river basins

In order to assess the effects of river and floodplain engineering projects on flooding, a new self‐adaptive hydrodynamic scheme for the simulation of two‐dimensional river flows is proposed. The depth‐averaged motion equations are solved numerically using a fractional step method, in which the convective terms are calculated using the inverse characteristics method and the remaining terms with an explicit method based on a finite difference method. The integration is performed on a dynamically self‐adaptive calculus grid, which allows representation of the movable boundary between wetting and drying regions of the basins to follow the effective development, in time and space, of the expansion phenomenon of flood. The proposed procedure allows the grid's dynamic refinement to avoid coordinate transformation or the use of unstructured grids. The proposed method is simple and allows the thickening of the grid to accommodate the flooding phenomena on the floodplain and to calculate the velocity in the domain regions in which a higher space resolution is required. Therefore, flows running through structures such as weirs, gates, bridges or culverts can be simulated. In the paper two different case studies, approached with the proposed self‐adaptive calculation scheme, are discussed. The studies concern the analysis of the effects of structures, such as roads or embankments, on flooding phenomena in the Tiber and Tanaro basins respectively. Copyright © 2003 John Wiley & Sons, Ltd.