Comparison of direct rainfall and lumped-conceptual rainfall runoff routing methods in tropical North Queensland – a case study of Low Drain, Mount Low, Townsville

Johnson, Peter (2013) Comparison of direct rainfall and lumped-conceptual rainfall runoff routing methods in tropical North Queensland – a case study of Low Drain, Mount Low, Townsville. [USQ Project]

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Abstract

As rain falls on a catchment, some of it will soak into the ground, some will be stored in small depressions, leaving the remainder to run along the surface as runoff. Flood modellers use a variety of software to analyse the way in which runoff behaves across a surface. Modelling has traditionally been undertaken in two components, hydrologic and hydraulic analysis. Hydrologic analysis enables the analyst to quantify the flow of water within a watercourse, by typically using lumped-conceptual runoff routing models. The hydraulic analysis uses the flow predictions of the hydrologic model to define the mechanisms of flow along watercourses and across floodplains. Within the last 10 years, 2D hydraulic modelling has become more popular with increasing flexibility, robustness and computational power. Its ability to apply rain directly to a 2D grid, known as the direct rainfall method (DRM), has provided for explicit modelling of catchments. Despite its popularity, there are differences between the models that are yet to be confirmed and explored by the industry.

Traditional lumped-conceptual models are broadly accepted in the industry due to their long history of use, and their successful calibration in a wider selection of gauged catchments. It is therefore unreasonable for one to assume that traditional lumped-conceptual approaches are being superseded by the DRM, despite it having increased popularity. Research is unfortunately limited for the popular growing DRM. Poor understanding of its intricacies have resulted in uncertainties toward its use. Parameters from traditional methods, such as rainfall losses, are being used to conceal uncertainties in the DRM. This project is important to the stormwater industry, as it provides practical value on the use of the DRM. Its findings extend on previous research by exploring the effects of catchment parameters, and also build on research, by investigating further effects for various storm durations.

A series of flood models were tested on a catchment, and three of its internal sub-catchments. The peak magnitude and timing of runoff results were compared between the DRM and lumped-conceptual models, being MIKE FLOOD and XP-RAFTS respectively. These analyses were explored over a range of storm duration events. Sensitivity testing of rainfall losses, catchment roughness, and wetting & drying, were undertaken so as to understand the effects of each of these parameters in the DRM.

Modelling and analysis were made possible through the use of both traditional and leading-edge engineering techniques, methods, and software tools. This project successfully highlights the components responsible for differences in catchment runoff behaviour between the DRM and lumped-conceptual model. The findings illustrate the effect storage has on reducing and attenuating runoff within the DRM, especially for short duration storm events, when compared to the lumped-conceptual model. These findings are unique, being the first known to be presented to this extent to the engineering industry. The sensitivity testing on the DRM complimented previous research, showing that lower rainfall losses, and roughness values, result in higher runoff.

Further investigations into the effect of storages, fraction impervious and slope, as well as many other components, are yet to be expanded by the industry.
This project contributes to the much needed insight into the DRM, when compared to lumped-conceptual models. The sensitivity analyses provide for practical awareness of
parameters, whilst the modelling over a variety of storm durations indicates major differences of runoff peaks and times when compared to lumped-conceptual models. It is unreasonable to say one method is superior to the other, as it is known that both methods have been successfully calibrated and verified to actual events. This project rather reveals the differences that modellers may encounter during use of the models, and justifies some of the reasons for them.


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Item Type: USQ Project
Item Status: Live Archive
Faculty / Department / School: Current - Faculty of Health, Engineering and Sciences - School of Civil Engineering and Surveying
Supervisors: Brodie, Ian
Date Deposited: 06 Mar 2014 05:59
Last Modified: 06 Mar 2014 05:59
Uncontrolled Keywords: comparison; direct rainfall; lumped-conceptual runoff; low drain; townsville; flood models
Fields of Research : 09 Engineering > 0905 Civil Engineering > 090509 Water Resources Engineering
URI: http://eprints.usq.edu.au/id/eprint/24632

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