River Cross-section Research Articles

Inaccuracy introduced by LiDAR-generated cross sections and its impact on 1D hydrodynamic simulations

High-quality topographic data is an essential prerequisite for any hydrologic simulation. In recent years, LiDAR measurements have been used as a reliable method for obtaining such data even though it has its own flaws. This article focuses on analysis of error introduced by LiDAR-based elevation scanning due to the fact that the near-IR laser beam (1,064 nm) cannot penetrate water masses. Such error may affect derived structures (cross sections) and it influences hydrodynamic simulations as well. Motivation for our research was mainly the insufficient amount of measured cross sections on tributary channels in our study area (Moravian-Silesian Region) and evaluation/correction of error dragged into hydrodynamic modeling when LiDAR-based cross sections are used instead. In our article, we compared two data sets of cross sections: real cross sections created from direct measurements of the river channel and cross sections of the same river channel extracted from LiDAR (9 cross sections, 0.2 m LiDAR DEM resolution, gauge stations and floodplains data were used). As it was expected, the inaccuracies between these two cross-section data sets radically affected the results of the HEC-RAS simulation in the study area (the confluence of rivers Olse and Stonavka). Some known methods for depth estimation and flow area estimation were used for correction of these errors and as a conclusion of the study a recommendation is presented: inaccuracies introduces by LiDAR’s inability to penetrate water masses must be taken into account and must be corrected according to the catchment-specific conditions. We also showed that double-linear depth estimation method works well when dealing with low-flow conditions in upland catchment study area.

Simplified Flood Inundation Mapping Based On Flood Elevation-Discharge Rating Curves Using Satellite Images in Gauged Watersheds

This study suggests an approach to obtain flood extent boundaries using spatial analysis based on Landsat-5 Thematic Mapper imageries and the digital elevation model. The suggested approach firstly extracts the flood inundation areas using the ISODATA image-processing algorithm from four Landsat 5TM imageries. Then, the ground elevations at the intersections of the extracted flood extent boundaries and the specified river cross sections are read from the digital elevation to estimate the elevation-discharge relationship. Lastly, the flood extent is generated based on the estimated elevation-discharge relationship. The methodology was tested over two river reaches in Indiana, United States. The estimated elevation-discharge relationship showed a good match with the correlation coefficients varying between 0.82 and 0.99. In addition, self-validation was also performed for the estimated spatial extent of the flood by comparing it to the waterbody extracted from the Landsat images used to develop the elevation-discharge relationship. The result indicated that the match between the estimated and the extracted flood extents was better with higher flood magnitude. We expect that the suggested methodology will help under-developed and developing countries to obtain flood maps, which have difficulties getting flood maps through traditional approaches based on computer modeling.

Three Methods for Estimating the Entropy Parameter M Based on a Decreasing Number of Velocity Measurements in a River Cross-Section

The theoretical development and practical application of three new methods for estimating the entropy parameter M used within the framework of the entropy method proposed by Chiu in the 1980s as a valid alternative to the velocity-area method for measuring the discharge in a river is here illustrated. The first method is based on reproducing the cumulative velocity distribution function associated with a flood event and requires measurements regarding the entire cross-section, whereas, in the second and third method, the estimate of M is based on reproducing the cross-sectional mean velocity by following two different procedures. Both of them rely on the entropy parameter M alone and look for that value of M that brings two different estimates of , obtained by using two different M-dependent-approaches, as close as possible. From an operational viewpoint, the acquisition of velocity data becomes increasingly simplified going from the first to the third approach, which uses only one surface velocity measurement. The procedures proposed are applied in a case study based on the Ponte Nuovo hydrometric station on the Tiber River in central Italy.

PENGARUH BENDUNG TERHADAP PROFIL MUKA AIR SUNGAI BATANG GADIS

Placement of the weir in the river Batang Gadis will cause population anxiety in the village Pulungan which located upstream weir as far as 3 km, due to a weir can cause water surface profile of the river getting higher and ultimately to increase the pool of flooding in residential areas.Assuming modeling of river a uniform flow, river cross-section has a rectangular shape with width 50 m and 40 m, the roughness Manning 0.0025, the profile of water flow floods that occurred in 2 yaears, 25 years, and 100 years before and after the existing weir can be calculated by numerical integration methods. From the calculation, the length of the water behind the weir is 1.4 km upstream towards the weir, which means that the depth of the water level rises to as far as 1.4 km and after that the depth of water before and after there the weir is same. Because the village Pulungan located 3 km to the upstream, the weir did not affect the increase in the flood waters in the village Pulungan. At 2 years flood discharge does not cause inundation in the village Pulungan, but the flood discharge 25 years and 100 years has led to inundation in the village Pulungan with the depth of each pool 0.971 m and 1.675 m. Keywords: uniform flow, numerical integration, inundation, flood discharge.

Calibration and Validation of a Distributed Energy–Water Balance Model Using Satellite Data of Land Surface Temperature and Ground Discharge Measurements

Abstract Distributed hydrological models of energy and mass balance need as inputs many soil and vegetation parameters, which are usually difficult to define. This paper will try to approach this problem by performing a pixel to pixel calibration procedure of soil hydraulic and vegetation parameters based on satellite land surface temperature data as a complementary method to the traditional calibration with ground discharge measurements at river control cross sections. These analyses are performed for the upper Po River basin (Italy) closed at the river cross section of Ponte della Becca with a total catchment area of about 38 000 km2, for a calibration period from 2000 to 2003, and a validation period from 2004 to 2010. Moderate Resolution Imaging Spectroradiometer (MODIS) land surface temperature data and a distributed hydrological model, Flash-Flood Event-Based Spatially Distributed Rainfall-Runoff Transformation Energy Water Balance model (FEST-EWB), that solves the system of energy and mass balance equations as a function of the representative equilibrium temperature will be used. This equilibrium surface temperature is comparable to the land surface temperature as retrieved from operational remote sensing data. Results suggest that a combined calibration based on satellite land surface temperature and ground discharge is needed to correctly reproduce volume discharge and also spatially distributed maps of representative equilibrium temperature and evapotranspiration. Improvements of about 10 mm/8 days are obtained on evapotranspiration from the model calibrated with Q and land surface temperature (LST) respect to the calibration based only on discharge.

LIDAR DATA RESOLUTION VERSUS HYDRO-MORPHOLOGICAL MODELS FOR FLOOD RISK ASSESSMENT

Abstract. Uncertainties in topographic data have a significant influence on hydro-morphological and hydraulic predictions and therefore on flood risk assessment. In this work, the effects of topographic data resolution on the results of hydro-morphologic and hydraulic simulations are analysed using respectively the morphological bi-dimensional curvilinear model MIKE 21C and mono-bidimensional SOBEK. The studies have been carried out in the Torre river, located in Northern Italy. The evaluations on hydro-morphological and hydraulic risk require accurate spatial information for the area of interest. In order to characterize the river morphology, mainly for large areas, the availability of high resolution topography derived by airborne laser scanner represents an effective tool. Nowadays LiDAR (Light Detection And Ranging) DTM covering large areas are readily available for public authorities, and there is a greater and more widespread interest in the application of such information for the development of automated methods aimed at solving geomorphological and hydrological problems. For the models analysed, high-resolution LiDAR data were used to create the basic topographic information. An additional source for the topography of the Torre river has been provided by river cross-section data. Digital elevation models at different resolution have been created to test the effects of different grid cell sizes on the simulations. The impact of topographic information on hydraulic and morphological model results was evaluated for the area through a comparison of results. Additionally, morphologic variations and position of erosional and depositional zones along the watercourse and variations in flood extent and dynamics have been investigated. The obtained results emphasise the importance of quality of input information for reliable results of hydraulic and sediment transport models. Criteria for selecting the optimal DTM resolution are suggested, based on the quality of available data.

RIO SOLIETTE (HAITI): AN INTERNATIONAL INITIATIVE FOR FLOOD-HAZARD ASSESSMENT AND MITIGATION

Abstract. Natural catastrophic events are one of most critical aspects for health and economy all around the world. However, the impact in a poor region can impact more dramatically than in others countries. Isla Hispaniola (Haiti and the Dominican Republic), one of the poorest regions of the planet, has repeatedly been hit by catastrophic natural disasters that caused incalculable human and economic losses. After the catastrophic flood event occurred in the basin of River Soliette on May 24th, 2004, the General Direction for Development and Cooperation of the Italian Department of Foreign Affairs funded an international cooperation initiative (ICI) coordinated by the University of Bologna, that involved Haitian and Dominican institutions.Main purpose of the ICI was hydrological and hydraulic analysis of the May 2004 flood event aimed at formulating a suitable and affordable flood risk mitigation plan, consisting of structural and non-structural measures. In this contest, a topographic survey was necessary to realize the hydrological model and to improve the knowledge in some areas candidates to be site for mitigation measures.To overcome the difficulties arising from the narrowness of funds, surveyors and limited time available for the survey, only GPS technique have been used, both for framing aspects (using PPP approach), and for geometrical survey of the river by means of river cross-sections and detailed surveys in two areas (RTK technique). This allowed us to reconstruct both the river geometry and the DTM’s of two expansion areas (useful for design hydraulic solutions for mitigate flood-hazard risk).

Response of fish and benthic invertebrate communities to constrained channel conditions in a mountain river: Case study of the Biała, Polish Carpathians

Abstract Following considerable hydromorphological degradation in past decades, the gravel-bed Biala River, Polish Carpathians, is to be restored through establishing erodible corridor in two river sections. In these sections, relatively long, unmanaged channel reaches alternate with short, channelized reaches located in the vicinity of bridges. Effects of the alternating morphologies on physical habitat conditions, fish and benthic invertebrate communities, and ecological river quality were investigated in 10 pairs of unmanaged and channelized cross-sections located between significant tributaries. Unmanaged cross-sections with an average of two low-flow channels exhibited significantly greater variation in depth-averaged and near-bed velocity and bed material size than single-thread, channelized cross-sections. Summer, autumn and winter surveys of benthic invertebrates indicated that the unmanaged cross-sections typically hosted three times more taxa than channelized cross-sections, and this was reflected in distinct appraisal of the two cross-section types by means of invertebrate-based BMWP-PL index. Electrofishing indicated no statistically significant difference in the number of fish species between both types of river cross-sections, and the resultant similar scores of the European Fish Index allowed both cross-section types to be associated with the same class of ecological river quality. This study indicated that short channelized river reaches do not disrupt continuity of fish populations, although they provide worse habitats for fish, reflected in the lower numbers of individuals, especially juveniles. It also highlighted the need of investigating various groups of river biota to determine the response of river biocoenosis to environmental stressors and evaluate the ecological status of the river.

Multi-frequency acoustics for suspended sediment studies: an application in the Parana River

A method of using two acoustic Doppler current profilers operating at different frequencies and employed at the same measuring vertical to sample a profile of suspended sediment concentration has been previously applied in the Parana River (Argentina) but has not been validated by direct sediment samples. The present work fills this gap by reporting new field data and comparing them with acoustically inferred sediment concentrations. The agreement between directly measured sediment concentrations and grain sizes with corresponding estimates from an employed backscatter model was found to be good (squared correlation coefficients are 0.9 and 0.8, and mean deviations are 14 and 6%, respectively). The interrelations between flow velocity and suspended sediment concentration at fixed locations and in a moving mode along a river cross-section have been also investigated. Observed events of bed sediment re-suspension were found to be highly correlated with fluctuations of the vertical flow velocity, with a 100–150s quasi-periodicity. The size of re-suspension plumes was increasing from the channel thalweg to the low-submerged bar areas.

선진화된 하천측량자료 활용 및 관리를 위한 하상변동 자료관리 프로그램 기반의 하도유지관리체계 개선에 관한 연구

ABSTRACT The systematic management of river is difficult due to various environmental factors such as season and terrain deformation. Especially, river terrain are rapidly changing by natural and anthropogenic factors such as torrential rain during the summer and river development projects. Thus in this conditions, building the advanced river management system is an essential condition to support the ongoing management of survey data and to acquire data regularly through river terrain survey in order to maintain an active river. The need to build an efficient system have been increased through the enhancement and advancement of River Management Geographic Information Systems(RIMGIS). In this study, database design system and Riverbed Change Data Management Program was developed for systematic management of new river terrain survey data and the efficient use of river data dynamic changes. The key features are construction of river survey data, cross and longitudinal section monitoring and analysis of riverbed change data. Maintenance tasks which can be utilized in river-based architecture was constructed. The expected results are to be able to manage river systematically, and utilization of river topographic survey data efficiently for river maintenance work.KEYWORDS : Bathymetry Data, River-bed Change, Data Management, DB Design, RIMGIS

Flow and Sediment Conditions for the Yellow River Estuary Balance

Multi-object application and water and sediment regulation of the Xiaolangdi Reservoir since 2001 have changed the flow and sediment conditions entering the Lower Reaches of Yellow River and the Estuary. Field flow and sediment data at Lijin Hydrological Station and river cross section elevation data downstream from Lijin Section during 2001~2010 have shown that the Estuary have been in a state of little scouring. The 2D mathematical model has been used to study the flow and sediment conditions for the Yellow River Estuary balance. The conclusions have arrived at that total annual water volume is 196 × 108 m3, total annual sediment volume is 1.40~1.70×108 t, coarse sediment concentration is 3kg/m3.

The Regulation Strategy for Wandering Reach of Zhang River

The wandering reach of Zhang River is improved and regulated during the period 1995-2000. However, after that uncontrolled flow still digress from the control of the river banks, endangering the embankment. This project proposes constructing a canalizing the main course of the river, which could in a short time transform the wandering reach into a bending one. This project would form a compound cross-section of river, consisting the narrow canal and the wide open river beach. This project would easily constrain the main current of river, stabilize the flow regime, and ensure the safety of the embankment. Besides, the hardened and canalized river course would alleviate sediment load to the downstream reach.

The riverine silicon isotope composition of the Amazon Basin

We present here the first large-scale study of riverine silicon isotope signatures in the Amazon Basin. The Amazon and five of its main tributaries were studied at different seasons of the annual hydrological cycle. The δ30Si signature of the dissolved silicon (DSi) exported to the estuary (weighted for DSi flux) for the period considered is estimated at +0.92‰. A river cross-section shows the homogeneity of the Amazon River regarding DSi concentration and isotope ratio. The biogenic silica (BSi) concentration measured in surface water from all rivers is generally small compared to the DSi reservoir but large variations exist between rivers. Very low isotope signatures were measured in the upper Rio Negro (δ30Si=+0.05±0.06‰), which we explain both by an equilibrium between clay formation and dissolution and by gibbsite formation. The Si isotope fractionation in the Andean tributaries and the Amazon main stem can be explained by clay formation and follow either a Rayleigh or a batch equilibrium fractionation model. Our results also suggest that the formation of 2:1 clays induces a fractionation factor similar to that of kaolinite formation.

Efficiency of Flushing through a Sluice-Gated Weir

The four major rivers restoration project (4MRRP) was carried out in Korea between Oct., 2009 and Sep., 2012. The major purposes and effects of the 4MRRP were flood control, safe water security and water quality improvement. For flood control, 450 million m3 of sediments were dredged with the reinforcement of 620 km-long old levees. Sixteen weirs were constructed and 93 reservoir banks were elevated for safe water security. Deformation of the main channels appeared to be inevitable because the longitudinal slope and cross section of the river had changed. In particular the construction of weirs could take the role of sediment detention ponds because the weirs will slow down the velocity and reduce the capability of sediment transportation. Therefore, it is crucial to determine how the siltation phenomena upstream of a weir can be fixed. This study examined the sluicing efficiency of the gate operation for the Gumi weir using 2-dimensional numerical simulations.

Endogenous Water System Pollution Kuznets Curve in China

Based on the data of river cross section water quality in China from 2002 to 2011, we analyze the interrelationship between economic growth and water pollution. The results reveal that water environment will deteriorate with economic growth currently. Openness has no significant effect on pollution. Pollution heaven hypothesis is not true due to environmental regulation. Positive structure effect relies heavily on the substitution of industry. Excellence in environment quality brings more tolerance of exhaustion than productivity to economic growth.

Ship-Generated Waves and Induced Turbidity in the Göta Älv River in Sweden

Ship-generated waves were investigated in the Gota alv river, which is a major waterway on the Swedish west coast between the sea and Lake Vanern. Ships with a typical size of 85x15x5 m (lengthxwidthxdraft) travel at speeds between 5 and 10 knots, generating waves that cause sediment transport and erosion along the river bed and banks. Field measurements of the wave properties and turbidity were carried out during 17 ship passages, and comparisons were made with the most commonly used formulas for predicting ship waves. The formula proposed by the Permanent International Association of Navigation Congresses yielded the overall best agreement for the divergent (secondary) waves, whereas the drawdown (primary wave) could best be estimated from the vessel sinkage. The maximum recorded turbidity was mainly a function of the drawdown, and it could be well predicted from the parameterized bed shear stress. In conclusion, ship waves often induce bed and bank erosion in restricted waterways and, although simplistic formulas involve significant uncertainties, they are still useful tools for predictions. However, more studies are needed to determine the influence of a limited river cross section on the wave generation and the relationship between ship waves and sediment transport. (Less)

Using radar altimetry to update a large-scale hydrological model of the Brahmaputra river basin

Measurements of river and lake water levels from space-borne radar altimeters (past missions include ERS, Envisat, Jason, Topex) are useful for calibration and validation of large-scale hydrological models in poorly gauged river basins. Altimetry data availability over the downstream reaches of the Brahmaputra is excellent (17 high-quality virtual stations from ERS-2, 6 from Topex and 10 from Envisat are available for the Brahmaputra). In this study, altimetry data are used to update a large-scale Budyko-type hydrological model of the Brahmaputra river basin in real time. Altimetry measurements are converted to discharge using rating curves of simulated discharge versus observed altimetry. This approach makes it possible to use altimetry data from river cross sections where both in-situ rating curves and accurate river cross section geometry are not available. Model updating based on radar altimetry improved model performance considerably. The Nash–Sutcliffe model efficiency increased from 0.77 to 0.83. Real-time river basin modelling using radar altimetry has the potential to improve the predictive capability of large-scale hydrological models elsewhere on the planet.

낙동강 하류 하천구조물 건설 전후의 충적층 지하수위 시계열 특성 비교

보의 건설 및 하천 단면의 증가는 하천 수위 상승과 호우기 유출량의 증가를 가져왔다. 낙동강 중하류에 설치된 23개의 지하수 관측망 지하수위 자료를 사용하여 보 담수 전후의 지하수위 시계열 변동 유형의 변화를 분석하였다. 월평균 지하수위 자료를 토대로 담수 전후의 지하수위를 비교한 결과 보의 직상류 주변 지역에서 지하수위 변동이 가장 크게 나타났으며, 8월의 경우 하천 수위 조절 효과로 월평균 지하수위가 0.1 m 감소하였으나 10월에는 1.3 m 상승한 것으로 나타났다. 지하수위 시계열 자료와 하천 수위 자료를 사용하여 군집분석을 실시한 결과, 담수 이전에는 7개 지하수 관측망의 자료가 하천 수위와 유사성 거리가 가까운 그룹이었으나, 담수 이후에는 14개로 증가하여 하천 수위와 유사한 그룹의 범위가 넓어졌다. 지하수위 시계열에 대한 주성분분석 결과, 담수 이전에는 하천 변동성을 대표하는 주성분(주성분 1과 주성분 2)의 설명력이 총 82%이었으나, 담수 이후에는 하천 변동성을 설명하는 주성분(주성분 1)의 설명력이 45%로 줄어들어 지하수위 자료를 설명하는데 하천 요인의 기여도가 줄고 인위적인 양수 등과 같은 기타 요인의 기여도가 높아졌다. 이와 같이 변화되는 수문 환경에 대비하여 지속적인 조사 및 관측이 필요하며, 하천 주변에서는 지표수와 연계되는 지하수 관리 정책이 수립될 필요가 있다. Increasing the river cross-section by barrage construction causes rises in the average river water levels and discharge rates in the rainy season. The time series patterns for groundwater levels measured at 23 riverside monitoring wells along the lower Nakdong River are compared for two cases: before and after water-filling at the Changnyeong-Haman Barrage. Monthly average groundwater levels indicate a distinct increase in groundwater levels in the upstream riverside close to the barrage. River-water level management by barrage gate control in August, during the rainy season, resulted in a 0.1 m decrease in groundwater levels, while water-filling at the barrage in December caused a 1.3 m increase in groundwater levels. The results of hierarchical cluster analysis indicate that seven groundwater monitoring wells and river water levels were in the same group before barrage construction, but that this number increased to 14 after barrage construction. Principal component analysis revealed that the explanation power of two principal components corresponding to river fluctuation, PC1 and PC2, was approximately 82% before barrage construction but decreased to 45% after construction. This finding indicates that the effect of the river level component that contributes to change in groundwater level, decreases after barrage construction; consequently, other factors, including groundwater pumping, become more important. Continuous surveying and monitoring is essential for understanding change in the hydrological environment. Water policy that takes groundwater-surface water interaction into consideration should be established for riverside areas.

Assessment of GeoEye-1 stereo-pair-generated DEM in flood mapping of an ungauged basin

A very high resolution (VHR) digital elevation model (DEM) is produced from a GeoEye-1 0.5-m-resolution satellite stereo pair and is used for floodplain management and mapping applications such as watershed delineation and river cross-section extraction. For this purpose, a 2 m × 2 m resolution terrain surface is produced from the stereo pair by using the Leica Photogrammetry Suite (LPS) enhanced Automatic Terrain Extraction (eATE) algorithm. DEM accuracy is assessed by comparison with measured individual ground control points (GCPs), stream cross-sections and other landscape features. Results show that the produced DEM is in good agreement with ground truth and superior to products of lower resolution, such as 90 m NASA Shuttle Radar Topography Mission (SRTM) and 1:5,000 topographical maps. One- and two-dimensional hydraulic models are used to simulate rainfall–runoff characteristics and flood wave kinematics of the flash flood event of 17 October 2006 that occurred in the ungauged basin of Almirida, using the 2 m VHR-DEM as an input. Results show that the hydraulic simulation based on the generated VHR-DEM, calibrated and validated via field data, produces an accurate extent and water level of the flooded area. Remote sensing stereo reconstruction is a promising alternative to traditional survey methods in flood mapping applications.

An entropy-based method for determining the flow depth distribution in natural channels

A methodology for determining the bathymetry of river cross-sections during floods by the sampling of surface flow velocity and existing low flow hydraulic data is developed . Similar to Chiu (1988) who proposed an entropy-based velocity distribution, the flow depth distribution in a cross-section of a natural channel is derived by entropy maximization. The depth distribution depends on one parameter, whose estimate is straightforward, and on the maximum flow depth. Applying to a velocity data set of five river gage sites, the method modeled the flow area observed during flow measurements and accurately assessed the corresponding discharge by coupling the flow depth distribution and the entropic relation between mean velocity and maximum velocity. The methodology unfolds a new perspective for flow monitoring by remote sensing, considering that the two main quantities on which the methodology is based, i.e., surface flow velocity and flow depth, might be potentially sensed by new sensors operating aboard an aircraft or satellite.