Performance Of Drainage Systems Research Articles

Selection of regional historical rainfall time series as input to urban drainage simulations at ungauged locations

It has become established practice during the past 20 years to use high-resolution historical rainfall time series as input to hydrological model packages for detailed simulation of urban drainage systems. However, sufficiently long rain series are rarely available from the exact catchment in question and simulations are hence often based on available rain series from other locations. Extreme rainfall properties of importance to the performance of urban storm drainage systems vary significantly even in regions with only minor physiographic differences. Part of this variation can be explained by regional variations of the mean annual rainfall and the remaining statistical residue can be interpreted as statistical uncertainty. In Denmark, more than 75 high-resolution rain gauges are installed across a total area of 43,000 m. About 40 gauges had sufficiently long records to be included in a comprehensive national investigation where newly developed statistical regionalisation procedures were used to model the regional variation of extreme rainfalls. On this basis, a spreadsheet model was made available for estimation of extreme design rainfalls and the associated uncertainty at any location in the country. Statistics were furthermore computed to classify historical rainfall time series according to the developed regional model, and this makes it possible to assess the uncertainty related with using different historical rain series for simulations at ungauged locations. This research indicates that use of historical point rainfall data at ungauged locations introduces a significant uncertainty that is largely overlooked in today's practice. The engineering recommendation is to select historical rain series based on an evaluation of the local physiographic characteristics (e.g., the mean annual rainfall) and a (pre-defined) desired safety level of the simulations.

Analysis of storage facilities for urban stormwater quantity control

Storage facilities for urban drainage systems are frequently planned and implemented to mitigate the negative impacts of stormwater discharges on receiving waters. For screening level analysis of various runoff control alternatives, cost-effective planning and design of the storage facilities could significantly benefit from analytical tools with explicit solutions to the determination of the relative magnitudes of the storage capacity and the controlled outflow capacity in conjunction with the desired level of system performance. This paper presents methodologies for the development of closed-form mathematical expressions of system performance measures, with which existing drainage system performance and a wider range of alternative designs can be evaluated. As an alternative to continuous simulation for urban stormwater runoff control analysis at the planning stage, these analytical models for stormwater control analysis are developed with the derived probability distribution approach whereby the probability density functions (PDFs) of rainfall characteristics of the catchment are mathematically transformed by rainfall–runoff transformation to create the PDFs of system outputs, such as spill volumes from the storage facility, runoff capture efficiency, etc. This study demonstrates that analytical models, with consideration of the entire spectrum of meteorological conditions, are capable of providing comparable results to continuous simulation models and can be employed as effective tools in urban stormwater management planning.

Investigation and numerical modelling of roof drainage systems under extreme events

In April 2003 the UK Engineering and Physical Sciences Research Council (EPSRC) and a diverse group of interested parties began funding a number of major projects looking at the impacts of climate change on the built environment, transport and utilities. One of these projects, entitled AUDACIOUS, is concerned with the impact of climate change on all aspects of urban drainage systems. The main objective of this project is to investigate key aspects of the effects of climate change on existing drainage in urban areas, and hence provide tools for drainage managers and operators to adapt to uncertain future scenarios. A major element of this work is the development of a set of numerical models to simulate the performance of urban drainage systems under the type of extreme rainfall events associated with climate change. Once developed, it is intended to utilise such models in a diagnostic design capacity, to assist in the formulation of strategies to improve the performance of new and existing urban drainage systems under different climate change scenarios. This paper details the work that has been undertaken at Heriot-Watt University as part of the AUDACIOUS project. To date, this has involved the development of a numerical model to simulate the performance of roof drainage systems (both conventional and siphonic) under extreme rainfall events. The necessary experimental work is described, and the development of the model is detailed. Comparisons between model output and laboratory data are illustrated. Finally, conclusions are drawn regarding the progress to date, and plans for the next stage of the project are outlined.

Operational performance of siphonic roof drainage systems

Siphonic roof drainage systems have been in existence for approximately 30 years, and are becoming an increasingly common element of urban drainage infrastructure. In that time, only limited data have been published relating to their performance, and what does exist relates to laboratory test facilities. This text focuses on the analysis of a large data set obtained from installed siphonic roof drainage systems. Particular attention is given to the ability of the studied systems to prime and meet self-cleansing criteria during sub-design criteria events with return periods of less than one year. Conclusions are drawn regarding the performance characteristics of multi-outlet siphonic roof drainage systems, and plans for future work are outlined.

A-48 実在超高層集合住宅における特殊継手排水システムの能力試験に関する研究 : 地上43階建て超高層集合住宅での現場能力試験の検討

A-48 実在超高層集合住宅における特殊継手排水システムの能力試験に関する研究 : 地上43階建て超高層集合住宅での現場能力試験の検討

Accounting for sensor calibration, concentration heterogeneity, measurement and sampling uncertainties in monitoring urban drainage systems

Assessing the functioning and the performance of urban drainage systems on both rainfall event and yearly time scales is usually based on online measurements of flow rates and on samples of influent and effluent for some rainfall events per year. In order to draw pertinent scientific and operational conclusions from the measurement results, it is absolutely necessary to use appropriate methods and techniques in order to i) calibrate sensors and analytical methods, ii) validate raw data, iii) evaluate measurement uncertainties, iv) evaluate the number of rainfall events to sample per year in order to determine performance indicator with a given uncertainty. Based on previous work, the paper gives a synthetic review of required methods and techniques, and illustrates their application to storage and settling tanks. Experiments show that, despite controlled and careful experimental conditions, relative uncertainties are about 20% for flow rates in sewer pipes, 6-10% for volumes, 25-35% for TSS concentrations and loads, and 18-276% for TSS removal rates. In order to evaluate the annual pollutant interception efficiency of storage and settling tanks with a given uncertainty, efforts should first be devoted to decrease the sampling uncertainty by increasing the number of sampled events.

Irrigation and drainage systems research and development in the 21st century

AbstractOne critical problem confronting mankind today is how to manage the intensifying competition for water between expanding urban centres, traditional agricultural activities and in‐stream water uses dictated by environmental concerns. In the agricultural sector, the dwindling number of economically attractive sites for large‐scale irrigation and drainage projects limits the prospects of increasing the gross cultivated area. Therefore, the required increase in agricultural production will necessarily rely largely on a more accurate estimation of crop water requirements on the one hand, and on major improvements in the construction, operation, management and performance of existing irrigation and drainage systems, on the other. The failings of present systems and the inability to sustainably exploit surface and groundwater resources can be attributed essentially to poor planning, design, system management and development. This is partly due to the inability of engineers, planners and managers to adequately quantify the effects of irrigation and drainage projects on water resources and to use these effects as guidelines for improving technology, design and management.To take full advantage of investments in agriculture, a major effort is required to modernize irrigation and drainage systems and to further develop appropriate management strategies compatible with the financial and socio‐economic trends, and the environment. This calls for a holistic approach to irrigation and drainage management and monitoring so as to increase food production, conserve water, prevent soil salinization and waterlogging, and to protect the environment. All this requires, among others, enhanced research and a variety of tools such as water control and regulation equipment, remote sensing, geographic information systems, decision support systems and models, as well as field survey and evaluation techniques. To tackle this challenge, we need to focus on the following issues: affordability with respect to the application of new technologies; procedures for integrated planning and management of irrigation and drainage systems; analysis to identify causes and effects constraining irrigation and drainage system performance; evapotranspiration and related calculation methods; estimation of crop water requirements; technologies for the design, construction and modernization of irrigation and drainage systems; strategies to improve irrigation and drainage system efficiency; environmental impacts of irrigation and drainage and measures for creating and maintaining sustainability; institutional strengthening, proper financial assessment, capacity building, training and education. Copyright © 2002 John Wiley & Sons, Ltd.

Assessing the performance of urban drainage systems: `general approach' applied to the city of Rotterdam

The Department of Public Works for the city of Rotterdam manages a complex urban drainage system. The system consists of 30 catchments, collects wastewater discharged by 30 pumping stations, to a total of five treatment plants (1.1 million equivalent population). At present control of all these pumping stations is being centralised. To assess the benefits of central control, a performance index (PI) was developed to classify the actual performance of the system under control, during dry weather conditions and during storm events. The PI is composed of deterministic and heuristic indicators that reflect the quality of the control with respect to different objectives set for the entire water system.In a case study the PI was computed for several historic events and showed encouraging results in different modes of control for both dry weather and storm conditions. From the results it can be concluded that the technology described in this paper can help to identify points that need performance improvement in the urban water system in general and in the way it is controlled specifically.

Evaluating drainage design parameters for the fourth drainage project, Pakistan by using SWAP model: part I - calibration.

A transient drainage simulation model,SWAP, was used to evaluate the performanceof drainage systems in (semi-) arid zones.Before application, the model wascalibrated by using 14-months datacollected from two sample fields of theFourth Drainage Project (FDP), Punjab,Pakistan. During the calibration process,emphasis was given to the accuratedetermination of soil hydraulic parameters,reference evapotranspiration, drainage fromsample fields and bottom boundarycondition. Laboratory determined soilhydraulic parameters were foundnon-representative of the field conditions.Difference between laboratory and fielddetermined soil water retention curves werefound significant. The pressure heads andsoil water contents measured in depthincrements of 15 cm were in good agreementwith the simulated values after applying afield measured retention curve. A closeproximity was also found between measuredand simulated average root zone salinity at0–1.0 m depth. The referenceevapotranspiration calculated by thePriestly-Taylor (PT-ET o) methodwas found physically more realistic thanthe Penman-Monteith (PM-ET o)method due to ignorance of the feed backmechanism of vapor pressure deficit onstomatal closure. The simulated cumulativedrainage from two sample fields wascomparable with the calculated values. Theanalysis of piezometer data shows thatthere is a negligible water exchangebetween the deep aquifer and theunsaturated zone. Therefore for scenarioanalysis, no flow conditions at the bottomof the soil profile can be applied as abottom boundary.

Technical brief no. 57: Surface water drainage - How evaluation can improve performance

This technical brief outlines ways in which, by carrying out a simple evaluation, engineers and technicians can make improvements in the performance of drainage systems. Urban drainage is the removal of unwanted water from cities and large towns. When it rains, part of the rainwater, called runoff, runs off the surface and flows along the ground. Surface-water drainage removes this runoff.

LINKFLOW, A WATER FLOW COMPUTER MODEL FOR WATER TABLE MANAGEMENT: PART 2. MODEL VERIFICATION

A computer simulation model, LINKFLOW, was developed to compute the movement of water during various water table management practices. The development of the model and validation with field data has been covered in related articles (Havard et al., 1995a,b). This article describes the use of the model to investigate the effects of anisotropy and clay lenses on water table elevations during water table management. The first application considers subirrigation and drainage in an anisotropic soil, and the second describes effect of clay lenses on subirrigation and drainage system performance. The results of simulations suggest that water table management system performance can be significantly affected by soil anisotropy. Case simulations for subirrigation and drainage showed 18% and 25% reductions in water movement into and out of the drains respectively when the anisotropy of the soil increased from one to five. Further simulations showed the effect of clay lenses in the soil profile and how backfilling during installation would benefit subirrigation and drainage system performance. Backfilling around the drains for a soil with low permeability lenses showed 70% increase in water flow after 21 days of subirrigation.

LINKFLOW, A WATER FLOW COMPUTER MODEL FOR WATER TABLE MANAGEMENT: PART 3. MODEL APPLICATION

A computer simulation model, LINKFLOW, was developed to compute the movement of water during variouswater table management practices. The development of the model and validation with field data has been covered inrelated articles (Havard et al., 1995a,b). This article describes the use of the model to investigate the effects of anisotropyand clay lenses on water table elevations during water table management. The first application considers subirrigationand drainage in an anisotropic soil, and the second describes effect of clay lenses on subirrigation and drainage systemperformance. The results of simulations suggest that water table management system performance can be significantlyaffected by soil anisotropy. Case simulations for subirrigation and drainage showed 18% and 25% reductions in watermovement into and out of the drains respectively when the anisotropy of the soil increased from one to five. Furthersimulations showed the effect of clay lenses in the soil profile and how backfilling during installation would benefitsubirrigation and drainage system performance. Backfilling around the drains for a soil with low permeability lensesshowed 70% increase in water flow after 21 days of subirrigation.

Modeling Time-Dependent Behavior of Pavement Drainage Using Linear System Identification and Neural Network Techniques

Inadequate drainage continues to be a major cause of problems associated with long-term structural integrity and performance of roadway pavements. To reduce the impact of these drainage-related problems, it is customary to provide measures to prevent water from entering the pavement system and to enhance the drainage capability of the pavement base to rapidly move the water that inevitably finds its way into the pavement system. The performance of different drainage systems in the field is not clearly known. Oklahoma Department of Transportation (ODOT) has been collecting rainfall and outflow information at sites with edge drains since 1992. The sites have different types of surfaces, base courses, and edge drains. The data collected by ODOT at these sites were used to develop two types of numerical models to predict the outflow–time history using rainfall–time history as the input. One model is based on linear system identification theory, and the other model is based on an artificial neural network. The development of these models is presented, and the model predictions are compared with the measured field data. The efficiency of the drainage systems, including the AASHTO criteria for the drainage time, at these sites is compared by using the numerical models and synthetic, but the same, rainfall events.

Reappraisal of flow to tile drains III. Drains with limited flow capacity

This third paper of the series on the reappraisal of flow to tile drains considers the time-variant situations in tile drain drainage systems when the quantity of water carried by tile drains is limited due to the capacity of the drains or the pumping equipment. Two categories of problem are analysed in this paper: (i) a series of parallel tile drains with a maximum specified flow and (ii) interceptor drains in the vicinity of canals. Complete details for satisfying the maximum specified flow conditions in tile drains are given. The effect of different capacities of tile drains on the performance of drainage system is explored.

Irrigation-Drainage Design and Management Model: Validation and Application

The Colorado State University Irrigation and Drainage (CSUID) model is a simulation model, which can be used in the design and management of conjunctive irrigation and drainage systems. It is based on the numerical implementation of a quasi-three-dimensional finite-difference model, which solves the Richards equation and the advective-dispersive transport equation for one-dimensional vertical flow and salt transport in the variably saturated zone above the water table; and it also solves the depth-averaged Boussinesq equation and two-dimensional advective-dispersive transport equation for areal flow and transport in the fully saturated zone below the water table. In the paper, the model is validated and applied. Its performance is compared to known analytical solutions of simplified problems, the performance of other numerical models, and results of reported laboratory and field experiments. Its capabilities as a design and management tool are demonstrated by considering a hypothetical field problem. It is shown that the model can be used to evaluate design and management strategies to achieve the improved performance of conjunctive irrigation and drainage systems.

Review of Transport Research Laboratory research on highway drainage

Abstract Drainage measures are an important means of ensuring the stability of highways and associated structures. Much of the TRL research on highway drainage has been directed towards examining the field performance of drainage systems, usually over extended periods. This paper describes studies mainly by TRL on edge of pavement drainage, slope drainage, drainage to retaining structures, and drainage blankets. The results are described in relation to current UK practice.

Technical Notes: A Comparison of Two Saturated Hydraulic Conductivity Measuring Techniques in Relation to Drain Installation Methods

Saturated hydraulic conductivity (Ks) is an important parameter influencing subsurface drainage design and performance, and Ks can be affected by subsurface drain installation methods. Ks was measured at a field site at Nashua, Iowa, with 1.2-m (4-ft) deep drain lines installed with a trenchless plow and with a chain trencher at four depths [0 to 150, 150 to 450, 450 to 750, 750 to 1000 mm (0 to 6, 6 to 18, 18 to 30, 30 to 40 in.)] using the Guelph permeameter (in situ technique) and the constant head permeameter method (laboratory technique) on undisturbed soil cores which were removed from the field site. Ks values were 10 to 130 times greater for the constant head permeameter compared to the Guelph permeameter method and were significantly different at all depths for the two measurement methods. The laboratory technique yielded greater standard deviation values for all depths, whereas the coefficient of variation values were greater for the in situ technique. Drain line installation methods did not significantly affect Ks at the 0 to 150 and 150 to 450 mm (0 to 6 and 6 to 18 in.) depths; however, at the 450 to 750 and 750 to 1000 mm (18 to 30 and 30 to 40 in.) depths, the trencher installation method had Ks values two to three times greater than the trenchless installation method and these differences were significantly different. Subsurface drain line installation method can affect the Ks values particularly near the drain line depths; however, these affects did not affect drainage system performance 10 years after installation.

Comparison of Subsurface Drainage Theories for Drainage of Waterlogged Saline Soils of Haryana State, India

A field experiment was conducted to study the performance of subsurface drainage systems in the waterlogged saline soils of Central Haryana, India. Some steady state and non-steady state subsurface drainage equations were compared with measured field data to test their applicability in the area. A drainage rate equal to a drop in water table of 30 cm (11.8 in.) in two days from an initial mid-point water table reaching the ground surface is satisfactory for common drainage sensitive crops on salt affected lands. A drain spacing of 48 m (157 ft) placed at a depth of 1.75 m (5.7 ft) is recommended for the drainage of waterlogged saline soils of Central Haryana, India.

Hydraulic Capacity of Control Devices for Water Table Management Systems

In the design of water table management systems, the hydraulic capacity of the drain tubes and the outlet are usually assumed to be adequate to carry drainage and runoff from the fields and, thus, outlet limitations are not addressed. Unfortunately, some of the devices developed for closed control systems may sacrifice a portion of the outflow pipe area in the control mechanism and restrict the outflow rate. Three commercial outflow control devices were evaluated for outflow rate and were compared to a hypothetical flashboard riser system. Each of the devices restricts the flow by about 70% as compared to the flashboard riser when the head is about 0.15 m (0.5 ft). However, at an area of about 0.45 ha (1.11 ac), the flow capacity of the 15 cm (6 in.) tubing will begin to limit the mainline outflow rates for the site and system conditions in the analysis. With proper design, currently-available, commercial flow-control devices will be of sufficient capacity and will not be a limiting factor in determining drainage system performance.

Cultivation and drainage performance on former opencast coal mining land

Abstract. The effect of various cultivation sequences on the performance of field drainage systems was investigated in a number of case studies carried out on former opencast coal mining land. Comparisons of drain flow patterns before and after cultivation indicated marked deteriorations in performance following preparation of the final seedbed. Neither mouldboard ploughing nor discing alone affected drain flow.Soil moisture, hydraulic conductivity and drain flow data suggested that drainage performance may have deteriorated as a result, initially, of secondary drainage channels being blocked with fine materials translocated from the seedbed. A subsequent collapse of tilth to form a surface pan reinforced this adverse effect. It was not clear to what extent the failure of secondary drainage channels contributed to this collapse.Implications for the management of former opencast land and the advantages of various cultivation techniques are discussed.