Surendra Shrestha

Application of artificial neural networks in regional flood frequency analysis: a case study for Australia

Regional flood frequency analysis (RFFA) is widely used in practice to estimate flood quantiles in ungauged catchments. Most commonly adopted RFFA methods such as quantile regression technique (QRT) assume a log-linear relationship between the dependent and a set of predictor variables. As non-linear models and universal approximators, artificial neural networks (ANN) have been widely adopted in rainfall runoff modeling and hydrologic forecasting, but there have been relatively few studies involving the application of ANN to RFFA for estimating flood quantiles in ungauged catchments. This paper thus focuses on the development and testing of an ANN-based RFFA model using an extensive Australian database consisting of 452 gauged catchments. Based on an independent testing, it has been found that ANN-based RFFA model with only two predictor variables can provide flood quantile estimates that are more accurate than the traditional QRT. Seven different regions have been compared with the ANN-based RFFA model and it has been shown that when the data from all the eastern Australian states are combined together to form a single region, the ANN presents the best performing RFFA model. This indicates that a relatively larger dataset is better suited for successful training and testing of the ANN-based RFFA models.

Modelling eutrophication and microbial risks in peri-urban river systems using discriminant function analysis

The methodology currently available to river managers for assessment of river conditions for eutrophication and microbial risks is often time consuming and costly. There is a need for efficient predictive tools based on easily measured variables for implementing appropriate management strategies and providing advice to local river users on river health and associated risks. Using the Hawkesbury-Nepean River system in New South Wales, Australia as case study, a stepwise discriminant function analysis was employed to develop two predictive models, one for river eutrophication risk and the other for microbial risk. The models are intended for a preliminary assessment of a river reach, particularly to assess the level of risk (high or low) for algal bloom and whether the river water is suitable for primary contact activities such as swimming. The input variables for both models included saturated dissolved oxygen and turbidity, while the eutrophication risk model included temperature as an additional variable. When validated with an independent data set, both models predicted the observed risk category accurately in two out of three instances. Since the models developed in this study use only two or three easy-to-measure variables, their application can help in rapid assessment of river conditions, result in potential cost saving in river monitoring programs and assist in providing timely advice to community and other users for a particular aspect of river use.

An overview of on-site retention and detention policies for urban stormwater management in the Greater Western Sydney Region in Australia

This article presents an overview of on-site retention (OSR) concepts and practices as components of sustainable urban stormwater management within local government organizations (Councils) in the rapidly growing Greater Western Sydney Region. It is found that the policies regarding on-site detention (OSD), OSR and water-sensitive urban design (WSUD) vary significantly across the Councils in this region. Council specifications and guidelines are often inconsistent and inhibit sustainable urban stormwater management.

Design Flood Estimation for Ungauged Catchments: Application of Artificial Neural Networks for eastern Australia

Design flood estimation in small to medium sized ungauged catchments is frequently required in hydrological design of water infrastructure. In Australia, design flood estimation in smaller ungauged catchments is often estimated using the rational method. In recent years, there have been notable researches in Australia on the replacement of the rational method by other techniques which are hydrologically more meaningful and which can overcome the major limitations with the rational method. These methods include various forms of regression approaches and index flood methods. This paper focuses on the application of the artificial neural networks (ANN) to design flood estimation in ungauged catchments in the eastern part of Australia. This uses data from 399 stream gauging stations across eastern Australia to develop a regional flood estimation method based on the ANN. An independent test based on split-sample validation shows that the ANN can provide quite reasonable design flood estimates for small to medium sized ungauged catchments in eastern part of Australia. The best model was found to include two variables, catchment area and design rainfall intensity for the average recurrence intervals in the range of 10 to 100 years.

Study of rainwater tanks as a source of alternative water supply in a multistorey residential building in Sydney, Australia

Australia, the most urbanised population in the world, is also the driest inhabited continent with the most variable rainfall. Although Australia has the highest per capita dam storage volume in the world, reliability in water supply in Australian cities has come to question in recent years. Water has become a national issue in Australia with ever-increasing interest by politicians, media and the general public. The current storage level of the reservoirs of Sydney, which is the largest city in Australia with over 4.5 million people, is near 30%, which has resulted in the placement of Level 3 mandatory water restrictions. Sydney Water, similar to other water authorities in Australia, is desperately looking for alternative sources of fresh water including rainwater tanks in addition to recycling grey water, wastewater and the use of desalination plants. Rainwater is an alternative fresh water source that has received widespread attention in Australia in recent years. Although a rainwater tank can provide a significant volume of water to individual households and quality may not be a problem for non-potable purposes, the financial viability of a rainwater tank to individual house owners is yet to be established, in particular with the current level of subsidy for the tank provided by the government and with the current water price. There is a general lack of research on long term financial viability of rainwater tanks. This paper examines the viability of rainwater tanks in multistorey residential buildings in Sydney. Two different lot sizes (2000m 2 and 4000m 2 ) and three different scenarios were considered: 4 floors with 16 apartments and 48 persons (b) 6 floors with 24 apartments and 72 persons (c) 8 floors with 32 apartments and 96 persons. Also, the current planning method called ‘BASIX’ and the traditional approach (non-BASIX) were considered. The assumed tank size was 75kL. It has been found that is possible to achieve “pay back” for a rainwater harvesting system under some favourable scenarios and conditions. The most favourable financial conditions for the viability of the rainwater harvesting system are the 5% interest rate, the A

Investigation of design rainfall temporal patterns in the Gold Coast region of Queensland

1.634/kL water price and the 4.5% water price inflation rate. This scenario produces a cost-benefit ratio of 72%. The worst case scenario is with an interest rate of 15%, an A

Total Treatment of Black and Grey Water for Rural Communities

1.264/kL water price and a 2.6% water price inflation rate. The worst case cost/benefit produced from this scenario is 578%. The roof catchment size of the rainwater harvesting system also plays an integral part with the 2000m 2 roof area outperforming the 800m 2 roof area in terms of long term financial viability. The financial viability of a rainwater harvesting system is maximised when the water savings (or the quantity of water utilised from tanks) are high. The water savings increase with the water demand or number of occupants and whether or not the building is BASIX compliant. Thus the two best financial scenarios are for the eight-storey building and the non-BASIX approach. Capital and maintenance costs account for the majority of the expenditure over the whole life cycle cost of a rainwater harvesting system. Plumbing costs form the largest single component of the capital cost. Costs related to pump maintenance and replacement form a significant component of the total expenditure. Rainwater tank systems cannot be financially viable when the total mains top-up required is minimal i.e. when rainwater is utilised less.

Distribution of metals and speciation of sediment grabs in Lake Burragorang in Sydney, Australia

Abstract Design rainfall temporal pattern is a major source of uncertainty in rainfall-based design flood estimation methods. The Australian Rainfall and Runoff 1987 (ARR87) adopted the Method of Average Variability to derive design rainfall temporal patterns for Australia. It is assumed that the use of these temporal patterns along with representative values of other inputs to the rainfall runoff modeling can preserve the frequency of input rainfall depth in the final flood peak estimate. Although this assumption is questionable, the use of more holistic approach of design flood estimation such as Monte Carlo simulation technique or continuous simulation has not yet been widely accepted by the industry. It will take a while to develop design data and application tools for application with the Monte Carlo simulation and continuous simulation techniques and hence the ARR87 design temporal patterns will remain in use with the Design Event Approach for a while. This paper presents a simple windows-based tool that can be used with sufficient ease to derive design temporal patterns from region-specific data of longer lengths adopting the Method of Average Variability, the ARR87 procedure. This windows-based tool is applied in the Gold Coast region in Queensland to derive new design temporal patterns and it is found that the ARR87 design temporal patterns for the Gold Coast region result in significantly smaller estimated design floods for larger duration storms as compared to the newly derived design temporal patterns.

Rainfall Energy Loss: An Empirical Model

Decentralized or on-site treatment systems for domestic waste and wastewater treatment can be the answer to many of the world’s environmental health problems. Poor or remote communities need technologies developed for the application, and an economically viable whole-of-waste approach is necessary. Vermicomposting offers a natural option to treat domestic waste and wastewater into reusable products. The extent of treatment can be incorporated into the design, providing flexibility and scalability required for the user community.

Regional flood modelling : use of Monte Carlo cross-validation for the best model selection

Lake Burragorang in South-West Sydney, holding 2.1 billion litres of water, is the principal source of drinking water supply for 4.5 million Sydney residents. The Wollondilly, Nattai, Kowmung and Coxs are the four major tributaries that provide approximately 83% of total inflow into the lake. Each of these tributaries has catchments with substantially different geology and hence the sediment loads contributed by each of these rivers have their own characteristics. As a part of the water quality analysis within lake Burragorang, sediment grabs were extracted from the lake bottom (from pre-selected locations) with a view to determine spatial variation of sediment characteristics across the lake. A total of eleven sites were chosen for sequential extraction of sediment grabs. Samples were analysed to determine distribution and speciation of 14 selected heavy metals (from 11 sites) in bed sediments. The results were correlated with the geological and human histories of the local catchments and reservoir operations. A consistent general trend in metal concentration variation was observed. Some sites showed lower concentrations of metals than the background level whereas other sites indicated metal concentrations to be far higher than the background level. These were found to be related to previous mining activities. In general, no significant spatial variations were observed in the speciation trends.