P. Sreeja

A methodology for determining runoff based on imperviousness in an ungauged peri-urban catchment

A semi-distributed hydrological model has been developed in this study for determining runoff in an ungauged peri-urban catchment of north east India. In the absence of discharge data, the study has focused on how to improve the accuracy of runoff prediction based on imperviousness determination by spatial method. The imperviousness is defined in terms of total impervious area (TIA) and effective impervious area (EIA). The study highlights misclassification as one of the factors causing error in imperviousness determination. It is recommended that integrating GIS data with high resolution satellite imagery can be an effective solution to minimise misclassification. The predicted peak runoff was 33.4% larger when GIS based imperviousness is employed in the model. The peak runoff was 72.2% more in 2006 as compared to 1980 due to an increase in imperviousness, which is attributed to urbanisation.

Influence of initial soil condition on infiltration characteristics determined using a disk infiltrometer

The knowledge of infiltration characteristics of soil is essential for modeling flooding, artificial recharge of aquifer, mass transport through subsurface, and performance evaluation of landfill covers. A disk infiltrometer is a handy instrument for determining infiltration characteristics and permeability of the soil. Unlike the conventional infiltrometer, the disk infiltrometer can be used to control water entry into the soil at a prescribed suction. There are several numerical studies simulating cumulative infiltration vs. time response from a disk infiltrometer, where in, the initial condition of soil is important. However, there are not many experimental studies reported in the literature to understand the influence of initial compaction condition on the infiltration characteristics of soil. In this study, a mini-disk infiltrometer has been used to determine infiltration characteristics of a locally available sandy soil. All the measurements have been conducted on predetermined initial condition to understand its influence on infiltration characteristics and permeability determination. It is observed from the study that initial compaction conditions such as water content and dry density influence infiltration characteristics of soil.

Determination of Effective Impervious Area for an Urban Indian Catchment

AbstractDetermination of imperviousness, which is defined by total impervious area (TIA) and effective impervious area (EIA), is mandatory for hydrological modeling of water quantity and quality in urban areas. The determination of TIA is relatively easy and preferred to determination of EIA, even though the latter is considered to be more appropriate for hydrological studies. Accurate and representative determination of EIA requires knowledge of drainage network connectivity with the impervious surface, which cannot be ascertained from remote sensing data alone. A more realistic semiautomated direct method is suggested in this study to determine EIA by integrating the remote sensing data, the digital format of the drainage network, and a digital elevation model (DEM) of the study area. Based on the results obtained from the proposed method, a power relationship [EIA=0.0035×(TIA)2.17] relating easily measurable TIA and hydraulically relevant EIA was determined for an ungauged urban catchment in northeast ...

Relationship between peak rainfall intensity (PRI) and maximum flood depth (MFD) in an urban catchment of Northeast India

Abstract The present study demonstrates the relationship between peak rainfall intensity (PRI) and maximum flood depth (MFD) for an urban catchment in Northeast India. To study the impact of land use (LU) change and the rainfall intensities on the flooding pattern of the urban study area, the inundation maps are prepared for different LU. Also series of historical rainfall events and rainfall intensities with different return periods have been considered for the preparation of flood inundation maps. MFD has been determined from the inundation maps for all the historical rainfall events and probabilistic storms. MFD and PRI have been related to different rainfall intensities. This relationship between PRI and MFD would serve as a readymade decision-making tool for instant estimation of MFD corresponding to a given PRI and thus aid managers and decision makers to manage urban flood problem. The relation between PRI and MFD shows an exponential trend. The ratio of MFD in 2011–2006 varies between 1.06 and 1.21. The average increase in MFD from 2006 to 2011 is 1.12, which is attributed to an increase in effective impervious area from 2006 to 2011.

Indirect Determination of Effective Impervious Area (EIA) of an Urban City of North East India

Rapid urbanization and industrialization results in drastic changes in land use and land cover, which is reflected by the change in impervious area. Information regarding imperviousness is very much essential for urban hydrology and watershed management. Impervious area can further be classified into total impervious area (TIA) or effective impervious area (EIA). The most commonly used measure of imperviousness is TIA which is a measure of the area that seals water to infiltrate the down soil. Whereas EIA is that fraction of TIA that has a direct hydraulic connection to the downstream drainage. From hydrology prospective, EIA gives more accurate result than TIA and is considered as a better predictor of urbanization impact. However determination of EIA is difficult and needs high resolution satellite imageries. In the present study an attempt has been made to determine EIA of an urban city in a developing country like India making use of the space technology output. The urbanization growth pattern for 30 years has been identified from analysis of the low resolution satellite imageries employing remote sensing technique. EIA was then indirectly determined based on the land cover classification result.

A review of decision support system applications in flood management

There are several spatial problems in the water resources sector such as flood control and management, which can be managed efficiently if there is a case-based decision-making process. These types of problems need human intervention and amicable management is possible by decision making based on various possible alternatives. The recent advances in computational facilities, quick and real time access to various types of data and development in graphical user interface (GUI), have led to the frequent application of decision support system (DSS) in complex water resources management problems like flood management. This review paper summarises past efforts employing DSS, risk-based DSS and future research for DSS used in flood management. The main purpose of this review is to assess the progress made in the development of DSS and to understand how efficient it is in solving flood management problems.

Role of rainfall events and imperviousness parameters on urban runoff modelling

The volume and rate of storm water runoff in an urban watershed depend directly on the precipitation magnitude as well as its spatial and temporal distribution over the catchment. The runoff simulation may be on the basis of continuous or event wise rainfall data. Event wise simulation requires a minimum of one design-storm hyetograph as input. In contrast, continuous runoff modelling incorporates the entire meteorological record (days, months or years) of the watershed as the input. Many a time, due to the non-availability of short-interval rainfall data, a continuous simulation is performed. The present study predicts the runoff in an urban north-east Indian catchment based on event wise and continuous simulation. Continuous modelling has been performed by taking the daily rainfall data as input file. Storm water management model has been used for runoff simulation. This would help to understand the variations in urban runoff modelling due to an event based and continuous rainfall input. Green Ampt model has been used for infiltration modelling. A comparison is presented between the predicted runoff from the continuous and event wise rainfall data by considering different imperviousness parameters. The simulated runoff is overestimated by the total impervious area (TIA) that disregards the type of connectivity to the collecting network.

MODELING OF DETENTION TANK-GATE SYSTEM USING FREQUENCY AND TIME DOMAIN APPROACH

ABSTRACT A detention tank with a gate control structure has been used for improved optimization of existing drainage system by actively controlling the flow during heavy rainfall event. This can be achieved by a suitable control strategy, which is used to automatically control the gate of the detention tank based on the set of desired feedbacks. With this in view, an effort has been made in this study to develop a dynamic numerical model, which can be used to propose control strategy for the operation of gates. Further, the desired response characteristics of the detention tank, which a hydraulic engineer should look for, based on the frequency domain approach has also been discussed.

Sensitivity of imperviousness determination methodology on runoff prediction

Abstract Imperviousness in urban catchment is defined by Total Impervious Area (TIA) or Effective Impervious Area (EIA). The methodology of imperviousness determination considers its significance in terms of its connectivity and can affect the runoff determination. This paper evaluates the sensitivity of various impervious estimation methodologies on runoff prediction. Four types of imperviousness were used for distributed hydrological modeling. Green–Ampt parameters were determined through field experiments by Tension Infiltrometer. The runoff was simulated by using two indirect methods of EIA estimation and the results were compared. It was observed that the predicted runoff was 205% more if EIA estimated by indirect method was used in the model in place of EIA estimated by direct method. Also the peak runoff was found to be maximum at TIA value of 64.3%. Further TIA was found to increase the peak runoff by 398% than the runoff predicted by directly estimated EIA.