Effect of Flood Peak Discharge Control by a Small Reservoir in an Urbanized Area—Case Study in the Kurabe River Basin, Japan

Recently severe damage of flooding by urbanization was frequently occurred. To prevent this damage, small reservoir was constructed in the urbanized residential area. This paper describes an effect of flood peak discharge control by a small reservoir (control reservoir) caused by rapidly developed urbanization. Although work for this purpose was conducted, research on the effects of the control reservoir was not conducted until now. This research, conducted by simulation, was a case study in the Kurabe River Basin in the Tedori River Alluvial Fan Area, Japan, based on the precise investigation of the reservoir in the actual field. The study was conducted to determine not only the actual control reservoir capacity for the newly developed residential area but also the ideal capacity for all present residential areas and the largest capacity allowable for a maximum rainfall event that recently occurred. The control reservoir effects between individual blocks and the entire basin area were compared by dividing the test basin into 15 blocks (sub-basins). The results showed that the effects on the capacity per unit area of the residential area in blocks have close relationship with the decreasing ratio of peak discharge in blocks. Consequently, the effects of control reservoir capacity and the limitation were clarified. In the future, control reservoirs should be constructed for all of the already developed residential areas, for example, by utilizing underground car parking lot. The results of this research can contribute to the design of the control reservoir for protection against flooding damage in urbanized areas.

Analysis of the effect of regional lateral inflow on the flood peak of the Three Gorges Reservoir

The Three Gorges Region(TGR),located at the lower reach of the Upper Yangtze River Basin(UYRB) in China,suffers from heavy rainstorm frequently.The runoff generated from TGR composes an important part of the total flood at the famous Three Gorges Reservoir(TGRe).During the severe flood period in 1954,for example,the water from TGR accounted for up to 13.2% of the 30-days maximum flood volume of the UYRB.Considering the short and steep tributaries with rapid concentration,the regional lateral inflow(RLI) may induce more serious effect on the flood peak of the TGRe than the volume.However,hydrological data of the sparse gauge stations is too insufficient to evaluate the effect of RLI.This paper studied the impact by analyzing 880 flood events during 1956-2000.By comparing the observed hydrograph and simulated hydrograph with HEC-RAS software regarding no RLI,the effect of RLI on flood peak value and timing properties was identified and quantified.The variability of this effect among floods of different magnitudes was also analyzed.To evaluate the analysis uncertainty associated with the parameter of roughness coefficient,four sets of roughness coefficients from different research groups were employed in this study.The results showed that RLI contributes discharge of 3524 m3/s to flood peaks of the TGRe on average,with the contribution ratio of 15.9%.RLI contributes 12000 m3/s to the flood peaks larger than 50000 m3/s on average,with 25000 m3/s as its upper bound,while the contribution ratio can reach up to 50%,with an average of 20%.The variability of this effect is great among different events.Statistical analysis showed that to larger flood peak of the TGRe,RLI contributes more discharge with higher variability,and the contribution ratio and its variability are slightly larger,and events with higher contribution ratio occur more frequently.RLI can reshape the hydrograph,leading to earlier appearance of flood peak.This effect and its variability increase with the contribution ratio.This study has revealed that RLI plays an important role in large flood peak of the TGRe,which calls for more reliable flood forecasting methods to prolong the forecast lead time and improve the accuracy for the safety of the Three Gorges Dam and the protection of its lower reaches during severe flood disaster period.

Responses of flood peaks to land use and landscape patterns under extreme rainstorms in small catchments-A case study of the rainstorm of Typhoon Lekima in Shandong,China

Investigations of the formation mechanisms of flood peaks in small catchments facilitate flood prediction and disaster prevention under extreme rainstorms.However,there have been few studies on the re-sponses of flood peaks to land use landscape patterns using field surveys during extreme rainstorm events.Based on field data from 17 small catchments near the rainstorm center of Typhoon Lekima,7 landscape indices were chosen.The flood peak and its sensitivity to the land use landscape were investigated by combining remote sensing interpretation and related analysis.The conclusions are as follows:(1)The peak discharge of the small catchment was 2.36e56.50 m3/s,the peak modulus was 8.00 e48.89 m3/(s$km2),and the flood index K ranged from 3.61 to 4.55.(2)Under similar rainfall conditions,the flood peak modulus,K and the proportion of sloping cropland had significantly positive correlations(p<0.05).The flood peak modulus was significantly negatively correlated with the proportion of forest-grassland and terrace(p<0.05),and K and the proportion of forest-grassland and terraced land exhibited a negative correlation.(3)The flood peak modulus and K were positively correlated with the landscape fragmentation.(4)The sensitivities of small catchments to floods were evaluated to be moderate compared to K values from other studies.The ability of small catchments to cope with extreme rain-storms can be improved by increasing the areas of forest-grassland,and terraces and reducing landscape fragmentation.Our results could be applied to provide a basis for land use planning and support for the response against disasters caused by extreme floods.

Three Gorges Project Withstanding 2010 Peak Floods

The Three Gorges Project(TGP) on the Yangtze River(YR) is the largest hydro-power project in the world;it is now attracting the world wide attention.Possessing comprehensive utilization benefits mainly for flood control,power generation and navigation improvement,TGP is a vital and important project in harnessing and developing the YR.The Project primarily aims at flood control whose reservoir has a total storage capacity of 39.3 billion m3,22.15 billion m3 of which can be set for flood control.Construction of the project has greatly improved the flood control capacity in the middle and lower sections of the YR.In 2010 TGP has successfully withstood 3 peak floods,especially the one on July 20 with a frequency of once in 20-year,the largest since the construction of TGP.TGP as an eco-environmental project will be beneficial to ecological and environmental protection and low carbon economy and it will accelerate coordination of the economy,society,resources and environment and sustainable development along the valley,as well as the rapid development of Chinese economy.

Numerical Investigation on Downstream Increase in Peak Discharge of Hyperconcentrated Floods in the Lower Yellow River

Hyperconcentrated floods in the Yellow River usually accompanied with some peculiar phenomena that cannot be explained by general conceptions of ordinary sediment-laden flow (e.g., downstream increase in peak discharge, instability flow, ripping up the bottom). Up to date, the mechanisms for the abnormal phenomena are not well understood. The aim of this paper is to facilitate a new insight into the abnormal downstream increase in peak discharge of hyperconcentrated floods in the lower Yellow River. Numerical model experiments have been conducted on a typical flood occurred in August 1992 in the Lower Yellow River during which the peak discharge at Huayuankou station was 1690 m3/s larger than the value at Xiaolangdi station at upstream. It is found that a fully coupled model that incorporates the contribution of bed evolution to the mass conservation of the water-sediment mixture, can reasonably well capture the characteristics of peak discharge rise and severe bed scour, while separate numerical experiment using a decoupled model, which ignores the feedback effects of bed evolution, shows no rise in the peak discharge. This leads us to comment, if only briefly, that the entrainment of sediment due to bed erosion is the main reason for causing peak discharge increase along downstream course.

Application and comparison of coaxial correlation diagram and hydrological model for reconstructing flood series under human disturbance

Intense human activities have greatly changed the flood generation conditions in most areas of the world, and have destroyed the consistency in the annual flood peak and volume series. For design flood estimation, coaxial correlation diagram and conceptual hydrological model are two frequently used tools to adjust and reconstruct the flood series under human disturbance. This study took a typical mountain catchment of the Haihe River Basin as an example to investigate the effects of human activities on flood regime and to compare and assess the two adjustment methods. The main purpose is to construct a conceptual hydrological model which can incorporate the effects of human activities. The results show that the coaxial correlation diagram is simple and widely-used, but can only adjust the time series of total flood volumes. Therefore, it is only applicable under certain conditions(e.g. There is a strong link between the flood peaks and volumes and the link is not significantly affected by human activities). The conceptual model is a powerful tool to adjust the time series of both flood peak flows and flood volumes over different durations provided that it is closely related to the catchment hydrological characteristics, specifically accounting for the effects of human activities, and incorporating expert knowledge when estimating or calibrating parameters. It is suggested that the two methods should be used together to cross check each other.

FLOOD ROUTING MODELS IN CONFLUENT AND DIVIDING CHANNELS

By introducing a water depth connecting formula, the hydraulic equations in the dividing channel system were coupled and the relation of discharge distribution between the branches of the dividing channels can be yielded. In this manner, a numerical model for the confluent channels was established to study the variation of backwater effects with the parameters in the channel junction. The meeting of flood peaks in the mainstream and tributary can be analyzed with this model.The flood peak meeting is found to be a major factor for the extremely high water level in the mainstream during the 1998 Yangtze River flood. Subsequently the variations of discharge distribution and water level with channel parameters between each branch in this system were studied as well. As a result, flood evolution caused by Jingjiang River shortcut and sediment deposition in the entrance of dividing channels of the Yangtze River may be qualitatively elucidated.It is suggested to be an effective measure for flood mitigation to enhance regulation capability of reservoirs available upstream of the tributaries and harness branch entrance channels.

Impacts of water surface area of watershed on design flood

In order to analyze the impact of the water surface area of a watershed on the design flood, the watershed was classified into a land watershed and a water surface watershed for flood flow calculation at the same time interval. Then, the design flood of the whole watershed was obtained by adding the two flood flows together. Using this method, we calculated design floods with different water surface areas of three reservoirs and analyzed the impact of water surface area on the flood volume and peak flow. The results indicate that larger water surface areas lead to greater impacts on the flood volume and peak flow. For the same watershed area, the impact of water surface area on the flood volume and peak flow is positively proportional to the flood frequency, i.e., the higher the frequency, the greater the impact becomes.

STUDY ON THE FREQUENCY AND PRINCIPLE OF FLOOD CATASTROPHE IN THE CHANGJIANG DELTA AND ITS NEIGHBORING REGIONS IN THE LAST 2000 YEARS

Documented materials, especially those about flooding catastrophe, are abundant comprehensive and well-preserved, which makes possible the systematical collection of materials about historical document about climate evolution in Changjiang (Yangtze) Delta region and its neighboring areas. We make good use of the exceptional information to discuss the genesis and principle of flooding in this region. Analysis shows that the main flooding periods in the studied region in the last 2000 years were the Western Jin Dynasty, Eastern Jin Dynasty, Northern and Southern Dynasties, Southern Song Dynasty, Yuan Dynasty, Ming Dynasty and Qing Dynasty. The periods with flooding peak values were the 4th century, 5th century, 7th century, 9th century, early 12th century, early 14th century, mid-15th century, and early 18th century A.D. Possibility of reappearance of flooding peak value in the early 21st century will be great, and the hazard prevention and the hazard reduction will be still hard.

Development of Upstream Data-Input Models to Estimate Downstream Peak Flow in Two Mediterranean River Basins of Chile

Accurate flood prediction is an important tool for risk management and hydraulic works design on a watershed scale. The objective of this study was to calibrate and validate 24 linear and non-linear regression models, using only upstream data to estimate real-time downstream flooding. Four critical downstream estimation points in the Mataquito and Maule river basins located in central Chile were selected to estimate peak flows using data from one, two, or three upstream stations. More than one thousand paper-based storm hydrographs were manually analyzed for rainfall events that occurred between 1999 and 2006, in order to determine the best models for predicting downstream peak flow. The Peak Flow Index (IQP) (defined as the quotient between upstream and downstream data) and the Transit Times (TT) between upstream and downstream points were also obtained and analyzed for each river basin. The Coefficients of Determination (R2), the Standard Error of the Estimate (SEE), and the Bland-Altman test (ACBA) were used to calibrate and validate the best selected model at each basin. Despite the high variability observed in peak flow data, the developed models were able to accurately estimate downstream peak flows using only upstream flow data.

The Simulation of Flood Hydrograph in Natural and Urban Basins

The exact estimation of the flood is one of the main concerns for designers of the water bodies. The significance of this issue in the catchment areas overlooking the cities is more and more visible. In this study, HEC-HMS model is used to simulate the catchment area of the Khoshk River in the Shiraz city. The simulation results and its comparison with the observations based on Nash-Sutcliffe coefficient confirm the validity of the model. The input data of the model includes Rainfall, Measured Discharge, Flood Peak Time, Curve Number (CN), and so on. These results indicate that although the shape of the simulated hydrograph is not exactly the same as the observed hydrograph, it has estimated the peak of flood discharge well with an error rate of two to five percent.

老油田“3+2”大幅度提高采收率技术内涵、机理及实践

传统方式的化学驱项目一般采取“2+3”的协同方式,也就是先通过水驱井网调整一次到位,再实施化学驱,受剩余油认识和预测精度的影响,会出现部分低产低效井,化学驱含水谷底平台期短,提高采收率幅度有限。为此,胜利油田通过基础攻关和探索实践,创新提出了化学驱与动态优化调整加合增效的“3+2”大幅度提高采收率技术,该技术是指在化学驱过程中,充分发挥和利用驱油体系扩大波及体积、提高驱油效率、调整动态非均质性的特点,主动培育、壮大动态剩余油富集区(“油墙”),适时井网调整、重构流场、均衡注采,高效动用、采出“油墙”,最大程度延长化学驱含水谷底平台期,实现三次采油和二次采油(“3+2”)适配优化、大幅度提高采收率的目的。通过大量物理模拟和数值模拟研究,明确了“井网-驱油剂-剩余油”适配优化提高采收率的机理。该技术在胜坨油田二区东三段5砂组进行了应用,通过优化“3+2”井网调整方式、驱油体系和注入参数等,预计区块含水谷底平台期从3 a延长至8 a,最终采收率为60.5%,比原方案采收率再提高7.5百分点。该技术是老油田大幅度提高采收率的关键技术,可以为中外同类型油藏延长化学驱见效高峰期提供指导和借鉴。

Estimation of Unit Flood Discharge for Various Land Use Types with a Focus on Urbanization

We proposed unit flood discharge model that defined as the discharge into end-order (smallest) drainage canals. The discharge acts an important role for estimating regional flooding by big rainfall events which leading roughly estimation of flood discharge associated with land use changes as urbanization. In some areas of Japan, increased urbanization with insufficient drainage canal capacity has led to increasingly frequent flooding and flood damage. The aim of this study was to investigate the effect of urbanization on unit flood discharge using a runoff model for the Tedori River alluvial fan area, Japan. The discharge was studied as collecting runoff from paddy fields, upland crop fields, and residential lots. A runoff model for various land use types in the study area was developed using actual and physical properties of the runoff sites, and parameters for paddy fields. The model was tested using 54 big events and inputted those. The maximum total runoff ratio among different land use types was observed for residential lots, and the ratio remained relatively constant across different flood events. The minimum total runoff ratio was observed for irrigated paddy fields. There was a positive relationship between the total runoff ratio and total precipitation for all land use types. Whereas, the relationship between the peak runoff ratio and peak precipitation was variable. The runoff analysis was carried out using 60-min and 10-min precipitation data. For agricultural land, data for both intervals produced similar results.

我国发展二氧化碳驱油技术的路径思考

当前,气候变化给人类社会发展带来了严峻的挑战。二氧化碳驱油作为一种能够有效提高油田采收率和减少二氧化碳排放的技术,在保障国家能源安全、创造社会经济价值、实现生态环境目标方面具有重要意义,是我国实现双碳目标的关键手段。在中国,二氧化碳驱油技术已经表现出广阔的应用前景,但是大规模推广应用还需要较长时间;同时,全球低碳合作和能源市场转型为中国发展二氧化碳驱油技术提供了机遇,但是也面临着经济成本高和环境风险大的挑战。今后,中国要全面发展和推广二氧化碳驱油技术,需要从构建产业法律体系、促进技术研发创新、完善合作交流机制、提高环境风险管理等方面持续发力。

稻田控制排水对高邮灌区河道洪水过程的影响

以高邮灌区为例,采用水文-水动力模型,研究稻田控制排水措施对河道洪峰流量、水位和洪水过程的影响。结果表明,雨前通过控制灌溉适当降低田间水位可减轻稻田出流峰值,随着稻田控制水位的增加,稻田径流峰值逐渐降低。通过稻田控制排水,可降低田间出口峰值流量,改变灌区河道洪水过程,降低河道洪峰流量和水位,减轻灌区内部以及附近河道的防洪压力。

有效不透水面分布对城市雨水径流的影响

城市区域不透水面分布错综复杂,汇流路径多样,不透水面有效性及其产流机制成为城市水文学的热点问题。研究以北京市主城区为对象,构建了基于汇水路径的有效不透水面的识别方法,拟合出总不透水面与有效不透水面的经验公式,定量识别了不透水面有效性对北京市主城区雨水径流的影响。结果表明:考虑不透水面有效性能显著提升模型模拟精度,针对不同城市化阶段,在各种重现期降雨情景下设置不同有效不透水面比例并进行模拟,发现有效不透水面对低重现期降雨产流过程的影响远大于高重现期降雨产流过程,且城市化前期有效不透水面增加会导致较大洪峰增长率,而城市化后期影响减小。研究可为优化城市地面格局,减缓城市洪涝灾害损失提供科学参考。

湄公河三角洲洪水特性及其演变规律分析

湄公河三角洲洪涝问题一直是国际社会关注的热点,其洪水特性的不明晰成为制约该地区洪涝灾害治理的短板。基于湄公河三角洲代表站桔井站实测长系列水文资料,采用滑动t检验、Morlet小波变换分析及洪水丰平枯水年划分等方法研究其洪水特性及演变规律。研究结果表明:①湄公河三角洲主汛期平均起止时间为6月30日至11月2日,近年来主汛期历时易发生极端情况,尤以长汛期洪水更为显著;②湄公河三角洲峰现时间集中发生于8~9月,一场洪水历时平均约90 d;③湄公河三角洲桔井站峰高量大,最大90 d洪量与洪峰流量序列存在着35~37 a的周期变换规律;④桔井站洪峰-洪量组合变换多样,洪峰、洪量丰枯变化规律除少数年份外基本保持一致。研究成果可为认识湄公河三角洲复合水文规律提供重要科学依据。

甘肃省庆城县极端暴雨下水保措施抵御暴洪灾害的能力

[目的]最大洪峰流量是导致暴洪灾害的决定性因素。研究小流域降水频率、治理程度与洪峰流量、暴洪灾害损失的关联性,为水土保持减灾防灾工作提供科学依据。[方法]采用回归分析、对比分析等方法,对甘肃省庆阳市庆城县蔡家庙、野狐沟两条相邻流域1981—2022年水保措施的调水效益以及降水因子、水保措施对洪峰流量的影响进行分析。[结果](1)小流域水保措施调水效益随治理程度的提高而增加,随降水频率的提高而减少。(2)年最大日降水量对洪峰流量变化具有极显著的正向影响(p<0.01),贡献率系数为0.707;治理程度对洪峰流量呈负影响,贡献率系数为-0.237。(3)30 a一遇洪峰流量(频率为3%)与50 a一遇洪峰流量(频率为2%)灾害损失强度分别达到1.74×10^(5),3.13×10^(6)元/km^(2),后者比前者增长了16.95倍。[结论]影响洪峰流量变化的主要因素是年最大日降水量。水保措施对削减洪峰流量具有显著的影响。流域治理程度越高,削减洪峰流量的效果越明显,减少暴洪灾害经济损失的能力越大。

基于未来降雨的水库实时优化调度研究

为了充分利用未来降雨信息指导水库调度,构建了以最大削峰为目标的水库实时调度模型,提出了一种考虑未来降雨信息的水库优化调度方法,基于水箱模型利用24 h降雨量预报信息预测入库流量并建立每个时段的泄洪指标求解模型。以山美水库防洪调度为例进行研究,与降雨启发信息优化调度方法进行比较,结果表明,此优化调度方法在目标函数上表现更好,与利用洪水预报的优化调度方法效果相近,能较好地解决来水不确定性的问题。

不同暴雨条件下扇形和羽形流域的洪水规律

为了探讨降雨过程时空分布不均匀性对河道径流的影响,以沂河、沭河流域为例,利用瞬时单位线法和马斯京根法计算重现期为10、 20、 50 a的3 d特征暴雨和2019年台风“利奇马”暴雨在2个流域中的洪水流量,得出各防洪控制站在不同暴雨条件下的洪水规律。结果表明:扇形流域内洪水汇流较集中,容易发生洪灾;羽形流域内各支流洪水交错汇入干流,近水先去,远水后去,洪水较缓和,沂河的防汛压力大于沭河的防汛压力;在相同降雨量条件下,沂沭河流域内临沂站在从北向南的降雨过程中更易形成大洪峰,斜午站、石拉渊站和重沟站在从南向北的降雨过程中更易形成大洪峰;莒县站位于沭河上游,控制流域包含多个支流和3个水库,流域形状为属于羽形流域的沭河流域中的扇形流域,具有洪水汇流集中的特点,沭河莒县站的防汛压力大于沭河其他防洪控制站的防汛压力,而且当沭河流域出现大范围同步降雨过程时,莒县站更易形成大洪峰。