Urban Drainage Area Research Articles

Estimation of sediments in urban drainage areas and relation analysis between sediments and inundation risk using GIS

Sediments entering the sewer in urban areas reduce the conveyance in sewer pipes, which increases inundation risk. To estimate sediment yields, individual landuse areas in each sub-basin should be obtained. However, because of the complex nature of an urban area, this is almost impossible to obtain manually. Thus, a methodology to obtain individual landuse areas for each sub-basin has been suggested for estimating sediment yields. Using GIS, an urban area is divided into sub-basins with respect to the sewer layout, with the area of individual landuse estimated for each sub-basin. The sediment yield per unit area for each sub-basin is then calculated. The suggested method was applied to the GunJa basin in Seoul. For a relation analysis between sediments and inundation risk, sub-basins were ordered by the sediment yields per unit area and compared with historical inundation areas. From this analysis, sub-basins with higher order were found to match the historical inundation areas.

유역형상을 고려한 도시 단위 소유역의 유출 해석

도시 배수구역의 유출특성을 해석하기 위하여서는 유역의 지형특성 및 유출경로를 고려하여 소유역을 분할하고 배수계통에 대한 유출량을 분석하게 되며, 이 과정에서 각 소유역의 도달시간과 시간-면적곡선은 유역형상에 따라 상이하게 구성되므로, 이로 인한 유출특성 또한 크게 변화하게 된다. SWMM 및 ILLUDAS 모형에서는 유역형상을 단순 직사각형으로 가정하여 해석함으로써 유역의 기하학적 형상이 지표면 유출에 미치는 영향을 충분히 반영하지 못하는 한계를 개선하기 위하여, 국토해양부의 FFC2Q 모형 개발연구에서는 유역형상을 고려하여 지표면 유출해석을 실시함으로써 유출분석의 정확도를 향상시키는 기법을 도입하였다. 즉, 지표면 유출해석을 위한 시간-면적곡선법의 적용에서 단위 소유역의 형상을 대칭형(사각형, 타원형, 마름모꼴), 분산형(삼각형, 사다리꼴), 집중형(역삼각형, 역사다리꼴) 형태로 각각 유형화하여 지표면 유출해석을 하였으며, 그 결과를 비교 분석한 결과 유역의 형상에 따라 유출특성이 크게 상이함을 알 수 있었다. 실제로 배수구역(군자 배수구역)에 적용한 결과 유역형상을 직사각형 보다는 마름모꼴로 적용한 경우에 첨두유출량과 유출수문곡선의 형태에서 실측치에 보다 접근하고 있음을 보여 줌으로 써 개선된 결과를 제시하였다. 또한, 유역형상을 고려한 경우에는 첨두유출량의 경우 분할 수에 큰 영향이 없이 실측치와 유사한 안정된 값을 나타내고 있으나, 사각형으로 단순화한 경우에서는 유역 분할 수가 계산 결과치에 민감한 영향을 주었다. In order to describe runoff characteristics of urban drainage area, outflow from subbasins divided by considering topography and flow path, is analyzed through stormwater system. In doing so, concentration time and time-area curve change significantly according to basin shape, and runoff characteristics are changed greatly by these attributes. Therefore, in this development study of FFC2Q model by MLTM, we aim to improve the accuracy in analyzing runoff by adding a module that considers basin shape, giving it an advantage over popular urban hydrology models, such as SWMM and ILLUDAS, that can not account for geometric shape of a basin due to their assumptions of unit subbasin as having a simple rectangular form. For subbasin shapes, symmetry types (rectangular, ellipse, lozenge), divergent types (triangle, trapezoid), and convergent types (inverted triangle, inverted trapezoid) have been analyzed in application of time-area curve for surface runoff analysis. As a result, we found that runoff characteristic can be quite different depending on basin shape. For example, when Gunja basin was represented by lozenge shape, the best results for peak flow discharge and overall shape of runoff hydrograph were achieved in comparison to observed data. Additionally, in case of considering subbasin shape, the number of division of drainage basin did not affect peak flow magnitude and gave stable results close to observed data. However, in case of representing the shape of subbasins by traditional rectangular approximation, the division number had sensitive effects on the analysis results.

ILLUDAS and PSRM‐QUAL predictive ability in small urban areas and comparison with other models

AbstractThe PC versions of the Illinois Urban Drainage Area Simulator ILLUDAS (ILUDRAIN) and the Penn State Runoff Quality Model (PSRM‐QUAL) are used to predict hydrographs from four relatively small urban sites (5·97 to 23·57 ha), each having a distinct land use designation (commercial, high density residential, low density residential, and highway), and all located in south Florida. The description of the sites and observed rainfall and runoff data were available from the US Geological Survey (USGS), and have been used in the past to validate their model (DR3M). The two models were calibrated and verified using measured rainfall–runoff data (72 storm events for calibration and 26 different events for verification) and measured hydrological characteristics of the four sites. The methodology and input parameters are presented. Predicted hydrographs from the two models are plotted against observed ones and show good agreement. Model performance is evaluated using the mean normalized error computation and scattergrams of predicted versus observed data. A comparison is also made with the results, using the same data and drainage areas, of the following three methods/models tested in previous studies: the runoff curve number (SCS) method combined with the Santa Barbara urban hydrograph method (SCS‐SBUH); the Environmental Protection Agency (EPA) stormwater management model (SWMM); the USGS Distributed Routing Rainfall–Runoff Model (DR3M). The predictions from all models tested in this study showed good agreement with the observed data, with better predictions generally obtained for the more impervious sites. Copyright © 2007 John Wiley & Sons, Ltd.

Evaluating Urban Stormwater Drainage Using GIS and RS Techniques—A Case Study in Dhaka, Bangladesh

A method is described, integrating Geographical Information System (GIS) functions, remotely sensed images and hydrologic data, to assess the impact of urbanisation on stormwater runoff and drainage. A sample area is selected in the western part of Dhaka City. First, the urbanization trend of Dhaka was assessed, using multitemporal aerial photographs and satellite images. By combining a spaceborne panchromatic image, the digital terrain model (DTM) and reported hydrological data, an assessment was made of the areal extent of the inundations by stormwater runoff within a specific urban drainage area. The DTM was then modified to accommodate expected urbanization trends and conditions. An assessment was then made of the areal spreading and inundation by the floodwaters, illustrating the impacts of future urbanization on urban storm water drainage.

Stochastic generation of spatial rainfall for urban drainage areas

Data from a dense network of rain gauges in the city of Antwerp (Belgium) has been used to study the stochastic structure of spatial rainfall at the small spatial scale of small hydrographic or urban catchments. The derived spatial rainfall model contains two structures: a deterministic structure for the physical description of individual rain cells and cell clusters, and a stochastic structure for the description of the intrinsic randomness in the sequence of different rain events. Such a model forms the basis of the stochastic generation of spatial rainfall for urban catchments. Spatial rainfall generations have many applications: long-term time series of spatial rainfall can be used as input to urban drainage models for the accurate generation of runoff, or to study model-uncertainties and -biases by the simplified use of point rainfall as a model input.

Stormwater and lamella settlers: efficiency and reality

Two settling devices treating rainwater from urban drainage areas and equipped with secondary sludge treatment were monitored over a period exceeding one year. The two devices differ in their design and in the quantity and quality of effluents received. Full analyses over approximately 30 mean samples of the intake and discharge effluents allowed judgment of the mean efficiency of pollution control and the reduction in impact of the storm water. The observed settlement was compared to measurements of settling velocity during several rainfalls. From analyses of the settled or extracted sludge it was possible to characterize the pollutants retained in the sludge. Particular attention was paid to the functioning and operation of the devices.

Stormwater and lamella settlers: Efficiency and reality

Two settling devices treating rainwater from urban drainage areas and equipped with secondary sludge treatment were monitored over a period exceeding one year. The two devices differ in their design and in the quantity and quality of effluents received. Full analyses over approximately 30 mean samples of the intake and discharge effluents allowed judgment of the mean efficiency of pollution control and the reduction in impact of the storm water. The observed settlement was compared to measurements of settling velocity during several rainfalls. From analyses of the settled or extracted sludge it was possible to characterize the pollutants retained in the sludge. Particular attention was paid to the functioning and operation of the devices.

Stochastic generation of spatial rainfall for urban drainage areas

Data from a dense network of rain gauges in the city of Antwerp (Belgium) has been used to study the stochastic structure of spatial rainfall at the small spatial scale of small hydrographic or urban catchments. The derived spatial rainfall model contains two structures: a deterministic structure for the physical description of individual rain cells and cell clusters, and a stochastic structure for the description of the intrinsic randomness in the sequence of different ram events. Such a model forms the basis of the stochastic generation of spatial rainfall for urban catchments. Spatial rainfall generations have many applications: long-term time series of spatial rainfall can be used as input to urban drainage models for the accurate generation of runoff, or to study model-uncertainties and -biases by the simplified use of point rainfall as a model input.

Technical solutions envisaged in managing solids in combined sewer networks

Solids in combined sewer networks represent two important technical questions: - the clogging of man-entry sewers, and - pollution in urban wet weather discharges, whose main vectors are generally suspended solids. In this paper, we shall present first, curative technical solutions which avoid or remove deposits in man-entry sewers. We shall discuss the partial extraction of the largest solids; selective trapping of bed load solids, which form deposits; and the displacement of deposits using dry weather flow flushing waves. We shall then examine technical solutions to control pollution in urban wet weather discharges. This will show that decantation is an efficient means of fighting pollution. However, it is not always feasible because it involves large scale investments. Complementary methods should, therefore, be developed and used at different points in the water's passage through an urban drainage area.

都市開発における水循環再生システムの総合化に関する研究

Natural rainwater-recirculation has been damaged irresistibly through application of conventional urban drainage systems.If on-site infiltration /storage facilities could be collectively introduced for urban drainage areas, the recirculation is to be likely rehabilitated. For the task, public-private partnership (PPP) should be established, since introduction of the on-site facilities is firstly dependent on cooperation of private secters.The author herein proposes that intermediate system aided by Housing and Urban Development Corporation (HUDC) is effective and/or necessary for promotion of such scheme in the following of widely-applied run-off control measures by HUDC for urbanized river basins, conceptually which is contributed by private sectors.

Adaptation of ILLUDAS for Continuous Simulation

A description is presented of the essential elements of a modified version of the Illinois Urban Drainage Area Simulator model which is used for continuous simulation. The significant changes include a daily soil moisture and initial abstraction accounting scheme coupled with the Horton infiltration model, which is used for runoff simulation of specified events. In addition, three hydrograph routing techniques are incorporated. A screening procedure is described which eliminates from simulation those events which have a low probability of being important in the analysis. An example is presented showing the calibration of a specific catchment and applying 25 yr of continuous rainfall data to obtain a simulated history of peak flows. A frequency analysis of these peaks is then performed as the final goal of the example.

Problems and possibilities in urban drainage

Urban drainage problems in Canada will grow with increasing urbanization. In developing areas problems are related to increased volumes and rates of surface runoff; problems in developed areas are overloaded sewerage systems, combined sewer overflows, and urban surface water pollution. Research and demonstration programs in Canada and the United States are examining potential solutions to these problems. Rate and volume of storm water may be controlled by diversion of unwanted water or by storage. Controls on quantity include source controls, combined sewerage system modifications and operational changes, and treatment methods. Urban drainage models can simulate system behaviour and evaluate performance of alternative solutions. The three most generally useful models are STORM, Storm Water Management Model (SWMM), and the Illinois Urban Drainage Area Simulator (ILLUDAS). Development and application of models may be the most significant single result of urban drainage research and demonstration activities.

Distribution and biomagnification of hexachlorophene in urban drainage areas.

Distribution and biomagnification of hexachlorophene in urban drainage areas.

DEVELOPMENT OF DESIGN STORM HYETOGRAPHS FOR CINCINNATI, OHIO1

ABSTRACT A synthetic storm rainfall hyetograph for a one‐year design frequency is derived from the one‐year intensity‐duration curve developed for Cincinnati, Ohio. Detailed rainfall data for a three‐year period were collected from three raingages triangulating the Bloody Run Sewer Watershed, an urban drainage areas of 2380 acres'in Cincinnati, Ohio. The advancement of the synthetic storm pattern is obtained from an analysis of the antecedent precipitation immediately preceding the maximum period of three selected durations. Rains which produced excessive runoff at least for some duration were considered only. The same approach can be used for other design frequencies. The purpose of this study is to provide synthetic storm hyetographs to be used as input in deterministic mathematical models simulating urban storm water runoff for the design, analysis and possible surcharge prediction of sewer systems.

Where is Urban Hydrology Practice Today?

The evolution of urban street construction and its effects upon urban drainage is traced. Rational method development and inconsistencies in its application are summarized. The emphasis is on lack of absolute precipitation data with resultant inhibiting effects upon development of improved runoff prediction methods. Need for two drainage systems on each urban drainage area is defined. It indicates dual system dividends are reduced drainage costs, reduced flooding losses, and the opportunity to enhance property values, stabilize neighborhoods, and improve urban life quality. Some basic methods for managing urban runoff are also indicated to attenuate peak flows. A low maintenance channel is identified as being more realistic than usual urban channel designs. It points out that direct losses from and expenditures for urban drainage approximate four billion dollars per year. The nation could realize disproportionately great returns from urban hydrology research. The big question is, Does the nation consider it necessary?

Experimental Examination of the Rational Method

Rainfall and runoff data collected in Baltimore, Maryland, from 20 gaged urban drainage areas ranging in size up to 150 acres have been used in a study of the Rational Method. The results suggest it may be nearly correct to assume that the frequency of occurrence of the computed design peak runoff is the same as the frequency of occurrence of the rainfall intensity selected by the designer if an appropriate C value has been selected. Presently used values of C are not adequately based on measurements of rainfall and runoff in urban areas, so large errors can occur when the Rational Method is used. In accordance with their usual design procedures, five storm drainage designers used the Rational Method to estimate 5 yr design peak runoff rates for six gaged drainage areas. These values are compared with runoff values from runoff frequency curves for these gaged areas.

The hydrology of small impervious areas

The rainfall‐runoff relationships on several impervious urban drainage areas varying in size from about 0.4 to 1.0 acre were investigated. The effective storm pattern, divided into a sequence of 1‐minute inputs, provided the basis for generation of a corresponding sequence of runoff outputs, which were combined to produce the total runoff hydrograph. The basic output is a unit hydrograph resulting from an effective rainfall input of 1 minute's duration. (Key words: Runoff; unit hydrographs; urban areas)