Shuffled Complex Evolution Model Calibrating Algorithm: Enhancing its Robustness and Efficiency

Shuffled Complex Evolution—University of Arizona (SCE-UA) has been used extensively and proved to be a robust and efficient global optimization method for the calibration of conceptual models. In this paper, two enhancements to the SCEUA algorithm are proposed, one to improve its exploration and another to improve its exploitation of the search space. A strategically located initial population is used to improve the exploration capability and a modification to the downhill simplex search method enhances its exploitation capability. This enhanced version of SCE-UA is tested, first on a suite of test functions and then on a conceptual rainfall-runoff model using synthetically generated runoff values. It is observed that the strategically located initial population drastically reduces the number of failures and the modified simplex search also leads to a significant reduction in the number of function evaluations to reach the global optimum, when compared with the original SCE-UA. Thus, the two enhancements significantly improve the robustness and efficiency of the SCE-UA model calibrating algorithm

Impact of short duration intense rainfall events on sanitary sewer network performance

Short duration intense rainfall causes an increase in rainfall derived infiltration and inflow (RDII) into aging sewer networks, which leads to Sanitary Sewer Overflows (SSOs). This study presents a generalised framework for assessing and mitigating the impacts of intense rainfall on sanitary sewer networks. The first part of the proposed framework involves a detailed hydraulic modelling to evaluate the performance of the sewer network. The second part deals with the development of SSO mitigation strategies based on Water Sensitive Urban Design (WSUD) approaches. This paper also demonstrates the application of the first part of the proposed framework for a case study catchment in Melbourne, Australia. The hydraulic performance of the case study sewer network during a wet and a dry year is presented. The analysis found that for the wet year, 11 manholes had sewer overflows, whereas 53 of 57 manholes in the network of 3.2 km had surcharges. Such a study will benefit the water authorities to develop mitigation strategies for controlling SSOs in their sewer systems

Prediction of Algal Bloom Using Genetic Programming

In this study, an attempt was made to mathematically model and predict algal blooms in Tolo Harbor (Hong Kong) using genetic programming (GP). Chlorophyll plays a vital role in blooms and was used in this model as a measure of algal bloom biomass, and eight other variables were used as input for its prediction. It has been observed that GP evolves multiple models with almost the same values of errors-of-measure. Previous studies on GP modeling have primarily focused on comparing GP results with actual values. In contrast, in this study, the main aim was to propose a systematic procedure for identifying the most appropriate GP model from a list of feasible models (with similar error-of-measure) using a physical understanding of the process aided by data interpretation. Evaluation of the GP-evolved equations shows that they correctly identify the ecologically significant variables. Analysis of the final GP-evolved mathematical model indicates that, of the eight variables assumed to affect algal blooms, the most significant effects are due to chlorophyll, total inorganic nitrogen and dissolved oxygen for a 1-week prediction. For longer lead predictions (biweekly), secchi-disc depth and temperature appear to be significant variables, in addition to chlorophyll

A water sustainability index for West Java - Part 2: refining the conceptual framework using Delphi technique

In the first paper of this two-part series on the development of a water sustainability index for West Java, a conceptual framework of West Java Water Sustainability Index (WJWSI) was developed. It consists of three main parts: components, indicators/sub-indicators and threshold values. This second paper of the series presents the application of the Delphi technique, followed by in-depth interviews with selected key experts, to refine the conceptual WJWSI framework. The Delphi application includes the design of the questionnaires, the selection of respondents, the distribution and collection of the completed questionnaires and the analysis of data. After Round One of the Delphi application, the respondents reached consensus for all proposed components in the conceptual framework. However, some modifications to the components were also suggested by few respondents. Regarding the indicators/sub-indicators, consensus for 9 of the proposed 12 indicators was reached, and 5 new indicators were suggested. For the threshold values, consensus was reached for threshold values of 5 indicators. In Round Two of the Delphi application, respondents were asked questions related to results from Round One, which include the modification on the components, indicators/sub-indicators which have not been agreed, and newly suggested indicators/sub-indicators and threshold values. Results of Round Two show that modifications on the components were agreed, and consensus was reached for 8 out of the proposed 9 indicators/sub-indicators. In terms of its components and indicators, the framework was then finalised in the in-depth interview with four key experts, selected from different respondent categories. For the threshold values not yet finalised, further study will be carried out, as there was not much input from the respondents in the Delphi application and the in-depth interview

A water sustainability index for West Java - Part 1: developing the conceptual framework

Sustainable water resources management is essential since it ensures the integration of social, economical and environmental issues into all stages of water resources management. The development and application of water sustainability indices to achieve sustainable water management has been successfully done in the last few years. Although existing water sustainability indices have successfully provided information on current conditions of water resources and prioritised water related issues, they have been developed for specific case study areas. This study therefore aims at developing a water sustainability index for West Java, Indonesia. The overall steps for developing the index include developing a conceptual framework, application of Delphi technique to finalise the components/indicators of the index, applying the index to case studies and robustness analysis of the index. This paper, which is the first in a two-part series, discusses the first step, namely developing the conceptual framework of the West Java Water Sustainability Index (WJWSI). It outlines the criteria for identifying the initial set of components/indicators and based on those criteria, a detailed justification for selecting each component and indicator is also presented. The second paper of the series presents the application of Delphi technique to finalise the framework of WJWSI based on feedback from selected stakeholders. The remaining steps of developing WJWSI will be undertaken in the future

Impacts of extreme rainfalls on sewer overflows and WSUD-based mitigation strategies: a review

Extreme rainfall events cause an increase in the flow into aging sewer networks, which can lead to Sanitary Sewer Overflows (SSOs). This literature review presents a complete assessment of the application of Water Sensitive Urban Design (WSUD) approaches as mitigation strategies for reducing rainfall-induced SSOs. The review highlights the various WSUD techniques identified in past studies for reducing sewer overflows. In these studies, it was identified that permeable pavements, green roofs, raingardens/bio-retention cells and rainwater tanks were the most popular WSUD strategies that have been extensively used in the past for the mitigation of sewer overflows. WSUD or “green” approaches also have enormous environmental, social and economic benefits when compared to the conventional “gray” approaches for sewer overflow mitigation. However, there have been limited studies conducted in the past that highlight and quantify the benefits of WSUD approaches for sewer overflow mitigation, particularly when such strategies are applied at a large scale (e.g., city scale). This review has identified the modelling software, SWMM, to be the most widely applied tool that has been used in the literature for WSUD modelling. It was also identified that with climate change-induced extreme rainfall events on the increase, WSUD-based “green” strategies alone may not be enough for the mitigation of sewer overflows. A suitable sewer overflow mitigation strategy could be green or a hybrid green-gray strategy, which would need to be identified based on a detailed context specific analysis

A comparative study of potential evapotranspiration estimation by three methods with FAO Penman–Monteith method across Sri Lanka

Among numerous methods that have been developed to estimate potential evapotranspiration (PET), the Food and Agricultural Organization Penman–Monteith model (FAO P–M) is often recognized as a standard method to estimate PET. This study was conducted to evaluate the applicability of three other PET estimation methods, i.e., Shuttleworth–Wallace (S–W) model, Thornthwaite (TW) and pan methods, to estimate PET across Sri Lanka with respect to the FAO P–M model. The meteorological data, i.e., temperature, relative humidity, wind speed, net solar radiation, and pan evaporation, recorded at 14 meteorologic stations, representing all climate and topographic zones of Sri Lanka, were obtained from 2009 to 2019. The models’ performances were assessed based on three statistical indicators: root mean squared error (RMSE), bias, and Pearson correlation coefficient (R). In comparison with the FAO P–M model estimates, the seasonal and annual estimates of all three models show great differences. The results suggested that pan and S–W methods perform better in the dry zone of the country. Both S–W and pan methods underestimated PET over the entire county in all seasons. TW does not show consistent results over the country, thus being found as the least reliable alternative. Although S–W is highly correlated with the FAO P–M model, the application of the model in a data-scarce region is more constrained, as it requires more parameters than the FAO P–M model. Thus, the study suggests employing alternative methods based on the region of the country instead of one single method across the entire country