The efficiency of pond and constructed wetland (CW) treatment systems, is influenced by the internal hydrodynamics and mixing interactions between water and aquatic vegetation. In order to contribute to current knowledge of how emergent real vegetation affects solute mixing, and on what the shape and size effects are on the mixing characteristics, an understanding and quantification of those physical processes and interactions was evaluated. This paper presents results from tracer tests conducted during 2015-2016 in six full-scale systems in the UK under different flow regimes, operational depths, shapes and sizes, and in-/outlet configurations. The aim is to quantify the hydraulic performance and mixing characteristics of the treatment units, and to investigate the effect of size and shape on the mixing processes. Relative comparison of outlet configuration, inflow conditions, and internal features between the six different treatment units showed variations in residence times of up to a factor of 3. A key outcome of this study, demonstrated that the width is a more important dimension for the efficiency of the unit compared to the depth. Results underlined the importance of investigating hydrodynamics and physics of flow in full-size units to enhance treatment efficiency and predictions of water quality models.

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Abstract There is an increasing number of everyday flood incidents around the world, the impact of which poses a challenge to society, the economy and the environment. Under the Water Framework Directive (2000/60/EC), green infrastructure through the use of sustainable drainage systems (SuDS) is the recommended policy to manage and treat storm water runoff. Given the limited published experimental information on permeable interlocking concrete block pavements (PICPs), this paper presents novel results from an experimental laboratory study on a permeable interlocking concrete block pavement rig, investigating the short-term hydrology of the pavement, and water quality aspects related to the retention capacity of suspended solids (SS) through the pavement structure. Results of the volume analysis demonstrate high capability of the permeable structure to reduce the concentration time and attenuate the storm. Water quality testing was employed mainly as an indicator of the tendency of the suspended solids retention by the structure, indicating increasing tendency in the sediment mass retention progressively after each rainfall event. Experimental results obtained in the present study have direct application on the implementation of PICPs in car parking lots, urbanised pavement structures and pedestrianised walkways.