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Hydraulic residence time of a stormwater pond with different vegetation and discharge

Researcher: Visoth Tiev
Project duration: 2007-2010
Supervisor: Prof. Ian Guymer
Funding body: Warwick Postgraduate Fellowship

Project Description

Constructed and Natural Wetlands have been widely used to manage water resources. They have been used as recipients of stormwater runoff, including that which drains agricultural lands and urban developments. Unlike wastewater wetlands, where a high degree of engineering is adopted in creating an efficient shape, the stormwater pond must often fit into existing water courses and this may lead to pond layouts that are less than ideal from a hydraulic point of view. To determine expected water quality improvements, it is essential to understand quantitatively various options to optimise flow paths and maximise the hydraulic residence time. Pond hydraulics is very important to understand its influence of physical, chemical and biological mechanisms throughout the pond system. Finney and Middlebrooks (1980), stated “the hydraulic detention time is used in many [media][/media]of the design methods; it is recommended that future research on pond performance consider the effect of physical and climatic conditions on hydraulic residence time. Once residence time can accurately be predicted, perhaps present design methods can be modified to predict pond performance satisfactorily”. This research aims to accurately model the solute hydraulic residence time (HRT) of a natural stormwater pond using a physical scale model and investigate how this varies with different conditions such as discharges and vegetation. HRT is one of the important parameters and act as efficiency indicators of natural ponds.

Research Needs and Aims of the Thesis

The aim of this study is to understand the influence of discharge and vegetation on the hydraulic residence time of a natural pond. To achieve this aim, firstly, the whole year cycle has been investigated on a full scale field-pond located in Sweden (Figure 1) and secondly detailed studies on a physical scale laboratory model (Figure 2) has been performed. This will provide a data set quantifying the influence of discharge and vegetation on the HRT for both lab scale and full scale field application. The research aims to demonstrate a method for determining a meaningful concept of residence time of natural pond which would be suitable for an engineer to assess the design of treatment processes. Field pond hydraulics has been quantified in term of discharge, water level and vegetation type and cover on the pond.

figure_1__lyby_field_pond_constructed_july_2001_sweden.jpg   figure_2__laboratory_scale_pond_at_warwick_university.jpg
Figure 1: Lyby field pond constructed in July 2001, Sweden.  
Figure 2: Laboratory scale pond at Warwick University


The two films on this page show surface flow in scale pond, without vegetation (left) and with vegetation (right).


Movie 1: Surface flow in scale pond, without vegetation.

Movie 2: Surface flow in scale pond, with vegetation.


References

Duncan, H.P. (1997) Urban Stormwater Treatment by Storage: a Statistical Overview. CRC for Catchments Hydrology Report, Melbourne, Australia.

Finney, B.A. and Middlebrooks, E.J. (1980) Facultative Waste Stabilization Pond Design. Journal of the Water Pollution Control Federation, 52 (1), 134-147.

Stockdale, A. (1991) Recent Trends in Urbanisation and Rural Population in Northern Ireland. Irish Geography, 24, 70-80.