Drainage Design Research Articles

Drainmod-Linked Interface for Evaluating Drainage System Response to Climate Scenarios

Abstract.This article presents the development of a drainage-climate interface that incorporates climatological data, crop drainage requirements, and drainage theory into a procedure for characterizing drainage system response under different climate scenarios. The drainage-climate interface is suitable for assessing potential county-level impacts of climate change on crop production, soil hydrology and subsequently on subsurface drainage design. Climate model projections from two general circulation models (GCMs), namely CCSM4 (Community Climate System Model) and MIROC5 (Model for Interdisciplinary Research on Climate), were used to create the climatological database for the drainage-climate interface. DRAINMOD was integrated into the Visual Basic for Applications (VBA) portion of the interface to simulate the performance of subsurface drainage systems in Illinois for the near future (2040 to 2069) and the far future (2070 to 2099) periods. Case studies were developed with the interface for Adams and Champaign Counties in Illinois for their predominant soil types. Hydrologic simulations from the interface were used to determine the optimal depth and spacing of tile drains that maximize crop yield for corn and soybean during the mid and late 21st century. Drainage water management (DWM) was incorporated into the drainage-climate interface to investigate the potential of DWM in the future climate scenarios to maintain water quality, reduce nutrient losses and minimize pollutant loading from drained fields by controlling the timing and amount of water discharged from agricultural drainage systems. Results from DRAINMOD simulations with MIROC5 show a significant decline in crop yield due to extreme heat stress. Corn yield in the future showed a severe reduction while the yield for soybean demonstrated a gradual decline over the years. DWM had only a minimal effect on future crop yield trends. The drainage-climate interface simulated subsurface drainage conditions and made evident the consequences of environmental conditions on crop physiological processes under scenarios of climate change predicted by MIROC5. Keywords: Agricultural system models, Climate change impacts, Drainage-climate interface, Drainage water management, Subsurface drainage, Tile drain depth, Tile drain spacing.

Evaluating Effect of Subsurface Drain Spacing and Depth on Hydrological Properties of Waterlogged Vertisols in Sangli, Maharashtra

A field experiment was conducted to evaluate the effect of subsurface drain spacing and depth on hydrological properties of waterlogged Vertisols under sugarcane in Sangli district of Maharashtra during 2012-13 to 2013-14. A total of 12 treatments consisting four drain spacings of 10, 20, 30 and 40 m and three drain depths of 0.75, 1.0 and 1.25 m were laid in experimental plot. The saturated hydraulic conductivity of soil was determined before and after harvesting of sugarcane. Drainable porosity of soil corresponding to water table depth was determined from water table drawdown and drain discharge measurements after rainfall. It was found that the closely-spaced and deep drain recorded better hydrological properties of soil (drainage coefficient, water table depth, saturated hydraulic conductivity, and drainable porosity) as compared to widely-spaced and deep drains. But closely-spaced drains increased the initial adoption cost of subsurface drainage system, drained excess water, and leached more nutrients. Drain spacing and depth of either 40 m and 1-1.25 m, or 30 m and 1 m confirmed the recommended basic guidelines for Indian subsurface drainage design with optimum drainage coefficient of 2 mm.day-1 for semi-arid regions and drain spacing between 30-50 m and 1.2 m depth for fine-textured soils.

Hubungan Antara Elevasi Muka Air Waduk Dan Panjang Lintasan Rembesan Terhadap Debit Rembesan Pada Bendungan Urugan Batu Inti Tegak (Studi Kasus Bendungan Jatibarang)

Rockfill dams have better stability than homogeneous soil dams. It allows to design the dam more slim with a higher slope. The disadvantage of rockfill dam is in the core zone as an impermeable zone. Zoned vertical core rockfill dam is a combination of various material properties. Geometry and drainage design will affect the seepage and phreatic line properties that occur. Numerical modeling and calculations are used to calculate the seepage profile more accurately. The combination of the parameters of the permeability coefficient (K), reservoir water level (Δh) and the length of the seepage path (L) can be used to determine the relationship between parameters with the same unit. 2D modeling take into account saturated/unsaturated conditions with steady state on each parameter. This study uses the Jatibarang-Indonesia dam as a basic model. The seepage profile at condition K1 (k = 1x10-5cm/sec) is q/k = -0.0018 (h2/L)2 + 1.3496h2/L + 53.241 and the seepage profile K2 (k=1x10-7cm/s) is q/k = -0.1521 (h2/L)2 + 90.402h2/L + 5480.2. This equations can be used to estimate seepage that occurs in a dam of other rock fill zoned vertical core dam based on the permeability coefficient value (K) more practically for all values of Δh and L reviewed.Keywords: Seepage, Rockfill Dam, Permeability, FEM, Numerical Analysis

RESULTS OF FIELD OBSERVATIONS OF ENGINEERING DRAINAGE EFFICIENCY

Relevance of research. Engineering drainage is an important element of the system of territory protection against the harmful water effects, which enables to carry out agro-industrial production, ensure safety for population, prevents floods and salinization development etc. Considerable restoration of irrigation and drainage, which is planned to be carried out in the southern regions, requires more research in the experimental and production areas. The results of field studies will be widely used in the design of drainage, justification of its schemes, types and parameters.
 Purpose of research is to study the results of field observations of engineering drainage on the irrigated agriculture area for their further use in design.
 Research methodology and objects. On-site drainage studies were conducted in the pilot production areas (PPAs), which are located on agricultural lands both on major irrigation systems and in settlements. The studies cover the period from 1990 to 2019. The areas with horizontal and vertical drainage were selected for the study.
 Results of the study and main conclusions. Based on the results of the research, it was determined the conditions of the drainage systems functioning, the genesis and the causes of flood development, the mechanism of groundwater depth and the dynamics of ground water table fluctuations in the drainage areas and adjacent territories. It was established the efficiency of drainage in difficult natural and water management conditions on the main irrigation systems and in a number of settlements. It was found that in the conditions of low drained and drainless relief, closed horizontal drainage systems with the laying of the collector drains to a depth of 7.5 m and gravity drainage operated with the highest efficiency. Such drainage systems provided groundwater stabilization at depths of 3-4 m or more due to the operation of deep-laying collectors without the involvement of less deep field drains. The excavation revealed that high efficiency of horizontal drainage was facilitated by the use of geotextile drainage filters, which avoided critical siltation and penetration of root systems into the pipe cavity. The efficiency of vertical drainage was dependent on the mode of its operation and the technical condition of water wells and pumping power equipment. Vertical drainage requires the implementation of additional measures to protect the areas against flooding – laying of horizontal drainage, development of the collector network, use of water wells for collecting surface and drainage water.

DRAINAGE AND LIGHTING SYSTEM DESIGN IN ZODIA PARK, PETUKANGAN UTARA, SOUTH JAKARTA

Zodia Park is one of the city park located in South Jakarta. As a green open space, Zodia Park have some great benefits for community. At now, Zodia Park conditions do not have lighting system that complies with safety standards. The lighting system in this park is still provided by residents independently. Moreover, during heavy rain, the park will be inundated between 20-30 cm. It is because the Zodia Park is located at near inspection river. Thus, in this community service, the team proposes the drainage and lighting system design as a contribution to Forestry Office who maintains the Zodia Park to overcome this problem.

Analytical solutions of non-Darcy seepage of grouted subsea tunnels

Fluid flow in porous media is very important in a wide range of hydraulic and geotechnical engineering fields. The theoretical basis of fluid flow in porous media is based on the Darcy’s law. There are evidences that the fluid flow in porous media does not follow the Darcy’s law at very low velocity. The Darcy’s law is inappropriate for the low-permeability grouting zone of a subsea tunnel. Therefore, in this paper, we propose the impact of nonlinearity of low velocity flows on the drainage design of grouted subsea tunnels. The analytical solutions are derived by complex variable functions based on Hansbo's non-Darcy seepage model. The advantages of considering non-Darcy effects in the design of tunnel drainage system have been proved by both field monitoring and experimental data. The applicable conditions of our analytical solutions in subsea tunnel design and constructions are given. The analytical solutions are verified by numerical simulations and analytical analyses. The influences of non-Darcy parameters on the total hydraulic head and water inflow of grouted subsea tunnels are discussed. The design parameters of the grouted subsea tunnels, such as the ratio of permeability coefficients kr/kg and the grouted zone thickness hc, are investigated considering non-Darcy seepage. The results show that the non-linear seepage parameters have great influences on water inflow and water pressure of subsea tunnels. Our proposed methods can provide references for the drainage design in subsea tunnel projects.

Research on Determination Method of Gas Drainage Radius Based on Elastoplastic Softening Model

Based on the elasto-plastic softening model and the theory of gas seepage, this paper establishes the calculation model of the gas pressure and the pumping time of the coal around the mining. The COMSOL Multiphysics simulation software is used to simulate the gas pressure of the surrounding coal Distribution with time. According to the basic parameters of the 3# coal seam in the mine, the simulation results show that the effective sampling radius is 1.5m and the model is 1.6m, and the error is small within the allowable range. Based on the elastic - plastic softening model, the mining radius can provide the basis for the design of mine coal mining and drainage, improve the efficiency of gas extraction and ensure the safety of mine production.

Design of Flood Drainage in Golgohar Iron Ore Mine#3

The iron ore minerals reservoir of Golgohar Mine#3 is more than 660 million tons. It is the biggest in Iran and rate of ore extraction is more than 15 million tons per year. The pit takes place on the way of runoff pathway of this watershed and it needs an especial strategy for conserving the pit mine during next imminent floods. The area of Mine# 3 watershed is 20785700 square meters and its general slope in its topography map is 0.59 percent; then initial scheming indicates it can causes a great deal of problems for mining operation n the next floods; particularly, the pit is located into degree 4th sub branch of a main ephemeral river. For this purpose, the Soil Conservation Service Curve Number (SCS) method was employed to estimate intervals period of next floods based on the magnitude, the intensity and the duration of precipitation events data. Conceptual design of runoff drainage of the watershed was designed to lead the flood to a better pathway location. The Mine#3 overburden deposition occupies a huge area on the watershed; and it has been considered and redesigned in terms of size, form, dimensions and location to manage as a physical obstacle against next floods. Hydraulic calculations were applied for designing two essential open channels which can preserve the pit.

Comparison between Graded Crushed Gravel Filter and Textile Filter using Statistical Analysis

Many researchers have applied several experiments and research studies by developing criteria's design of drainage to improve the drainage process, and to show that the filters plays an important role to improve and maintain the drainage system from being blocked due to siltation. There are several types of filters, including granular mineral materials and organic materials, the other filter that was used is made from a special fabric material such as paper, burlap, or special fabric textile material. The objective of this study is to evaluate the performance of textile filters, and if it is desirable and suitable for Iraqi soil using statistical analysis. This study was conducted in the laboratory using sand tank model and two types of filters (graded crushed gravel and textile) with two types of soil (sandy soil and loamy soil) to compare and evaluate the hydraulic performance and the efficiency of utilizing textile filter instead of graded crushed gravel filter in drainage systems using statistical analysis methods. These statistical analysis show that there was a good agreement between measured and theoretical values of entrance resistance when using the two filters in sandy soil. On the other hand, the results showed that there was a weak performance when textile filters in were used in heavy soil (loamy soil) due to the high value of root mean square error (RMSE) and low value of agreement index (d). The results of statistical analysis show that the textile filter is desirable and suitable for Iraqi soil especially for sandy soil due to low entrance resistance of flow compared to loamy soil.

Modelling of soil permeability using different data driven algorithms based on physical properties of soil

Soil permeability is an important parameter for assessment of infiltration, runoff, ground water, drainage and structures design. In the current research, five different data driven algorithms namely Multilayer Perceptron (MLP), Co-Active Neuro-Fuzzy Inference System (CANFIS), Support Vector Machine (SVM), Decision Tree (DT) and Random Forest (RF) algorithms and also, their wavelets (W-MLP, W-CANFIS, W-SVM, W-DT and W-RF algorithms) were used to predict soil permeability based on physical properties of soil. Also, reliable information/input vectors were assessed based on Gamma Test (GT). Sand, silt, clay and organic content (OC) parameters were chosen as information vectors based on gamma test. The potential of data driven algorithms were evaluated based on different statistical indices during model development and validation phase. It was found that wavelet based algorithms viz. W-MLP, W-CANFIS, W-SVM, W-DT and W-RF simulated better results of soil permeability compared to non-wavelet (MLP, CANFIS, SVM, DT and RF) algorithms. Among all wavelet and non-wavelet algorithms, W-RF algorithm had the highest accuracy and efficiency of model. The results of sensitivity analysis indicated that clay > silt > sand > OC > BD > PD was the order of sensitive parameters for soil permeability prediction based on data driven algorithms.

Effect of underdrain design, media height and filtration velocity on the performance of microirrigation sand filters using reclaimed effluents

Sand filters are commonly used in microirrigation systems to prevent emitter clogging, especially when wastewater is used. However, little is known about the operating conditions required to guarantee a good filtration and a low energy consumption. For this reason, three sand filters with different drainage designs (collector arms, inserted domes and porous medium) using reclaimed effluents were analysed when operating with two sand media heights (0.20 and 0.30 m) and two filtration velocities (30 and 60 m h−1). Each one of these four different operating conditions (combination of two sand media heights and filtration velocities) was tested for 250 h. Filtered and backwashed volumes, energy consumption during filtration and backwashing, inlet and outlet filter pressures, and water quality parameters at filter inlet and outlet were recorded using a supervisory control and data acquisition system. Results showed that porous media underdrain design presented higher turbidity removal efficiencies for most of the tested conditions (38.53, 33.63 and 10.51% at 0.20 m/30 m h−1, 0.20 m/60 m h−1 and 0.30 m/60 m h−1, turbidity removal, with sand media height/filtration velocity, respectively) and dome underdrain only at 0.30 m/60 mh−1 (47.74%). Porous media underdrain also filtered more water volume per electrical energy unit (8.30 m3 kWh−1) than domes and arm collector underdrain (8.18 and 8.07 m3 kWh−1, respectively). In general, filtration velocities of 30 m h−1 showed higher turbidity removals and filtered more water volume per electrical energy unit than 60 m h−1. Media height did not show a clear effect, but smaller media heights did allow energy and material saving.

Non-uniform Distributions of Gas Pressure and Coal Permeability in Coalbed Methane Reservoirs Induced by the Loess Plateau Geomorphology: A Case Study in Ordos Basin, China

Coal mine methane (CMM) accumulation and permeability distribution characterization are the bases for a successful CMM drainage design. Before extending degassing activities, the prediction of the gas pressure and permeability distributions of the pre-drainage area is recommended. The effects of CMM geology on gas occurrence and coal permeability have drawn much attention and contributed to numerous research findings. However, the loco-regional distribution characteristics of the gas occurrence and coal permeability induced by landform characteristics have barely been investigated. This paper presents a quantitative case study on the non-uniform distributions of the gas pressure and coal permeability induced by the Loess Plateau geomorphology. Based on the collection and analysis of a large amount of data, the non-uniform distribution of the burial depth was first obtained. The relationship between the burial depth and gas pressure was analyzed by using the safety line method. A series of efforts were made to perform experimental tests for determining the competing influences of the effective stresses and sorption-induced strain on the coal permeability, and the relationship between the burial depth and coal permeability was analyzed by using the modified PM model. Finally, a quantitative evaluation of the non-uniform distributions of the gas pressure and coal permeability induced by the Loess Plateau geomorphology was achieved. The results showed that the statistical burial depth, gas pressure, and permeability of the No. 3 coal seam were irregular with large loco-regional changes, and the range of the burial depth was from 349 to 479 m. Further, the predicted pressure was from 0.81 to 1.66 MPa, and the predicted permeability was from 0.0155 to 0.01968 mD. When using both the gas pressure and coal permeability as the evaluation indices of the difficulty of gas drainage, the study area could be divided into six parts and classified into two groups. The division of a coal seam influenced by the Loess Plateau geomorphology will provide essential information formulation and economical plan to degas it.

Calibration of DRAINMOD for prediction of water table depths and drain discharges under waterlogged Vertisols of Maharashtra, India

An estimation of optimal design parameters of subsurface drainage system through monitoring of water table depths and drain discharges are expensive in terms of time and money. The simulation modeling is an effective tool for estimation of drainage design parameters at less cost and short time. In view to this, calibration of DRAINMOD model for prediction of water table depths and drain discharges were conducted by installing subsurface drainage system with 40 m drain spacing and 1.0 m drain depth at Agricultural Research Station, Kasbe Digraj, Dist. Sangli (Maharashtra) during 2012-13 to 2013-14. The field data on water table depth and drain discharge were used for calibration of DRAINMOD model. The input data files on climatic, soil, crop and drainage design system parameters were attached to DRAINMOD model and calibrated successfully. It is found that both observed and simulated water table depths and drain discharges showed a fluctuating trend and predicted both water table depths and drain discharges closely with the observed values during frequent rainy days and following the rainy days. The DRAINMOD model reliably predicted water table depths with a goodness of fit (R2 = 0.97), MAE (12.23 cm), RMSE (15.49 cm) and CRM (0.05); drain discharges with R2 of 0.93, MAE of 0.095 mm day-1, RMSE of 0.1876 mm day-1and CRM of 0.04. Thus, the calibrated DRAINMOD model can be used to simulate the water table depths and drain discharges in semi-arid climatic conditions of Maharashtra and in turn to estimate and evaluate drain spacing and depth.

ĐỀ XUẤT CÁC GIẢI PHÁP GIẢM THIỂU TÁC ĐỘNG DO ĐỔ THẢI BÙN CÁT NẠO VÉT Ở VÙNG VEN BIỂN HẢI PHÒNG

Located in the estuary region of the Red - Thai Binh river system, in which the estuarine turbidity maxima occur, the deposition of navigation in waterways to Hai Phong ports is always an urgent problem that needs to be solved. At the present time, it is not easy to use dredged sediment for landfilling or other purposes. Moreover, it is also difficult to dispose of them on the land because of requiring the design and construction of dikes, requiring compaction and drainage of dumped materials. Therefore, disposing of materials at dumping sites in Hai Phong open waters is still an alternative for considering. However, the suspended sediment from the dumping sites can cause influences on the marine environment and ecosystems. Based on the characteristics of natural conditions, socio-economy and ecological environment in Hai Phong coastal areas as well as results of the modeling application (Delft3D model), this paper gives some proposals for appropriate solutions to reduce influences of sediment dumping activities in the Hai Phong open waters. They are: (1) Planning a land for reclamation of dumped materials, (2) Research on the strategies to use dredged sediments as a resource, (3) Finding a best method of dumping, (4) Considering tidal current for daily dumping, (5) Choosing disposal time during neap tide, (6) Restricting disposal in case winds come from SW and S, (7) Reducing time and the number of dumping, increasing amount of sediments in each dumping, (8) Applying technologies in disposal monitoring, (9) Regularly monitoring the environment at the dumping sites and adjacent areas.

LID coupled design of drainage model using GIS and SWMM

ABSTRACT Urbanization creates developed catchment and generates peak flows in a short time. Upgradation of the existing drainage system to accommodate those altered flows have become a challenging task. As a result, implementation of LIDs in urban areas, nowadays, becomes a traditional solution to mitigate urban runoff issues. However, the integration of LIDs in urban drainage design still have not yet been fully investigated. In this paper, the LID coupled drainage system is designed for Aurangabad city (Maharashtra State, India) by using SWMM. Design of drainage model has been classified into two groups as a conventional drainage system and a system with low impact development (LID) to investigate the performance of the LID coupled drainage model. The results of the model simulation show that a combination of at least two or more LID implementation is necessary for satisfactory results. The finding of the study shows that RWH is more effective in highly urbanized areas, whereas, pervious pavement gives satisfactory results in moderately urbanized areas. Also, LID practices can effectively reduce the pressure on the urban drainage system if two or more LIDs are coupled together. Therefore, Simulation results suggest implementing a drainage system with the implementation of pervious pavement and RWH. Abbreviations: AMC: Aurangabad Municipal Corporation; BMPs: Best Management Practices; CPHEEO: Central Public Health and Environmental Engineering Organization; GIS: Geographic Information System; IDF: Intensity-Duration-Frequency; IRC: Indian Road Congress; LID: Low Impact Development; LULC: Land Use Land Cover; RWH: Rainwater Harvesting; SWAT: Soil and Water Assessment Tool; SWMM: Storm Water Management Model; US EPA: United States Environmental Protection Agency

Automated rainfall simulator for variable rainfall on urban green areas

AbstractRainfall simulators can enhance our understanding of the hydrologic processes affecting the total runoff to urban drainage systems. This knowledge can be used to improve urban drainage designs. In this study, a rainfall simulator is developed to simulate rainfall on urban green surfaces. The rainfall simulator is controlled by a microcomputer programmed to replicate the temporal variations in rainfall intensity of both historical and synthetic rainfall events with constant rainfall intensity on an area of 1 m2. The performance of the rainfall simulator is tested under laboratory conditions with regard to spatial uniformity of the rainfall, the kinetic energy of the raindrops, and the ability to replicate historical and synthetic rainfall events with temporally varying intensity. The rainfall simulator is applied in the field to evaluate its functionality under field conditions and the influence of wind on simulated rainfall. Finally, a field study is carried out on the relationship between runoff, soil volumetric water content, and surface slope. Performance and field tests show that the simulated rainfall has a uniform spatial distribution, whereas the kinetic energy of the raindrops is slightly higher than that of other comparable rainfall simulators. The rainfall simulator performs best in low wind speed conditions. The simulator performs well in replicating historical and synthetic rainfall events by matching both intensity variations and accumulated rainfall depth. The field study shows good correlation between rainfall, runoff, infiltration, soil water content, and surface slope.

Hydropedological Data Necessary for Computing Drain Spacings in a Gleysol

Gleysols comprise soils saturated with groundwater for long enough periods to develop reducing conditions resulting in gleyic properties. Gleysols occupy more than 720 million ha worldwide, on low positions in landscapes with high groundwater table. Evidence of reduction processes with segregation of Fe compounds starting in the first 40 cm of the soil surface. For many gleysols the main obstacle to utilization is the necessity to install a drainage system to lower the groundwater table. With a particle – size distribution clayey – loamy (44.8-42.9% clay), a great bulk density (1.50-1.57g/cm3), and SAR 12.5, these soils have a poorly natural drainage, from which water is removed very slowly. The volume of all pores, namely porosity, is very small in the second horizon, 38.3%. The primary function of a drainage equation is the computation of drain spacings for drainage design. An analysis reveals the influence of the various factors, as permeability, thickness of the soil layers, depth of drains, discharge rate in surface, effective porosity, drainage intensity etc; namely geohydrological investigations. In order to determine the drain spacing on the Gleysols we have used a similar method with the auger-hole method (1970, van Beers) but with 4 holes. The water was removing from the central auger-hole with a bailer, the time interval was 20 minutes. The analytical data of measurements are in the tables 2 and 3. Knowing the pumped and extracted water volumes from central auger hole which has perforated tube, we have obtained the final values of effective (or drained) porosity (0.0197-0.0208). For the drain space calculation, we recommend to use 0.0208, the finally value.

Opposition to housing development in a suburban US County: Characteristics, origins, and consequences

Local opposition to new housing is a well-known phenomenon, but the degree to which it characterizes planning debates or influences outcomes, relative to more supportive stances, is less understood. This paper investigates public comments recorded at public hearings regarding housing-related rezoning cases in order to quantify the amount of comments that can be characterized as oppositional, as well as the sources and effects of this opposition. We conducted a survey of comments made over three decades by 994 individuals appearing at planning commission hearings concerning 330 rezoning cases in Henrico County, Virginia (USA). We find that the overwhelming majority (85.8%) of individuals expressed negative sentiments, that this negativity was consistent throughout the study period, and that this negativity was most often stated in terms of anxieties over traffic, flooding, road connections and access, proposed development density, and property values. Using logistic regression analysis, we find that larger rezonings, the incorporation of multi-family or zero lot-line housing, higher census tract populations, increases in homeownership, increasing population density, and increasing racial diversity are all significantly associated with higher levels of opposition. Opposition in the case study county contributes to the adoption of numerous zoning conditions related to traffic, drainage, and site design, but more commonly to restrictions on density and increased floor areas.

Vulnerability analysis method of vegetation due to groundwater table drawdown induced by tunnel drainage

Tunnel drainage demonstrates a behavior that constantly drains the high-ground subsurface water that feeds the overlying vegetative cover. The environmental impact of construction process on groundwater table drawdown can be evaluated using groundwater models. However, considering only the effects of drawdown is insufficient to evaluate the vulnerability between the terrain surface and groundwater table. We proposed a vulnerability analysis method based on soil water pressure by including the Soil-Plant-Atmosphere Continuum (SPAC) approach. We defined the vulnerability based on the wilting point of the terrain vegetation. A theoretical case study representing the groundwater level alterations that induce permanent wilting was investigated. The vulnerability analysis method takes account of two important factors; vegetation type and soil textures. The results show that wilting is more infiltration dependent, therefore, it does not occur immediately once the water table is lower than rooting depth. Soil water pressure losses caused by groundwater table drawdowns are compensated when sufficient infiltration occurs. Without sufficient infiltration, soil texture is an important factor for the resilience of vegetation cover under the influence of groundwater table drawdown. In our case study, layered soils lead to a flow behavior which makes the vegetation reach permanent wilting earlier than the homogeneous counterpart. Vulnerability analysis of vegetation cover can be regarded as an important step for an environment-friendly tunnel drainage design.

Uncertainty quantification of flood damage estimation for urban drainage risk management.

This paper presents a method of quantifying the uncertainty associated with inundation damage data for an urban catchment when undertaking stormwater drainage design and management. Usually flood damage is estimated by multiplying the inundated asset value by the damage rate corresponding to the inundation depth. The uncertainty of the asset value and the damage rate is described by probability distributions estimated from an analysis of actual flood damage data from a national government survey. With the inclusion of uncertainty in the damage rate and asset value, the damage potential curve defining the damage-frequency relationship is no longer a deterministic single-value curve. Through Monte Carlo simulations, which incorporate the uncertainty of the inundation damage from the damage rate and asset value, a probabilistic damage potential relation can be established, which can be expressed in terms of a series of curves with different percentile levels. The method is demonstrated through the establishment of probabilistic damage potential curves for a typical urban catchment, the Zenpukuji river basin in Tokyo Metropolis, under two scenarios, namely, with and without a planned flood control reservoir.