Browsing by Author "Wanniarachchi, S. S"

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Embargo
Challenges in field approximations of regional scale hydrology
(Elsevier, 2020-02-01) Wanniarachchi, S. S; Wijesekera, N. T. S
Study region Considering the availability of gauged data, the Karasnagala watershed of Attanagalu Oya located in the Gampaha district in the Western province of Sri Lanka was modeled with EPA SWMM 5. Study focus This study analyses the effect of the catchment field approximations for accurate flood hydrograph prediction. Following an event based approach, 3 days Minimum Inter event Time (MIT) and 0 mm/day Minimum inter Event Depth (MED) were used as the threshold. Fifty events were separated from 1971 to 1982 period. Four major field approximation types were identified: stream geometrical parameters approximations, soil infiltration parameter approximations, approximation of watershed intermittent storages, and subcatchment delineation approximation. Soil parameter approximations and the stream network geometry parameter approximations were verified by the field observations. New hydrological insights for the region Model calibration and verification revealed that EPA SWMM5 can be successfully used to develop regional Karasnagala watershed model with mean ratio of absolute error (MRAE) 0.289 for calibration, and 0.375 MRAE for verification. Incorporation of intermittent storages with optimized model layout obtained the best fitting of hydrograph recession MRAE 0.167. Subcatchment lumping with a 16 sub basin configuration showed the marginal increment of modeling error when compared with distributed modeling. Stream parameter approximations revealed that the head water streams/lesser order streams parameters sensitivity is higher than that of the higher order streams. In soil parameter approximations, saturated hydraulic conductivity of the soil was the most influencing parameter.
Open Access
Importance of hydrologic simulation for LIDs and BMPs design using HEC-HMS: A case demonstration
(Medcrave, 2017) Khaniya, B; Wanniarachchi, S. S; Rathnayake, U
Best management practices (BMPs) and the Low impact development (LIDs) is water management tools used to mitigate hydrological impact resulting from unpremeditated urbanization. For the proper functioning of the LID and BMP features the volume of the runoff generated, peak runoff rate before and after the installation, need to be accessed. Modeling by comparing different developmental scenarios helps to characterize the impact of BMPs and LIDs practices on the surface runoff. Therefore, this paper describes a modeling approach to predict the performance of these BMPs and LIDs in an existing hydrological model. This type of modeling approach is important to understand the long-term operation of the watershed post-development plan. A single rainfall event in May 2013 has been modeled and the characteristics graphs such as outflow, precipitation, runoff, infiltration have been analyzed. Run-off volume after retrofitting infiltration trench has decreased by 351m3 at the outlet with an increase of 39 L/s in peak discharge. Time series study of reservoirs depicts low performance of infiltration trench at latter phase of rainfall event. This leads with a rational that infiltration trench cannot result favorable for longer rainfall events unless underlying soil has superior geo-technical properties with low level water table. Results manifest the benefits of using hydrologic modeling software to understand the watershed hydrology.
Open Access
Sustainable stormwater management system: a conceptual design model for SLIIT, malabe campus, Sri Lanka
(Faculty of Engineering, Sri Lanka Institute of Information Technology, 2016) Khaniya, B; Wanniarachchi, S. S; Rathnayake, U. S
In recent years, significant attention has been given to the utilization of water and its components. Management of the wastewater including run-off to maintain a balanced eco-system has been an irony issue mostly in urban areas. Conventional water management systems such as reducing peak flow rate, sewer systems, end of pipe mitigation measures do not tend to fulfill the tortuous developmental plan of growing cities. It is therefore, necessary to use the principle management concepts such as best management practices (BMPs), low impact developments (LIDs) focusing on micro-management design concepts to intensify the existing hydrological cycle. Structural practices such as perforated infiltration trench along with bio-retention pond is thought to control the storm water at Sri Lanka Institute of Information Technology (SLIIT) premises based on the biophysical, hydrological and ecological ascribes of the landscape. This was identified as a critical issue to the well-being of the students during the rainy periods. Impervious layers introduced in aesthetic purposes have reduced the infiltration and then, increase the temporary flooding / pooling of these impervious surfaces. Post-development water management requires multi-disciplinary understanding of watershed along with identification of predevelopment functions and their constraints. Therefore, parameters of soil properties like permeability, grain size, and other parameters like soil profile analysis, water quality analysis, water table depth, soil moisture condition and trench geometry based on terrain at two different sites were analyzed. Field tests were performed to find infiltration rates to compute the performance of the trench and to determine the storage volume based on rainfall events. Thus, this paper imparts colors upon an affordable, pragmatic and long-term solution to meet the need of modern water management at SLIIT. An infiltration trench network is being proposed to overcome the flooding / pooling problems in SLIIT premises and the proposal is being presented to the management of the institution.