David Pezzaniti

Detention/Retention Storages for Peak Flow Reduction in Urban Catchments: Effects of Spatial Deployment of Storages

Abstract Stormwater management techniques for urban flood control have remained relatively unchanged in many practices throughout the world for most of the past 150 years. In the past 30 years, however, detention and/or retention techniques have been acknowledged as alternative approaches capable of meeting flood control objectives while providing environmental benefits and, sometimes, cost savings to developers and authorities responsible for stormwater management. In many places the use of detention and/or retention techniques has become common practice, particularly in urban catchments where open space for flood control is in short supply. This paper reports results of hydrological modelling undertaken in a hypothetical urban catchment using basic hydrographs generated by the DRAINS computer package.3 The two main aims of the modelling were 1) to explore the influence of position of retention and detention flood management elements on end-of-catchment catchment ‘peak flow’ outputs in hypothetical urban catchments, and 2) to provide clear, comparative information on the performances of the different strategies examined. The outcome from this study will not necessarily be applicable directly to all urban catchments, however it is possible that a refinement of generic flood control strategies could be developed as further related studies are undertaken in this area.

Catchment greening using stormwater in Adelaide, South Australia

The paper reviews the goals of stormwater management adopted in Adelaide and declares a focus on harvesting of stormwater to replace mains water in irrigating areas landscaped with grass, flower beds and shrubs. Four categories of catchments are recognised according to their levels of pollution production - roof runoff and “low”, “medium” and “high” pollution runoff surfaces. Four case study examples of systems involving appropriate treatment trains are described, each one delivering harvested stormwater suitable for irrigation. Two examples are given of large roof areas draining to gravel-filled trenches providing “passive” irrigation to grassed surfaces and two examples of runoff from ground-level surfaces supplying cleansed recharge to small aquifer storage/recovery schemes.

Improving Stream Low Flow Regimes in Urbanized Catchments Using Water Sensitive Urban Design Techniques

Abstract As a catchment becomes urbanised, the natural hydrological processes are significantly altered and this leads to a deterioration of the stream’s ecological condition. Low flow characteristics of a stream are useful hydrological statistical indicators for assessing the health of an ecosystem. An investigation was carried out to assess the capacity for water sensitive urban design (WSUD) measures to maintain “natural” low flow characteristics when a catchment is urbanised. A calibrated Storm Water Management Model (SWMM) of a natural catchment in South Australia was developed using historical rainfall and stream flow data. Prior to the model calibration, the sensitivity of the SWMM parameters was assessed against hydrological responses on the low flow region of the flow duration curves (FDCs) and the deficit volumes at three selected threshold flows over the calibration period. The calibrated model was then modified to generate flow data for three selected urbanised scenarios by altering the percentage of effective impervious areas. Model resolution effects on low flow regimes were assessed to ensure spatially distributed effects did not influence the results. Two selected WSUD measures were applied to one of the urbanised scenarios and low flow characteristics were examined. Flow duration and spell duration-frequency statistics of the urbanised cases were compared against those of the natural catchment. The study revealed that urbanisation causes more frequent low flow spells during both the wet and the dry seasons. As expected, the frequencies of the low flow spells with duration up to 20 days increased dramatically due to urbanisation. Both WSUD measures were capable of achieving similar frequencies for the same “natural” spell durations. The frequency of low flow spell duration events was reduced as WSUD measures were applied to the urbanised catchment case, indicating that the low flows with WSUD measures will generally be higher than those without WSUD. For the case study catchment, WSUD infiltration measures that are capable of diverting up to half of the natural groundwater input will enable low flow characteristics to be maintained.

Intercomparison testing and evaluation of sprinklers within the INITL

The International Network of Irrigation Testing Laboratories (INITL) undertook a sprinkler intercomparison testing exercise to generate data for an objective comparison of the performances of the different facilities and identify opportunities for further improvements. Three impact sprinklers were tested in four laboratories in accordance with established standards. The plots of flow rate-pressure profiles were found to be consistent, and correlated to those obtained from previous studies. Although there were slight variations in the measured flow rate data, the mean flow rates at each pressure level were the same for the three sprinklers, and the shapes of the radial distribution profiles were similar. The deviations of reconstituted flow rates (from the measured) of at least two tests in each facility were found to exceed the recommended limit. The sprinkler software developed by INITL was found to have a good correlation with a related commercial software program.

Design criteria for channel-forming flows in waterways of urbanising catchments

Adequate consideration of the joint problems of natural channel stability and bio-community preservation in greenfield catchments experiencing development has been lacking in the WSUD (water sensitive urban design) guidelines promoted in eastern and southern Australia in recent years. The paper offers retention technology as a vital ingredient of catchment management, enabling urbanisation to proceed with minimum loss of waterway environmental values.

How reliable are inlet (hydraulic) models at representing stormwater flow

Abstract It is common practice to base storm drainage network designs on gutter inlet capture information obtained from tests on hydraulic scale models. Growing interest in collection of gross pollution at inlets (‘source control’) is leading researchers to re-visit this domain of hydraulics and to question the reliability of scale models. Results from 0.4-scale and full-size models of a gutter inlet are compared in a laboratory study. Significant differences (up to 40%) were observed in flow captured, the small-scale models showing the lower values. This has important implications for pit spacing and the economics of drainage networks. Performance variation is considered to be the consequence of differences in zones of full and transition turbulence in the two model systems. This explanation is supported by differences being lower for high-flow conditions. These findings sound a warning to those using scale hydraulic models to seek solutions to the problem of ‘at source’ containment of gross pollution.