Small Hydraulic Structures Research Articles

Hyper-resolution flood hazard mapping at the national scale

Abstract. Flood hazard mapping is currently in a transitional phase involving the use of data and methods that were traditionally in the domain of local studies in a regional or nationwide context. Challenges include the representation of local information such as hydrological particularities and small hydraulic structures, as well as computational and labour costs. This paper proposes a methodology of flood hazard mapping that merges the best of the two worlds (local and regional studies) based on experiences in Austria. The analysis steps include (a) quality control and correction of river network and catchment boundary data; (b) estimation of flood discharge peaks and volumes on the entire river network; (c) creation of a digital elevation model (DEM) that is consistent with all relevant flood information, including riverbed geometry; and (d) simulation of inundation patterns and velocities associated with a consistent flood return period across the entire river network. In each step, automatic methods are combined with manual interventions in order to maximise the efficiency and at the same time ensure estimation accuracy similar to that of local studies. The accuracy of the estimates is evaluated in each step. The study uses flood discharge records from 781 stations to estimate flood hazard patterns of a given return period at a resolution of 2 m over a total stream length of 38 000 km. It is argued that a combined local–regional methodology will advance flood mapping, making it even more useful in nationwide or global contexts.

Maximum energy loss in a vertical drop equipped with horizontal screen with downstream rough and smooth bed

Abstract Screens are one of the recent energy dissipator structures that can be used downstream of small hydraulic structures. In this study, screens were used horizontally at the brinks of the vertical drop with downstream smooth and rough bed to investigate the energy loss of the drop. Experiments were performed on two porosities of screens, a relative critical depth of 0.13–0.39 and a median size of 1.9 cm aggregates. The results showed that for a relative critical depth of more than 0.3 in a vertical drop equipped with a screen with a rough bed, the drop length with respect to smooth bed increases. Compared to applying a Type I stilling basin, a vertical drop equipped with a screen with downstream smooth and rough bed reduces the drop length by approximately 50%. Although a rough bed increases air entrainment, it has no effect on the energy loss and pool depth of a vertical drop equipped with a horizontal screen with smooth bed. The use of horizontal screens at the brinks of the vertical drop causes maximum energy loss in the downstream of drop. Equations were provided to estimate the flow parameters with a R2 value of more than 0.925 and a normalized root mean square error of less than 0.04.

Energy dissipation in hydraulic jumps using triple screen layers

In the present study, series of laboratory experiments were conducted to investigate the effectiveness of perforated screens as energy dissipators in mixed triple wall mode in the case of small hydraulic structures. The shapes of openings for each layer of screens were either circular, square or triangular. Every layer of the screen had a porosity of 45% per unit depth of the screen. The experiments were conducted to dissipate the energy for supercritical flows of Froude number F1 ranging from 3.2 to 19.3. The screens were placed vertically with the first screen 1.5 m from the sluice gate and consecutive screen at a gap of 25 mm. The experiments showed that the energy of the supercritical flows can be dissipated effectively by using perforated screens. The difference in energy dissipation between the upstream and downstream of the screen was more significant than the energy dissipation caused by classical hydraulic jumps. Comparing the results of the present study with the previous researchers it is found that the energy loss in case of present study more than the previous researchers. The relative energy loss in the present study was found to be varying from 74 to 94%. The value of the Froude number downstream of the screen, F2, was varying from 1.1 to 1.81, with an average value of 1.35. Tailwater deficit parameter, D, if found to be varying from 0.66 to 0.90.

Monitoring of the Technical Condition and Optimisation of the Functioning of Small Hydraulic Structures in Poland: The Case Study of the Oświecim Weir

Successively conducted monitoring and inspections allow for the detection of emerging issues and their elimination. The objective of this study is the analysis of the administrative procedures related to the monitoring of the technical condition of small hydraulic structures in Poland. The case study of the Oświecim Weir on the Prosna River presents the parameters subject to assessment and further activities aimed at the elimination of the detected defects. The obtained results showed damage to its concrete structures, including cracks and cavities. The undertaken activities related to the complete remodelling of the Oświecim Weir and the incurred costs generally result from the environmental conditions (water flows in the Prosna River), directly causing the necessity for the stabilisation of water conditions in the area. In the context of the observed climatic changes, the problem is faced by more and more regions around the globe. The proper technical condition of hydraulic structures, resulting from diligent monitoring, provides the basis for the mitigation of this unfavourable situation.

Implication of partial duration series on regional flood frequency analysis

ABSTRACT In the regional flood frequency analysis, the selection of important site characteristics and a suitable number of clusters have a significant role in finding homogeneous regions. Generally, it is difficult to determine the exceedance threshold value or the number of average peaks per year (λ) in Partial Duration Series (PDS), and this difficulty is intensified in the context of regional frequency analysis, though, there are only limited studies to report this difficulty. In the present study, the Mahanadi basin is divided into homogeneous regions by using fifteen effective variables by applying different clustering techniques. Factor analysis has been introduced in finding suitable site variables. Out of fifteen variables, nine variables are selected based on factor analysis loadings. Two hard clustering techniques i.e. Hierarchical (HC), K-Means Clustering (KM) along with the Fuzzy C-Mean Clustering (FCM) techniques are used for finding out the possible number of clusters. To validate the results we used cluster validation indices to locate the optimal number of clusters. Results of the homogeneous region found from the FCM and KM hard clustering approach are more accurate and more robust than HC. The suitability of many frequency distributions to be used in the regional frequency is inspected. The results confirmed that the Generalized Pareto (GP) best described the PDS in the study area and also, show that the best PDS/GP performance is found in almost all the values of λ (2, 2.5, and 3). To test the homogeneity and to identify the best-fit frequency distribution, a regional L-moment algorithm is used. A unique regional flood frequency equation is developed which estimates the flood quantiles of ungauged catchments for each region of the basin and an index flood is also specified concerning catchment characteristics by using the multiple linear regression approach for designing small and medium hydraulic structures in the basin. The results are compared with the previous studies of flood frequency in this basin.

Application of Multi-Criteria Analytic Methods in the Assessment of the Technical Conditions of Small Hydraulic Structures

Increasing water demand, combined with unfavourable climate change, creates a need for well-thought-out water management. Such goals are realised thanks to appropriate hydrotechnical infrastructure, the efficiency and functionality of which depend on its technical condition. In the literature, there is no method for the assessment of the technical condition of small damming structures, including sluice gates. The aim of this article was to present the possibility of using the multi-criteria AHP decision support method to assess the technical condition of small damming structures. The assessment included both concrete elements (spillways, abutments, and apron) and steel elements (gates and hoisting equipment). The analyses considered the effects of growing vegetation, the condition of concrete surfaces (e.g., cracks, cavities, exposed rebar) and steel elements (corrosion, deterioration). A hybrid method was used to study the assessment of the technical condition of water structures. It consisted of a modified Zawadzki’s method and weights which were determined by different groups of respondents with industry backgrounds (university students and experts) using the AHP method. The obtained results show that the factors related to the holes and corrosion of the gate elements had the highest value of the matrix solution vector. The last level of the tree structure indicated that the condition of the spillway and gate is the most important factor in the technical condition assessment. As the assessment considers commonly available parameters, the proposed method is universal and can be used in the assessment of other structures of this type in different regions of the world, which is important in terms of their functioning, planned repairs, and optimal use in water resource management.

Small hydraulic structures, big environmental problems: is it possible to mitigate the negative impacts of culverts on stream biota?

This study is a broad and critical review of the transdisciplinary literature on the construction of culverts and their impacts on stream hydrology and geomorphology as well as on stream habitats and biota. For engineers, a culvert is a structure, usually of the tunnel type, that transfers a stream or open drain under a road, railway line, or other obstacle from one side to the other. In fact, culverts are complex hydraulic structures whose impacts on stream ecosystems must be evaluated and understood before they are designed. The objective of this paper is to analyse and discuss recent knowledge about culvert functioning in terms of their negative effects on the passage of freshwater biota, particularly fish, and on entire stream ecosystems. We present the results of many studies showing that improperly designed culverts are barriers for migrating animals and usually have serious ecological consequences (mainly disturbances to fish life history). We also pay attention to different culvert modification methods that increase their passability for organisms and mitigate the impacts of culverts on the surrounding environment. The other purpose of this review is therefore to emphasize that the integration of the knowledge and professional experience of biologists and ecologists with those of river managers, river engineers, hydraulic engineers, hydrologists, and geomorphologists is necessary to design culverts that preserve the natural properties of streams.

Generation of IDF Equation from Catchment Delineation Using GIS

The study was intended to find out the catchment characteristics of an area and the IDF (Intensity-Duration-Frequency) analysis of rainfall of that area using Gumbel method and Log Pearson type III method. In different studies, the IDF equations are generated for an area without acknowledging the catchment, stream length of the catchment and the time of concentration. In our study the Digital Elevation Map (DEM) of Dhaka was used. The DEM was analyzed using QGIS to find out different catchments, catchment area, catchment slope, stream length etc. The rainfall data of 18 years was collected from BMD (Bangladesh Meteorological Department) at 24 hours’ interval. This rainfall data was analyzed using Gumbel method and Log Pearson Type III method because these methods give accurate prediction for return period more than the range of the acquired data. The return period was taken as 2 years,5 years,10 years,25 years,50 years and 100 years. Finally, the intensity for different return period was plotted against the duration of the rainfall to find out the IDF curve. For any kind of rainfall analysis to find the peak discharge for designing storm sewage lines, small hydraulic structures or calculating surface runoff, infiltration, sub-surface runoff, discharge at rivers or water bodies, the derived IDF equations can be used. Even to find out peak discharge with a return period more than 18 years these set of equation can be used. This method can also be used in other sub urban or urban areas to find out the time of concentration of that catchment and IDF relationships for short duration rainfalls.

Effect of using grouted vertical barrier on seepage characteristics under small hydraulic structures

This study investigated the effect of using Grouted Vertical Barrier (GVB) on the seepage characteristics (uplift force, seepage rate, and exit hydraulic gradient) under small hydraulic structures. The GVB’s variables, viz., position, depth, width and hydraulic conductivity, were studied experimentally using sand model and numerically employing SEEP/W software. A parametric study investigated several cases of the variables after numerical model verification. The results depicted that the heal and toe ends were the best positions for uplift force and exit gradient, respectively. The maximum reduction in the seepage occurred at both ends. The seepage characteristics swiftly decreased by increasing the GVB’s depth in the pre-mentioned best positions. Upsurge of the GVB’s width sequentially reduced the exit gradient and the seepage rate, whilst negatively impacted the uplift force. Declining the ratio between the hydraulic conductivity of the GVB (K) and the reference soil one (Ko) significantly lowered the seepage until reaching a stationary proportion K/Ko = 1E−4. Beyond this, decreasing K/Ko ratio do-nothing. Through regression analysis, three equations were developed to estimate the seepage characteristics affected by GVB’s variables. The indications of comparative studies revealed a better effect of the GVB compared to any of the sheet pile or the upstream blanket.

Sensitivity of Australian roof drainage structures to design rainfall variability and climatic change

The main design determinant for small catchment hydraulic structures is rainfall intensity. Localised relationships between rainfall intensity, frequency and duration (IFD) are used to design each structure to a specified level of performance. However, limitations in rainfall observations introduce uncertainty in IFD values. Further, this uncertainty is compounded by changes in climatic conditions via anthropogenic forcing. Whether this is a cause for concern depends on the structure's sensitivity to deviations away from design rainfall values. Here, we investigate the ability of roof drainage systems to accommodate deviations in design rainfall. We assess the sensitivity of box gutter overflow designs across Australia to spatial variability in IFD values, and projections of IFD values due to climatic change. Different overflow designs were found to have markedly variable responses to rainfall intensity increases, from 13% to 406% before failure. Potential increases in rainfall intensity from spatial variability uncertainty varied from 2 to 54%. While rainfall projections for the 2090 decade ranged from −15 to +59%. Rainfall intensity increases as high as 259% were noted when both sources of uncertainty were combined for a temperature rise scenario of 5 °C. At the majority of locations coupled increases in rainfall intensity were primarily driven by existing rather than future uncertainties for a 2 °C temperature rise scenario. Considering design rainfall uncertainties in terms of design sensitivity shows that adapting to present and future uncertainties can come at no additional cost for some design options while other options need to be altered to reduce the risk of failure.

Changes in flood characteristics and the flood driving mechanism in the mountainous Haihe River Basin, China

ABSTRACTRecently, the land surface in the Haihe River basin has changed, influencing the flood processes in the basin. To quantify this impact, seven typical sub-catchments were selected from different hydrological regions of the Haihe River basin for study. The non-parametric Mann-Kendall test was used to analyse for trends, and the non-parametric Pettitt test was adopted to detect any change point in the flood time series. Then, a hydrological model was established to simulate the effects of each potential driving factor on flood peak and volume. It was shown that flood peak and volume time series had decreased significantly, and the change point was around the year 1980. Groundwater depletion was not the main contribution to flood peak (FP) and volume (FV) decrease. In the Shifokou, Mubi and Lengkou sub-catchments, small hydraulic structures are the main driving factors for FP and FV decreasing. In the Xitaiyu, Daomaguan and Fuping sub-catchments, both land-use change and hydraulic structures are the main driving factors. The decreasing percentage decreases with the increase of the flood magnitude. The results provide valuable information for flood simulation and control in the Haihe River basin.

A new method to estimate the total drainage area of soil-water conservation projects on the upstream of Wangkuai watershed in Daqinghe River basin, China

Abstract A new approach was presented to calculate the total drainage area (TDA) of many small hydraulic engineering projects on the upstream Wangkuai reservoir watershed considering flood scaling. By establishing the correlation of flood peak between Wangkuai and Fuping hydrological station, the event-based flood scaling in Wangkuai reservoir watershed was analyzed and the scaling exponent θ was 0.5688. Relations between flood peak and maximum 3 h rainfall amount were fitted for the undisturbed and disturbed periods to analyze the effect of small reservoirs on the flood peak. The average change ratio of flood peak was 15.05% and the TDA of small hydraulic structures was 939.88 km2.

Calculation of nonstationary flood return period considering historical extraordinary flood events

With climate change and intensification of human activities, the flood generation mechanism has been influenced which results in the nonstationarity of flood time series. In this study, in order to use historical flood data for flood frequency analysis, a nonlinear AutoRegressive exogenous (ARX) model was employed to complement missing flood data between the historical and recorded data. The key statistics of the complemented time series agreed well with those of the documented record. Using EWT (the expected waiting time until an exceedance) and ENE (the expected number of events in m year is one), nonstationary flood return periods were estimated by the complemented and recorded annual maximum flood peak series, respectively. The results showed that the return levels under nonstationarity are smaller than those under stationarity due to the construction of small hydraulic structures and many check dams after 1980s. This study implies that it is necessary to refine the flood return levels and the corresponding flood control measures for nonstationary flood series due to environmental change.

Investigating Effect of Different Parameters of the Submerged Vanes on the Lateral Intake Discharge Located in the 180 Degree Bend Using the Numerical Model

Intakes are widely used for flow diversion and its control in the open channels or rivers. During passing flow, part of the suspended sediment along with the flow enters the lateral channel and deposits in the lateral intake channel entrance, causing a change in the direction of the flow line towards the shore in front of the reservoir, which reduces the intake efficiency. Submerged vanes are small hydraulic structures that, by creating a secondary flow in their downstream, cause changes in the flow pattern and guide line to the drainage span, and the most important parameters affecting sediment input to the waterfall is the ratio of flow rate. Investigating a laboratory model has high costs and times, which in some cases cannot be justified, therefore, suitable numerical models can be proposed for such options. In this study, using Flow3D, three-dimensional numerical modeling of the flow was calibrated and verified using existing data and numerical modeling accuracy, the relative error of the numerical model was determined. In this study, all effective parameters including submerged vanes type, submerged vanes number, submerged vanes size and Froude number changes in the main channel and type of submerged vanes layout have been investigated. The results of the numerical model show that the angle of inclination of 60 degrees in the entrance intake and the chassis layout in the Froude numbers 0.21-0.33 will result in the most lateral intake discharge.

Optimum Dimensions of Hydraulic Structures and Foundation Using Genetic Algorithm coupled with Artificial Neural Network

A model using the artificial neural networks and genetic algorithm technique is developed for obtaining optimum dimensions of the foundation length and protections of small hydraulic structures. The procedure involves optimizing an objective function comprising a weighted summation of the state variables. The decision variables considered in the optimization are the upstream and downstream cutoffs lengths and their angles of inclination, the foundation length, and the length of the downstream soil protection. These were obtained for a given maximum difference in head, depth of impervious layer and degree of anisotropy. The optimization carried out is subjected to constraints that ensure a safe structure against the uplift pressure force and sufficient protection length at the downstream side of the structure to overcome an excessive exit gradient. The Geo-studio software was used to analyze 1200 different cases. For each case thelength of protection (L) and volume of structure (V) required to satisfy the safety factors mentioned previously were estimated for the input values, namely, the upstream cutoff depth (S1), the downstream cutoff depth (S2), the foundation width (B), the angle of inclination of the upstream cutoff (Ɵ1) and the angle of inclination of the downstream cutoff (Ɵ2), H (differencehead), kr (degree of anisotropy) and D (depth of impervious layer). An ANN model was developed and verified using these cases input-output sets as its data base. A MatLAB code was written to perform a genetic algorithm optimization modeling coupled with this ANN model using a formulated optimization model. A sensitivity analysis was done for selecting the crossover probability, the mutation probability and level,the number of population, the position of the crossover and the weights distribution for all the terms of the objective function. Results indicate that the most factors that affects. the optimum solution is the $ number of population required. The minimum value that gives stable global optimum solution of this parameter is (30000) while other variables have little effect on the optimum solution.

Nonstationary Flood Frequency Analysis for Annual Flood Peak Series, Adopting Climate Indices and Check Dam Index as Covariates

Traditionally, flood frequency analysis under the assumption of stationarity has been a cornerstone and there is mature technology applied in practice. However, recent evidences of the impact of climate variability and anthropogenic factors have thrown into question the applicability of stationary hypothesis. In this study, Kendall’s tau and Spearman’s rho correlation test were adopted to detect the relationship between climate indices (PDO, NAO, AO, NPO and ENSO) and annual flood peak data. The test results showed that NPO and Nino3 had significant correlations with the flood peak which could prove the climate cause of non-stationarity. Nino3 is used herein to describe ENSO. We also proposed a check dam index (CDIp) to represent the effect of human activities that caused nonstationarity on flood. The CDIp was based on the estimated storage capacity and drainage area of large number of check dams and small hydraulic structures. A framework for nonstationary flood frequency analysis was developed through Generalized Additive Models in Location, Scale and Shape (GAMLSS), and two models based on GAMLSS were applied to the annual flood peak. The model results that incorporated climate indices (NPO and Nino3) and CDIp as covariates in the parameters of the selected distribution exhibited an undulate behavior, which could better describe nonstationarity than the model with only time dependence. For a reservoir index (RI) proposed by Lopez and Frances (2013) which is similar to CDIp, we established two contrast models and the result revealed that CDIp is superior to RI. These results highlight the necessity of flood frequency analysis under nonstationary conditions, and alternative definitions of return period should be adapted.

Challenges of Traditional Rainwater Harvesting Systems in Tunisia

The main objective of this article is to examine the relevance of traditional hydraulic systems in ensuring sustainable water supplies at the catchment level and to explore ways to involve farmers in rural development. The methodology we used is based on the analysis of the Tunisian experience with traditional hydraulic systems to conserve water and soil. We proceed with a description of new forms of small hydraulic structures, which, since 1960, have increased significantly throughout the arid and semiarid landscape of Tunisia. We present a strategic framework related to the mobilization of water and to the institutions operating in the field of hydro-agricultural business techniques. The findings can contribute to promoting efficient and sustainable hydro-agricultural structures among decision makers and agricultural stakeholders regarding their future projects. The conclusions we draw can also help to stimulate new thinking about current and future agricultural, social, and economic challenges not only within Tunisia but also in other arid countries in the MENA (Middle East and North Africa) region.

Water management plan for olive orchards in a semi-mountainous area of Crete, Greece

<div> <p>In the present work the physically based distributed rainfall–runoff modeling system, MIKE SHE, is used to simulate the surface runoff at a semi-mountainous impermeable area of Tavronitis River basin in Crete-Greece.  The objective of this surface flow model is to develop an appropriate irrigation plan for olive trees. For the model calibration, a simulation time of one year (01/09/2000 - 31/08/2001) was considered, while for the model verification a two-year period (01/09/2001 - 31/08/2003). During these periods river flow measurements were obtained at two specified locations. These measurements were employed as targets for calibration and verification of the surface flow model. After the successful calibration and validation processes, the 2D maps of the overland flow were produced. Using these maps, the locations of significant surface water accumulation in the study region and for a specific time period were identified. Next, these locations were proposed for the construction of potential small hydraulic structures (dam or/and reservoir), for covering the irrigation needs of olive trees in the study area. </p> </div> <p> </p>

Evaluation of Nonstationarity in Annual Maximum Flood Series and the Associations with Large-scale Climate Patterns and Human Activities

Recent evidences of the impact of regional climate variability, coupled with the intensification of human activities, have led hydrologists to study flood regime without applying the hypothesis of stationarity. In this study, identification of nonstationarity was conducted in the form of both trend and change point in the mean of the annual maximum flood magnitudes, using Mann-Kendall and Pettitt test, respectively in Wangkuai reservoir watershed, China. The annual maximum flood series exhibited a significant decreasing trend, and the timing of change point was detected in 1979, which was consistent with the construction of large numbers of check dams and small hydraulic structures. A correlation test (Pearson correlation test) between large-scale oceanic-atmospheric patterns (El Nino Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), North Pacific Oscillation (NPO), North Atlantic Oscillation (NAO), Atlantic Oscillation (AO)) and annual maximum flood peaks was adopted to assess the climatic causes of nonstationary flood series. It was found that NPO, NAO and AO had significant correlations with flood peak, but ENSO and PDO could not explain the variations of flood peak. In the case of human-induced nonstationarity, we proposed 2 new indices to represent the effect of human activities on flood. The new indices were proposed based on the storage capacity and drainage area of the large numbers of check dams and small hydraulic structures which were estimated with no observed data. The identification of nonstationarity for flood series and the climatic and human-induced causes could provide useful information in nonstationary flood frequency analysis.

Experimental investigation of screens as energy dissipaters in submerged hydraulic jump

This study investigated the effectiveness of screens as energy dissipaters in small hydraulic structures using physical experiments. In the experimental design, the Froude number, screen arrangements, and screen porosity were the major controlling parameters. The experiments covered a range of Froude numbers between 2.5 and 8.5, screen porosity of 40% and 50%, and gaps of double screens between 1 and 5 cm. The main goal of this study was investigation of the screens creating submerged hydraulic jumps. The flow depth was digitally measured in order to perceive the turbulences and validate the results of energy dissipation against those of the methods in the literature. The experimental results show the importance of each parameter on the screen performance. The screens with double arrangement with the imposed hydraulic jump dissipated more energy. The gaps of the double arrangement had an insignificant effect on energy dissipation. The double screen with porosity of 40% had the best performance. Since the Froude number was found to be the most effective parameter, quadratic equations as a function of this number were fitted to the experimental results with high R$^{2}$ and very low RMSE values. The quadratic equations can be employed as interpolators and/or extrapolators.