Joe McMahon

Urban Water Mass Balance Analysis

Planning for “water‐sensitive” cities has become a priority for sustainable urban development in Australia. There has been little quantification of the term, however. Furthermore, the water balance of most cities is not well known. Following prolonged drought, there has also been a growing need to make Australian cities more water self‐reliant: to source water from within. This article formalizes a systematic mass‐balance framework to quantify all anthropogenic and natural flows into and out of the urban environment. Quantitative performance indicators are derived, including (1) degree of system centralization; (2) overall balance; potential of (3) rainfall, (4) stormwater, and (5) wastewater to offset current demand; and (6) water cycle rate. Using the method, we evaluate Sydney, Melbourne, South East Queensland and Perth using reported and modeled data. The approach makes visible large flows of water that have previously been unaccounted and ignored. It also highlights significant intercity variation. In 2004–2005, the cities varied 54% to 100% in their supply centralization, 257% to 397% in the ratio of rainfall and water use, 47% to 104% in their potential stormwater recycling potential, and 26% to 86% in wastewater recycling potential. The approach provides a practical, water‐focused application of the urban metabolism framework. It demonstrates how the principles of mass balance can help foster robust water accounting, monitoring, and management. More important, it contributes to the design and quantitative assessment of water‐sensitive cities of the future.

An investigation of controlling variables of riverbank erosion in sub-tropical Australia

A large proportion of the uncertainty surrounding catchment sediment budget modelling has been attributed to sediment supplied from riverbank erosion. Some of the variables influencing riverbank erosion are bend curvature, specific streampower, riparian vegetation, and in some instances sand and gravel extraction. The empirical relationship between these variables and observed riverbank erosion across 78 km of the Upper Brisbane River, Australia was investigated. No significant relationship was found between curvature, specific streampower and riverbank erosion. The role of riparian vegetation relative to sediment supply from riverbank erosion varied with spatial location, susceptibility of a reach to erosion, and human disturbance such as sand and gravel extraction. Despite not having data on substrate type the model described approximately 37% of the variation in observed riverbank erosion. It appears that inclusion of a management practice factor in riverbank erosion models is justified, where appropriate, and may improve model performance.

An alternative method for interpreting jet erosion test (JET) data: Part 2. Application

This paper reports the results of jet tester experiments on soil samples of uniform properties which allow quantitative application of the new theory proposed in part 1 of these publications. This theory explores the possibly that a more adequate indicator of soil erodibility may be obtained by using the mass (and so volume) of soil eroded by the jet and the depth of scour penetration, rather than by using penetration depth alone, as assumed in the commonly-used data interpretation method. It is shown that scour geometry can be well described using a generalized form of the Gaussian function, defined by its standard deviation and maximum depth. Using a published expression for jet kinetic energy flux, the new theory divides this flux into that used to erode soil, and the remainder which is dissipated in a variety of ways. Jet experiments on a specially-prepared uniform soil sample are reported which provide the key to determining the spatial variability in the profile resistance to erosion offered by field soils. This resistance is expressed in the work required to erode unit mass of soil, denoted as J (in J/kg). The paper also gives results obtained on the profile variation in J for jet tests carried out at riverine sites on the upper Brisbane River, Queensland, Australia. As expected in most natural soil profiles, the results show an increase in J with depth in the profile. The soil resistance (J) is compared to the traditional interpretation of soil erodibility, (kd). The graphical comparison of these two indicators illustrates the inverse type of relationship between them which is expected from their respective definitions, but this relationship is associated with significant scatter. Possible reasons for this scatter are given, together with comments on jet tester experience in a wide variety of soil types. Copyright