Hydraulics Efficiency of Constructed Wetlands and Ponds

Abstract

Constructed ponds and wetlands are widely used in urban design to serve a number of functions including stormwater management. The design of constructed wetlands for stormwater management involves a number of multi-disciplinary inputs. Fundamental to their sustainable operation are the proper control of the hydrologic regime of the wetland and optimal flow hydrodynamics within the wetland. Many ofthe problems encountered in constructed wetlands can be minimised or avoided by good engineering design principles. Poor wetland hydrodynamics are often identified as a major contributor to wetland management problems. Ponds and wetlands with a high hydraulic efficiency are expected to promote full utilisation ofthe available detention storage and near plug flow conditions. The shape and layout of urban ponds and wetlands are often varied to suit the landscape and to satisfy aesthetic requirements as an urban water feature. These can be achieved while maintaining an effective stormwater treatment outcome if steps are taken to ensure that the hydrodynamic behaviour of the system is not severely compromised. A consistent measure is required to allow the effects of design features to be evaluated against this criterion. This paper introduces a new measure for hydraulic efficiency that combines existing measures of flow uniformity and effective volume. Case studies are presented on the use of this measure to assess the effects of different pond and wetland shapes, locations of inlet and outlet, botanical layouts and basin morphology on the flow hydrodynamics.

How hydrological and hydraulic conditions affect performance of ponds

“…Persson et al (1999) raised this question and developed a hydraulic efficiency factor, Eq. (11), which can be used for comparing different designs.…”

“…The aim was to develop a method that linked hydraulic efficiency in both ponds and similar surface flow wetlands, to removal of nutrients and suspended solids (including heavy metals). This could then be used as a general method to compare and optimise pond layouts (Persson et al, 1999). The paper from the wetland conference was therefore further developed, and added to an investigation of how dispersion and effective volume ratio effects nitrogen removal according to the first-order kinetics model.…”

Uso de traçadores para avaliação da hidrodinâmica de sistemas alagados construídos operando sob condições climáticas tropicais

“…A eficiência hidráulica λ para as três unidades atingiu valores acima de 0,87. Segundo PERSSON et al (1999), wetlands com λ superior a 0,75 apresentam boa condição hidráulica, e valores inferiores a 0,50 denotam λ "pobre". Verifica-se que o tipo de corante utilizado no ensaio influencia, sobremaneira, os resultados dos parâmetros hidráulicos.…”

“…Os parâmetros tempo de residência experimental (τ R ) e número de dispersão (d) são decorrentes da centroide e da variância da distribuição, respectivamente. Já o parâmetro eficiência hidráulica (λ) foi calculado a partir do tempo no qual é detectado o pico de concentração do traçador e do tempo de residência nominal (PERSSON et al, 1999).…”

Modelling the fate of organic micropollutants in stormwater ponds

“…water volume varies due to dynamic storage and sediment thickness varies due to settling and resuspension) and the atmosphere is not included in the model. Different stormwater treatment units can be simulated by changing the number of serial tanks, which is defined to achieve a hydraulic efficiency λ (ratio between actual and theoretical hydraulic retention time (Persson et al, 1999)) resembling that of the real system under study. 189 190 191 192 193 194 195 196 197 198 The volume of the water compartment and the number of serial reactors were defined to represent the measured hydraulic behaviour of the Lilla Essingen pond.…”