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© Copyright © 2020 Ball. Catchment management is a complex task that, over the past decade, has become increasingly important to urban communities. While there are many water related management issues, estimation of the magnitude and likelihood of flood events is one that remains a concern to many mangers of urban drainage systems. Data is an essential component of any approach for estimation of the magnitude and likelihood of design flood characteristics. This data can be obtained from catchment monitoring or catchment modeling with these data sources being complementary rather than competitive. However, the absence of monitored data in urban environments has resulted in the data being obtained predominantly from the use of catchment modeling. Numerous alternative approaches for catchment modeling have been developed; these approaches can be categorized as either single event or continuous models. The philosophical basis behind the use of a continuous modeling approach is the concept that the model predictions will replicate the data that would have been recorded if catchment monitoring were to be undertaken at that location and for the modeled catchment conditions. When using this philosophy, a modeler must determine when the predicted data suitably replicates the true data. Presented herein is an analysis of continuous and event modeling undertaken for design flood estimation in an urban catchment located in Sydney, Australia where monitored data is available to assess the utility of the catchment model. It will be shown that frequency analysis of the predicted flows from the continuous model more closely resemble the frequency analysis of the recorded data.

© 2018 by the authors. In the last few decades tremendous progress has been made in the use of catchment models for the analysis and understanding of hydrologic systems. A common application involves the use of these models to predict flows at catchment outputs. However, the outputs predicted by these models are often deterministic because they focused only on the most probable forecast without an explicit estimate of the associated uncertainty. This paper uses Bayesian and Generalized Likelihood Uncertainty Estimation (GLUE) approaches to estimate uncertainty in catchment modelling parameter values and uncertainty in design flow estimates. Testing of join probability of both these estimates has been conducted for a monsoon catchment in Vietnam. The paper focuses on computational efficiency and the differences in results, regardless of the philosophies and mathematical rigor of both methods. It was found that the application of GLUE and Bayesian techniques resulted in parameter values that were statistically different. The design flood quantiles estimated by the GLUE method were less scattered than those resulting from the Bayesian approach when using a closer threshold value (1 standard deviation departed from the mean). More studies are required to evaluate the impact of threshold in GLUE on design flood estimation.

© Proceeding of the 21st LAHR-APD Congress 2018. All rights reserved. This study is presented to estimate net soil infiltration and groundwater recharge in Sukhuma District of Southern Laos. A soil water balance approach is used to estimate the net infiltration from the Tropical Rainfall Measuring Mission (TRMM) and Global Land Data Assimilation System (GLDAS) data. The groundwater recharge is estimated by using the water table fluctuation method from observation groundwater levels at eleven domestic wells and five paired observation wells (shallow and deep). The results show that average annual net infiltration flux from 2000-01 to 2015-16 is decreasing at a rate of 6 mm/year. For the same period of the net infiltration flux, the average annual rainfall derived from TRMM for the Sukhuma District also depicts a declining trend with a rate of 26 mm/year. A value of specific yield for the shallow fractured sandstone aquifer in the Sukhuma District is quantified at approximately 0.03. Groundwater recharge for 2012-13 and 2015-16 is estimated at 5% (118 mm) and 4% (95 mm) of annual rainfall, respectively. The net infiltration estimated from GLDAS and TRMM data shows reasonable agreement with the ground-based measurements. The results of the current study provide useful basic information for future groundwater resource management planning in Sukhuma District. The methods applied in this study may be also useful for studying the soil infiltration and groundwater recharge in regions with limited field data.

© Proceeding of the 21st LAHR-APD Congress 2018. All rights reserved. In the absence of monitored data from an urban catchment, modelling of the catchment is an accepted methodology for generating data necessary for the management of those systems. The catchment modelling systems used to generate the data are not exact and hence the generated data will contain errors. The purpose of model calibration is the minimisation of these errors. While these errors can be developed from a variety of sources, it is the errors arising from parameter values that usually are the focus of the calibration process. Presented herein is a discussion focussing on urban catchments of issues associated with parameter value identification in distributed catchment modelling systems.

Since its first publication in 1958, Australian Rainfall and Runoff (ARR) has remained one of the most influential and widely used guidelines published by Engineers Australia (EA). The 3rd edition, published in 1987, retained the same level of national and international acclaim as its predecessors. With nationwide applicability, balancing the varied climates of Australia, the information and the approaches presented in Australian Rainfall and Runoff are essential for policy decisions and projects involving: infrastructure such as roads, rail, airports, bridges, dams, stormwater and sewer systems; town planning; mining; developing flood management plans for urban and rural communities; flood warnings and flood emergency management; operation of regulated river systems; and prediction of extreme flood levels. However, many of the practices recommended in the 1987 edition of ARR have become outdated, and no longer represent the accepted views of professionals, both in terms of technique and approach to water management. This fact, coupled with greater understanding of climate and climatic influences makes the securing of current and complete rainfall and streamflow data and expansion of focus from flood events to the full spectrum of flows and rainfall events, crucial to maintaining an adequate knowledge of the processes that govern Australian rainfall and streamflow in the broadest sense, allowing better management, policy and planning decisions to be made. One of the major responsibilities of the National Committee on Water Engineering of Engineers Australia is the periodic revision of ARR. While the NCWE had long identified the need to update ARR it had become apparent by 2002 that even with a piecemeal approach the task could not be carried out without significant financial support. In 2008 the revision of ARR was identified as a priority in the Council of Australian Governments endorsed National Adaptation Framework for Climate Change. In addition to the update 21 projects were identified with the aim of filling knowledge gaps. Funding for Stages 1 and 2 of the ARR revision projects were provided by the now Department of the Environment. Stage 3 was funded by Geoscience Australia. Funding for Stages 2 and 3 of Project 1 (Development of Intensity-Frequency-Duration information across Australia) has been provided by the Bureau of Meteorology. The outcomes of the projects assisted the ARR Editorial Team with the compiling and writing of chapters in the revised ARR. Steering and Technical Committees were established to assist the ARR Editorial Team in guiding the projects to achieve desired outcomes.

A reliable and comprehensive flood warning system is one of the key factors to minimize damage and disruption create by a flood. Ganges and Brahmaputra is the major river system of Bangladesh and authorities of Bangladesh use gauging data of this two rivers for their flood forecasting. This study only focuses on Brahmaputra River, which is still a morphologically very active river. This paper discusses how the prediction can be biased using conventional method for flood prediction, i.e. using only stage-discharge relationship. In this study, we used 1,687 observations (discharge, water level, river width and cross-sectional area) at Bahadurabad station of Brahmaputra River selected from 1976 to 2009. We examined the stationarity of river cross-section and water level-discharge relationship. The study shows that the relationship between water level and river flow changes every year significantly and without any indication which way it may change in the next year. The relationship of stage discharge is so wide that the river may experience approximately double of the calculated flow. Therefore, river water management and flood forecasting would require comprehensive method rather than relying only on stage discharge correlation. Moreover, there is also trend in river geometry which may create more uncertainty in flood forecasting.

© 2016 International Association for Hydro-Environment Engineering and Research. Estimation of design flood flow has been and remains a concern for both hydrologic research and hydrologic practice. Knowledge of design flood flows provides a basis for sustainable flood management, which has the aim of reducing flood risk, thereby protecting people’s lives and property. Design floods for a given location can be estimated by a number of approaches including analysis of past flood statistics and the use of catchment modelling. When catchment modelling approaches are applied estimation of design flood flows, there is a need to calibrate the model parameters. As part of this calibration process, a calibration metric, or fitness measure, is needed to enable assessment of alternative sets of parameter values. Presented herein is an investigation into design flood quantiles derived from predictions obtained from a continuous catchment modelling system when alternative calibration metrics are used to assess the suitability of parameter values. Two alternative calibration metrics are considered with one calibration metric aimed at ensuring replication of recorded hydrographs and the second calibration metric aimed at ensuring replication of the statistical characteristics of the annual maxima series. It was found that use of the later calibration metric resulted in better reproduction of the flood probability model estimated from the historical data while reproduction of the recorded hydrographs (i.e. the first calibration metric) did not ensure reproduction of the flood probability model.

© New Zealand Hydrological Society (2017). Sparse hydrogeological data is a significant limitation to the study of groundwater in many areas. The objective of this study was to assess the hydrogeology in Sukhuma District of Champasak Province in Southern Laos where such a limitation occurs. The connection between surface water and groundwater was assessed by comparing groundwater levels and river bed elevations. Groundwater recharge was estimated by the water table fluctuation method. The feasibility of remote sensing to address data limitations for the future study of groundwater in the region was also investigated by comparing the Mekong River flow and rainfall data with the Equivalent Water Height derived from the Gravity Recovery and Climate Experiment; soil moisture data obtained from the Global Land Data Assimilation System was also compared with rainfall and groundwater levels in Sukhuma District. The results show that some parts of Khamouan River bed are disconnected from the water table during the dry season, whereas the river bed is fully connected to the water table during the wet season. However, in the Pheung River, which flows into the Khamouan River upstream of the river gauge, the groundwater level is fully disconnected from the river bed in the dry season and partially connected in the wet season. Groundwater recharge estimates vary according to the specific yield values used for the aquifer. The comparison between in-situ hydrological measurement and remote sensing data provides insights into the general hydrogeological conditions. The comparison also provides useful information for future studies of the hydrogeology in Sukhuma District and Southern Laos, where field observation data are sparse, to support sustainable groundwater development in the region.

Design flood estimation remains a problem for many professionals involved in the management of rural and urban catchments. An essential aspect of this problem is prediction of the magnitude of the hazard and the exceedance probability of the hazard from suitable data. This suitable data can be obtained from either monitoring of the floods in the catchment or from catchment modelling aimed at replicating floods that would have been monitored were monitoring systems in place. If the suitable data is obtained from monitored data, then the predictions are obtained from a frequency analysis of the monitored data. If the suitable data is generated by catchment modelling, then monitored data is needed to ensure application of the catchment modelling system results in flood predictions that are suitable replications of the data that could have been recorded at the site of interest. In both cases, there is a need to ensure the reliability of the gauged data in terms of flood flows. A typical gauging station, however, monitors river stages and requires a stage-discharge relationship to convert the recorded levels to an equivalent flow. For design flood systems, extrapolation of the stage-discharge usually is required. There is a need to consider the impact of this extrapolation of the stage-discharge on the predicted flood. Presented herein will be the results of an investigation into stage-discharge relationships and design flood estimation.

© 2017 Engineers Australia. All Rights Reserved. Southern Laos is undergoing economic and agricultural development, resulting in a large increase in groundwater and surface water use. However, these water resources are not known in detail. This study aims to investigate the groundwater and surface water interactions in the Sukhuma District of Champasak Province using a network of sixteen rain gauges and groundwater levels measurement points. Groundwater levels are measured weekly in eleven domestic wells, which are pumped irregularly, and also in five observation bores. Aquifer recharge occurs from direct infiltration of rainfall and also is derived using baseflow calculated from daily streamflow measurements at the re-established gauging station on the Khamouan River in Sukhuma District. The Khamouan River is connected to the groundwater in its lower reaches in both dry and wet seasons. Baseflow proportion to the total streamflow in the wet season 2015 has been estimated at 46%. The distribution of direct recharge has been mapped with ArcGIS and is spatially variable. Preliminary estimates of rainfall recharge have been calculated by the water table fluctuation method for 2015 but show a high degree of uncertainty related to the specific yield estimates. Time series analysis has confirmed the observed lag of some three to four weeks between the wet season start and rise in groundwater levels. These preliminary results indicate that there is close interaction between groundwater and surface water in the Sukhuma District. Further analysis will refine these results and extend them through remote sensing across southern Laos for application to integrated water resources management.

© 2015, Engineers Australia. All rights reserved. Flood is a common phenomenon in many tropical countries. Estimation of design flood flow has been a concern for many years in both hydrologic research and in hydrologic practice. Design flood magnitudes provide a basis for sustainable flood management which has the aims of reducing flood risk, and protecting people's lives and property. Design flood magnitudes for a given location can be estimated by a number of approaches including analysis of past flood statistics or the use of catchment modelling approaches like design storm methods or continuous simulation. The aim of this paper is to apply Annual Maximum Series fitting method for design flood estimation in continuous simulation with particular reference to a monsoon catchment. In this aspect, the annual maximum series was used as a performance measure rather than reproduction of individual hydrographs. This approach was used as the focus was on reproducing the observed frequency curve. For this purpose, a case study is performed for a large catchment, namely the Ba River, located in central Vietnam. This catchment is subject to a monsoonal climate and also to tropical cyclones.

© 2015, Engineers Australia. All rights reserved. Reliable and efficient design flood estimation remains a concern for many catchment managers. The search for reliable and efficient approaches to design flood estimation together with the increased computational capacity available to analysts has resulted in the development of computationally intensive methods for design flood estimation; for example, the application of a Genetic Algorithm for calibration of a catchment modeling system and the use of a Monte Carlo technique for generation of a POT series requires multiple executions of the catchment modeling system. As the execution of a given simulation is entirely separate from others, the computation step in the method is embarrassingly parallel. The key step to reduce computational run times, therefore, is to efficiently distribute, compute and gather the results amongst a cluster of computers or processing cores. Within this paper we present two methods of efficiently distributing the individuals such that they are computed in parallel. The example application is the use of a Genetic Algorithm for calibration of SWMM applied to an urban catchment. The first method is based on the recognition that SWMM 4.4 is a single threaded application. We can, therefore, place a wrapper that is multi-threaded in front of the SWMM execution step and compute the population in parallel on a multi-core machine. With this wrapper we achieved linear speed up to three cores, which peaked at a 5.5 times speed up on 12 core machine. The second method builds on the first and is based on the BOINC framework. Implementing a distributed methodology to deploy the multi-core programme across a cluster of shared workstations using the BOINC middleware, we were able scavenge 20-30% of the computational resources of a 100+ node cluster with over 1000 cores.

Rainfall is one of the more important factors influencing flows in a river and particularly so for flood flows in a river. Hence there is a need to adequately model rainfall if flows in rivers are to be predicted with reliability. There are three components to a rainfall model, namely the rainfall depth, the spatial distribution of rainfall and the temporal distribution of rainfall. This last aspect of a rainfall model is the focus of the study that will be presented in this paper. In many Asian countries, the data for assessing the sub-daily temporal distribution of rainfall is limited by the availability of continuous records. It is far more common for the available data to comprise daily rainfall records. There is a need, therefore to disaggregate these daily rainfall records. One method that has been applied to the problem of disaggregation of daily rainfall records is the "Method of Fragments". Presented herein will be a discussion of the application of the "Method of Fragments" to the disaggregation of daily rainfall records in a monsoonal catchment in Vietnam. The case study catchment is the Ba River where 14 daily-read gauges and 12 hourly rainfall stations across the basin were available. The similarity of statistical characteristics of these gauges was evaluated by Welch Two Sample t-test and Bartlett test of homogeneity of variances. The model is validated at 3 stations, where recorded hourly data was available. Hourly rainfall of 14 stations is then disaggregated from daily data based on the historical observed hourly data from 12 hourly stations in the basin.

Design flood estimation remains a problem for many engineering hydrologists. Advice is required regarding design flood characteristics for design of culverts and bridges, urban drainage systems, flood mitigation levees, dam spillways, and many other situations. The important flood characteristic depends on the nature of the problem, but typically is either the peak flow rate, peak level, hydrograph rate of rise, flood volume, or system failure. As discussed by Ball et al. [2], a common approach for estimation of the peak flow is application of catchment modelling systems with the frequency of rainfall intensity transferred to the predicted peak flow rate. This approach assumes the temporal variability of rainfall does not influence the frequency transferral. Using rainfall temporal patterns generated using the approach of Varga et al. [12], 60 alternative non-dimensional patterns were generated. These alternative temporal patterns were combined with the Intensity-Frequency-Duration information at Sydney to generate storm bursts over the full range of frequencies, namely AEPs of 50% to 1%. The resultant storm bursts were applied to a SWMM based model of the Centennial Park catchment in Sydney Australia. Predicted flows for the various frequencies were analysed to ascertain the variability in the predicted peak flow arising from the temporal pattern of the rainfall and hence the validity of the assumption that the temporal pattern of rainfall does not influence the transferral of the rainfall frequency to the predicted flow frequency. Presented in this paper are the results of an investigation into the validity of this assumption.