Determination of minimum flood flow for regeneration of floodplain forest from inundated forest width-stage curve

Floods are essential for the regeneration and growth of floodplain forests in arid and semiarid regions. However, river flows, and especially flood flows, have decreased greatly with the increase of water diversion from rivers and/or reservoir regulation, resulting in severe deterioration of floodplain ecosystems. Estimation of the flood stage that will inundate the floodplain forest is necessary for the forest＇s restoration or protection. To balance water use for economic purposes and floodplain forest protection, the inundated forest width method is proposed for estimating the minimum flood stage for floodplain forests from the inundated forest width-stage curve. The minimum flood stage is defined as the breakpoint of the inundated forest width-stage curve, and is determined directly or analytically from the curve. For the analytical approach, the problem under consideration is described by a multi-objective optimization model, which can be solved by the ideal point method. Then, the flood flow at the minimum flood stage （minimum flood flow）, which is useful for flow regulation, can be calculated from the stage-discharge curve. In order to protect the forest in a river floodplain in a semiarid area in Xinjiang subject to reservoir regulation upstream, the proposed method was used to determine the minimum flood stage and flow for the forest. Field survey of hydrology, topography, and forest distribution was carried out at typical cross sections in the floodplain. Based on the survey results, minimum flood flows for six typical cross sections were estimated to be between 306 m3/s and 393 m3/s. Their maximum, 393 m3/s, was considered the minimum flood flow for the study river reach. This provides an appropriate flood flow for the protection of floodplain forest and can be used in the regulation of the upstream reservoir.

Numerical Simulation of Dam-Break Flows Using Radial Basis Functions: Application to Urban Flood Inundation

Dam-break flows pose significant threats to urban areas due to their potential for causing rapid and extensive flooding. Traditional numerical methods for simulating these events struggle with complex urban landscapes. This paper presents an alternative approach using Radial Basis Functions to simulate dam-break flows and their impact on urban flood inundation. The proposed method adapts a new strategy based on Particle Swarm Optimization for variable shape parameter selection on meshfree formulation to enhance the numerical stability and convergence of the simulation. The method’s accuracy and efficiency are demonstrated through numerical experiments, including well-known partial and circular dam-break problems and an idealized city with a single building, highlighting its potential as a valuable tool for urban flood risk management.

Assessment of Storm Surge and Flood Inundation in Chittagong City of Bangladesh Based on ADCIRC and GIS

Coastal flooding caused by tropical cyclones has long been a major threat to life,property,and infrastructure in coastal zones.This study assessed the risk of flooding in Chittagong,southeastern Bangladesh,under extreme sea level scenarios caused by high astronomical tides and storm surges.The Jelesnianski typhoon model and the ADvanced CIRCulation hydrodynamic model were used to simulate 91 typhoons that occurred in the Bay of Bengal between 1981 and 2017,and observational data were used for model validation.The inundation model was based on a digital elevation model and a seed spread algorithm,and a geographical information system was used to visualize the flood risk.Under four scenarios,the changes in flood levels caused by sea level rise had no signifi-cant influence on the extent of flooding in Chittagong.At flood levels of 8.82m(50-year storm surge without sea level rise)and 8.89 m(50-year storm surge with sea level rise),the maximum estimated area of inundation was 11.35 km^(2).The western coastal and southeastern river coastal plain areas of Chittagong have the highest risk of inundation due to their low-lying terrain.At flood levels of 9.83m(100-year storm surge without sea level rise)and 9.97m(100-year storm surge with sea level rise),the maximum simulated flood extent was 36.44km^(2).Simulated floodwaters propagated in a south–north direction,and most of the northern areas of the city are at risk of inundation under these scenarios.

Flood risk assessment of check dams in the Wangmaogou watershed on the Loess Plateau of China

Check dams have been widely used in China’s Loess Plateau region due to their effectiveness in erosion and flood control.However,the safety and stability of the check dam decrease with the operation process,which increases the probability of dam failure during flood events and threatens local residents’ life and property.Thus,this study simulated flood process of the check dam failure in the Wangmaogou watershed in Yulin City,Shaanxi Province,China,calculated different types of inundation losses based on the flood inundation area within the watershed,and determined the number of key flood protection check dams by classifying the flood risk levels of the check dams.The results showed that 5 dams in the watershed were subject to overtopping during different rainfall return periods,which was related to their flood discharge capacity.Dam failure flood process showed a rapid growth trend followed by slow decrease,and the time of flood peak advanced with increase in the return period.After harmonization of evaluation scales,the magnitude of flood inundation losses can be ranked as:economic losses(212.409 million yuan) > life losses(10.368 million yuan) > ecological losses(6.433 million yuan).The risk value for both individual dams and the whole dam system decreases as the return period increases.The number of key flood protection check dams in the Wangmaogou watershed was 2,3,3,3,4,and 5 for floods with return periods of 10,20,30,50,100,and 200 years,respectively.The results provided a theoretical basis for the safe operation and risk evaluation of check dams in the Loess Plateau Hills watershed.

Effect of nitrogen and phosphorus on the water quality in the Three Gorges Reservoir Area during and after its construction

A survey concerning the concentration of the nutrients in the Three Gorges Reservoir Area was carried out. This paper presents the parameters(NO 3 - N, NO 2 - N, Kjeldahl N, non ionic ammonia, P PO 4 and TP) determined at 16 sampling sites from 1997 to 1999 The dominant soluble nitrogen form was NO 3 - N followed by Kjeldahl N, NO 2 - N and non ionic ammonia. Mean values of NO 3 - N, NO 2 - N, Kjeldahl N and non ionic ammonia ranged from 0 50 to 2 37 mg/L, 0 022 to 0 084 mg/L, 0 33 to 0 99 mg/L and 0 007 to 0 092 mg/L respectively. Mean values of P PO 4 at most sampling sites were higher than 0 1 mg/L for subject to eutrophication. The major factors influencing the concentrations of N and P might be agricultural runoff, municipal and industrial effluents. In addition, 6 kinds of soil were sampled at the area where would inundated after the dam completed. Two approaches were adopted to simulate the N and P release from the inundated soils. The results showed that the soils would release nitrogen and phosphorus to the overlying water when the soils were inundated. The characteristics of soil affected the equilibrium concentrations of N and P between the soil and the overlying water.

A general multi-objective programming model for minimum ecological flow or water level of inland water bodies

Assessment of ecological flow or water level for water bodies is important for the protection of de- graded or degrading ecosystems caused by water shortage in arid regions, and it has become a key issue in water resources planning. In the past several decades, many methods have been proposed to assess ecological flow for rivers and ecological water level for lakes or wetlands. To balance water uses by human and ecosystems, we proposed a general multi-objective programming model to determine minimum ecological flow or water level for inland water bodies, where two objectives are water index for human and habitat index for ecosystems, respectively Using the weighted sum method for multi-objective optimization, minimum ecological flow or water level can be determined from the breakpoint in the water index-habitat index curve, which is similar to the slope method to de- termine minimum ecological flow from wetted perimeter-discharge curve. However, the general multi-objective programming model is superior to the slope method in its physical meaning and calculation method. This model provides a general analysis method for ecological water uses of different inland water bodies, and can be used to define minimum ecological flow or water level by choosing appropriate water and habitat indices. Several com- monly used flow or water level assessment methods were found to be special cases of the general model, including the wetted perimeter method and the multi-objective physical habitat simulation method for ecological river flow, the inundated forest width method for regeneration flow of floodplain forest and the lake surface area method for eco- logical lake level. These methods were applied to determine minimum ecological flow or water level for two repre- sentative rivers and a lake in northern Xinjiang of China, including minimum ecological flow for the Ertix River, minimum regeneration flow for floodplain forest along the midstream of Kaxgar River, and minimum ecological lake level for the Ebinur Lake. The results illustrated the versatility of the general model, and can provide references for water resources planning and ecosystem protection for these rivers and lake.

基于多项式逼近的固定式平台响应谱理论研究

依据波浪力成因和作用效果的不同,将波浪力分为两部分(Morisson波浪力和Inundation波浪力)讨论。对于两种波浪力中的非线性拖曳力项,采用高次多项式逼近,结合高斯型统计量高阶矩计算原理、相关函数、变换法和单输入多输出系统的互谱关系,预测海流海浪联合作用下的海洋平台响应谱的理论形式,求得总波浪力谱以及平台响应谱。在Inundation模态力的相关函数推导过程中,考虑海流影响时,惯性力项PI与拖曳力项PD的相关函数总和为0,这一结果与不考虑海流影响时的结果相同。

Study on the damage of the “91．7” rainstorm in Sihu drainage area with remote sensing application technique

In this paper, the water equilibrium and ground truth are analyzed for '91.7' rainstormin Sihu drainage area, Hubei Province, China. The flood and waterlogging situation of ' 91.7'rainstorm in this area are investigated using remote sensing, especially the estimation of inundatedarea, the analysis of temporal and spatial characters of this flood and waterlogging damage. Andthe way of flood-trace using remote sensing is explored. At last, the disastroiis conditions are evalu-ated.

Prediction of Debris-flow Danger Area by Combining Hydrological and Inundation Simulation Methods

Debris flows have caused serious human casualties and economic losses in the regions strongly affected by the Ms8.0 Wenchuan earthquake of 2oo8. Debris flow mitigation and risk assessment is a key issue for reconstruction. The existing methods of inundation simulation are based on historical disasters and have no power of prediction. The rain- flood method can not yield detailed flow hydrograph and does not meet the need of inundation simulation. In this paper, the process of water flow was studied by using the Arc-SCS model combined with hydraulic method, and then the debris flow runoff process was calculated using the empirical formula combining the result from Arc-SCS. The peak discharge and runoff duration served as input of inundation simulation. Then, the dangerous area is predicted using kinematic wave method and Manning equation. Taking the debris flow in Huashiban gully in Beichuan County, Sichuan Province, China on 24 Sep. 2oo8 as example, the peak discharge of water flow and debris flow were calculated as 35.52 m3·s-1 and 215.66 m3·s-, with error of 4.15% compared to the measured values. The simulated area of debris-flow deposition was 161,500 m2, vs. the measured area of 144,097 m2, in error of 81.75%. The simulated maximum depth was 12.3 m, consistent with the real maximum depth between lO and 15 m according to the field survey. The minor error is mainly due to the flow impact on buildings and variations in cross-section configuration. The present methodology can be applied to predict debrisflow magnitude and evaluate its risk in other watersheds inthe earthquake area.

Numerical Study of Storm Surge Inundation in the Southwestern Hangzhou Bay Region During Typhoon Chan-Hom in 2015

Storm surge inundation is a major concern in marine hazard risk assessment during extreme weather conditions.In this study,a high-resolution coupled model(the ADVanced CIRCulation model+the Simulating WAves Nearshore model)was used to investigate the storm surge inundation in the southwestern Hangzhou Bay region during Typhoon Chan-hom in 2015.The simulated hydrodynamic processes(sea surface wave and storm tide)were validated with measured data from wave buoys and tide gauges,indicating that the overall performance of the model was satisfactory.The storm surge inundation in the coastal area was simulated for several idealized control experiments,including different wave effects(wave-enhanced wind stress,wave-enhanced bottom stress,and wave radiation stress).Dike overflowing cases with different dike heights and dike breaking cases with different dike breach lengths were considered in the simulation.The results highlight the necessity of incorporating wave effects in the accurate simulation of storm surge inundation.Dike height significantly influences the magnitude and phase of the maximum inundation area in the dike overflowing cases,and dike breach length is an important factor impacting the magnitude of the maximum inundation area in the dike breaking cases.This study may serve as a useful reference for accurate coastal inundation simulation and risk assessment.

Identification of Inundation Hazard Zones in Manas Basin, China, Using Hydrodynamic Modeling and Remote Sensing

A two-dimensional hydrodynamic model, Floodarea was applied to simulate the flood inundation area and flood depth in Manas basin, China. Two scenes of Landsat TM images were also used in this research. One image was used to produce the spatial distributed manning roughness to feed the model, the other one was used to delineate the actual inundated area by a modified NDWI method. The model and the manning roughness were validated by the comparison of simulated flood inundation extent and the corresponding actual inundated area obtained from Landsat image. The results show that the actual inundation extent obtained from Landsat image was 240.45 km2, and the modeled inundation area was276.15 km2. It indicates that manning roughness ranging from 0.025 to 0.833 is appropriate in the basin. In addition, the modeled flood depth varied from 0 to7.77 m. Taking land use into account, five hazard zones were identified in the study area. This study would be beneficial to flood control and disaster reduction.

A High Resolution Forecast Model of Storm Surge Inundation

In order to forecast storm surge inundation, a two-dimensional model is established. In the model, an alternating computation sequence method is used to solve the governing equations, and the dry and wet method is introduced to treat the moving boundary. This model is easy to use. It has a friendly input interface and Arcview GIS is used as the output interface. The model is applied to the Shantou area to simulate the storm surge elevations and inundations caused by Typhoons 6903 ane 0104 using the same relevant parameters. The calculated results agree well with the observations.

Possibilities of urban flood reduction through distributed-scale rainwater harvesting

Urban flooding in Chittagong City usually occurs during the monsoon season and a rainwater harvesting(RWH)system can be used as a remedial measure.This study examines the feasibility of rain barrel RWH system at a distributed scale within an urbanized area located in the northwestern part of Chittagong City that experiences flash flooding on a regular basis.For flood modeling,the storm water management model(SWMM)was employed with rain barrel low-impact development(LID)as a flood reduction measure.The Hydrologic Engineering Center's River Analysis System(HEC-RAS)inundation model was coupled with SWMM to observe the detailed and spatial extent of flood reduction.Compared to SWMM simulated floods,the simulated inundation depth using remote sensing data and the HEC-RAS showed a reasonable match,i.e.,the correlation coefficients were found to be 0.70 and 0.98,respectively.Finally,using LID,i.e.,RWH,a reduction of 28.66%could be achieved for reducing flood extent.Moreover,the study showed that 10%e60%imperviousness of the subcatchment area can yield a monthly RWH potential of 0.04e0.45 m3 from a square meter of rooftop area.The model can be used for necessary decision making for flood reduction and to establish a distributed RWH system in the study area.

An experimental study on tsunami inundation over complex coastal topography

In recent studies, the effects of complex costal topography on tsunami run-up has sparked heated discussion. This study mainly aims at investigating the effects of complex costal topography on the tsunami inundation distance and the effectiveness of sand dunes in dissipating tsunami wave energy. The experiments were carried out in a wave flume to investigate the potential reduction effects of wave run-up by non erodible sand dune like features. The results show that increasing dunes spacing could not significantly affect inundation distance. However, if the height of sand dunes is of the same order of magnitude as the incoming tsunami wave and the gaps between the dunes are large enough, successful tsunami mitigation could also be possible.

The Physico-Chemical Water Quality of the Obafemi Awolowo University Teaching and Research Farm Lake, O.A.U. Campus, Ile-Ife, Southwest, Nigeria

The physico-chemical water quality of the Obafemi Awolowo University Teaching and Research Farm Lake, Ile-Ife, Nigeria, was studied over an annual cycle (September 2006 to August 2007) almost 40 years after its impoundment in 1967. This was with a view to obtaining the then current state of physico-chemical water quality parameters with their variations in time and space as well as using some of the data obtained to evaluate the aging process of the lake for the 40 years of its existence. There was no significant (p > 0.05) horizontal variation (i.e. upstream-dowstream) in the physico-chemical characteristics of the lake whereas, Apparent-color, True color, Turbidity, Total Suspended Solids (TSS), Total Solids (TS) and Total Acidity increased significantly (p < 0.05) from the lake surface towards the bottom of the lake. On the other hand, water pH, Dissolved Oxygen (DO);Dissolved Oxygen Saturation (DO% Sat.) and Biochemical Oxygen Demand (BOD5) decreased significantly (p < 0.05) from the lake surface towards the bottom of the lake. Dissolved Oxygen (DO), Dissolved Oxygen Saturation (DO% Sat.) and Nitrate ion (NO-3) were significantly higher (p < 0.05) in the dry season than in the rainy season while, True colour, pH, Conductivity, Total Hardness, Calcium ion (Ca2+), Magnesium ion (Mg2+), Potassium ion (K+) and Sulphate ion (SO2-4) were significantly higher (p < 0.05) in the rainy season than in the dry season. The lake water could be regarded as shallow, coloured, turbid, less transparent, slightly acidic, soft and well-buffered fresh-waterbodies with evidence of aging (i.e. transforming the lake from an oligotrophic status to a eutrophic waterbody). The results indicated that the lake is suitable for most of its applications with little or no adjustments as the case may be;except probably for drinking purposes where some microbial analysis may be necessary.

Floodplain Mapping of Nashwaak River,Canada:An Assessment Based on High-Resolution Hydraulic Simulation

Recent advances in hydraulic modeling create improved methodology to accurately predict the extent of floodplain map in order to assist policy makers to develop flood hazard mitigation measures and timely inform the local communities with the flood risk alerts.However,accurate prediction of the inundation map also depends on the spatial resolution of the topographic data.In this study,we developed a novel high-resolution modeling framework for Nashwaak River watershed,New Brunswick,Canada to capture significant flooding along the banks of the river for the two historic flood events and accurately map the floodplains for both the gauged and ungauged areas of the watershed.The model is based on HEC-RAS(US Army Corps of Engineers Hydrologic Engineering Center River Analysis System)hydraulic model and the topographic data were generated from high-resolution LiDAR data of~0.5 m.The model runs were driven by observed flow conditions applied at the boundary and the framework is based on different spatial resolution to determine the effect of spatial resolution on the predicted inundation.We validated the model simulated water surface elevation with the observed data and the model reproduces reasonably good skill score.Results from the numerical simulation suggest that apart from the strength of the stream velocity,design of the modeling framework plays an important role in determining the inundation depth as well as the maximum flooding extent.

Experimental Study of Condensation Heat Transfer on Tube Bundles in Large Power Plant Condensers

In order to clarify the effect of condensate inundation on steam condensation in a large tube bundle, condensation heat transfer and the condensate flow pattern in the tube bundle have been experimentally investigated. Test tube bundle consists of 36 cooling tubes, 12 condensate supply tubes and 24 un-cooled dummy tubes. Cooling test tubes are made of copper and have an outer diameter of 19.1 mm and condensing length of 150 mm, Steam flows horizontally through the test tube bundle at gap velocities 15-27 m/s at pressures of 8.8 kPa. In this study, experimental data about condensate flow pattern and condensation heat transfer in a tube bundle were collected for the optimization of tube arrangement in large power plant condensers.

Inundation Studies Along the East Coast of India due to Tsunamigenic Earthquakes in North-Andaman and Car Nicobar Subduction zone

The Sumatra-Andaman arc is an active subduction zone and had generated several destructive Tsunamis in the past.In this paper we have analyzed two historical Tsunamigenic earthquakes from this region. One of the historical earthquake is the earthquake of 26th June 1941 in the North Andaman region,which was one of the strongest in the Andaman Sea and Bay of Bengal of magnitude M_w=7.7.This earthquake had triggered tsunami which affected the east coast of India.The other is the earthquake in Car Nicobar region on 31 st December 1881 of magnitude M_w=7.9. This submarine earthquake beneath the

Evaluation of Impacts of Sea Level Rise on the Coast of Mohammedia(Morocco):Land at Risk of Flooding and Socioeconomic Impacts

One of the significant consequences of the climate change predicted for the next decades is the sea and ocean level rise.The coastal zone of Mohammedia (Morocco),a site of significant socio-economic activeties largely open to the Atlantic Ocean,is thus confronted with hydrodynamic agents and a possible sea level rise,whose impacts will result in an immersion of the low topography areas。

Numerical simulations of the coastal effects of tsunami waves caused by the 1993 Hokkaido-Nansei-Oki earthquake

Generally,tsunami waves become hazardous only when approaching the coast.Studying the runup and inundation of tsunami waves is important for understanding the tsunami evolution and for tsunami hazard assessment.Here,we simulated the 1993 Hokkaido-Nansei-Oki(HNO) tsunami using a finite-difference model based on nonlinear shallow-water equations.We focused on the runup and inundation of tsunami wave propagation onto coastal area of Okushiri Island near Hokkaido,Japan,and investigate the relationship of different runup heights with the morphology and bathymetry of the seashore.In the simulation,a nested 4-layer grid system and moving boundary technique are adopted to study runup and inundation.The calculated tsunami heights and inundations in the region agreed well with field measurements.The local bathymetric and topographic characteristics had a first-order effect on the runup.Numerical experiments show that the focusing of certain local bathymetric features would amplify both wave height and current velocity remarkably.The results show that computation on dense grids is necessary to reproduce the observed runup heights,and inundation velocity is an important factor preventing tsunami devastation.In addition,we discussed the potential capability of sediment transport to illustrate the impact of tsunami waves on coastal geomorphology.