On-site reduction and attenuation of urban stormwater runoff

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Mantle, J.D.G., 1993. On-site reduction and attenuation of urban stormwater runoff. PhD, Nottingham Trent University.

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Abstract

The continued construction of impermeable surfaces, such as roads and roofs, has led to overloading and flooding of conventional urban drainage systems by stormwater runoff. Natural recharge of groundwater through infiltration is also limited. One possible solution to such urban drainage problems is to reduce or attenuate all or part of the storm inflow. This may be achieved by either: infiltrating the runoff directly into the ground; or, routing the runoff through a permeable pavement and thence to groundwater or conventional drainage. U.K. field research in this subject has been extremely limited.

The research project reported herein, based at The Nottingham Trent University, evaluated a number of reduction and attenuation structures suitable for 'on-site' use. The structures built were: a 160m2 permeable pavement used as a car park; and three infiltration devices which received roof runoff, (a stone-filled soakaway, a dual-chambered soakaway and an infiltration trench). The rainfall, runoff and storage relationships of these structures were monitored for a period of two years.

Real-time observation and testing of the hydrological characteristics of an engineered permeable pavement, surfaced with concrete blocks, demonstrated the structure to be effective at both reducing and attenuating the rainfall hyetograph. 'Runoff' was monitored as discharge from a sealed sub-base 'tank'. Incident rainfall was subject to absorption into the concrete block surface and upon the sub-base stones: evaporation returned these 'rainfall losses' to the atmosphere. Attenuation of the runoff peak was achieved as flow percolated through the device: runoff frequently continued for many hours or days after rainfall. The sub-base stones affected the magnitude of runoff by virtue of their texture and grading: of the stones trialled, blast furnace slag proved particularly effective. 'Runoff' was typically an average of 30% to 50% of rainfall.

Analysis of the monitored data, and the results of several small-scale tests, enabled the generation of a physical/conceptual loss model which demonstrated that rainfall depth was the most significant determinant of runoff volume: rainfall duration was also significant as 'loss processes' were time-dependent. Antecedent conditions controlled the volume of storage available at the beginning of an event and were also demonstrated to be significant in determining runoff volume. Statistical regression analysis indicated that the data set contained strong predictive qualities which may be used for determining runoff parameters. However, the natural rainfall 'input' to the model was generally far from extreme, and care must be taken before the models are used for 'design' events on similar urban surfaces.

Long-term monitoring of roof runoff inflow to, and storage within, infiltration devices has established that such devices may successfully infiltrate runoff in poor, silty-clay, soil conditions. The calculated infiltration rates exceeded those indicated by borehole percolation tests, (commonly used as dimensioning methods). Repeated borehole testing showed large seasonal variations to calculated infiltration rates.

The design, maintenance and philosophy relating to on-site stormwater reduction and attenuation practice for various countries is examined in the light of the experimental data and experience. Wider use of stormwater reduction and attenuation practice for various countries is examined in the light of the experimental data and experience. Wider use of stormwater reduction and attenuation methods are recommended as part of urban stormwater management strategies.

Item Type:

Thesis

Creators:

Mantle, J.D.G.

Date:

1993

ISBN:

9781369324594

Identifiers: