Environmental Monitoring and Adaptive Management

Project Description

Exo Environmental have been working for the past year on the management of a maintenance dredging project, which has the added benefit of providing an opportunity to restore lost areas of saltmarsh. The harbour requires dredging to remove in excess of 100,000m³ of accumulated sediment, thereby clearing the navigation channels. The surrounding area, which is under the protection of several national and international designations, is recognised for saltmarsh and associated habitats. Yet many of the marshes are declining or in unfavourable condition, while coastal saltmarsh plays an important role in coastal defence and carbon sequestering. Given that the habitat is disappearing rapidly and is of such importance, the UK government has set targets to create new areas while achieving no net loss, therefore saltmarsh enhancement is a nationally important aspect of this project.

Dredging projects such as this can change the environmental quality, therefore monitoring was undertaken to establish an understanding of the baseline conditions and thence to assess environmental change and potential impact caused by the dredging works. Monitoring also allows for the assessment of compliance with permit, licence, legal and contract requirements and to help calibrate and validate the hydrographic model generated which will be used to predict the effects of the dredging activities.

The project has reached the end of the baseline monitoring stage, allowing a good understanding of the local environment and the measurement of chemical, physical and biological parameters, of water, sediment and ecology. Four stations were set up in the harbour area to measure tidal stream data and water quality, which collected data for 14 days at each location. Each station combined an Aquadopp® complete profiler system with an In-Situ TROLL 9500 multi-parameter water quality sonde.

A ‘van Veen’ grab sampler was used to collect samples of the sediment from the bed at five different locations to allow for bed material characterisation, following homogenisation of the sediment by the University of East Anglia laboratory. This information was used as input date for the bed friction as part of the hydrodynamic model.

Two water samples of a total of 10 litres each were taken from the harbour; each water sample was also measured with the turbidity sensor of the Troll 9500 sonde. The water samples were then analysed by the University of East Anglia Laboratory on solids per volume water, of these solids, organic and mineral particles were determined by volume by loss on ignition and the particle size distribution of the mineral fraction also measured. This allows us to understand the sediment balance and to correlate the turbidity measurements with suspended solids concentrations in mg/l.

Cohesive Strength Meter measurements were taken to provide information on the erodibility of sediment in relation to flow velocity, giving insight into areas of erosion or potential erosion. These were carried out at erosion thresholds of the intertidal deployment locations.

A Walz™ diving pulse amplitude modulated fluorimeter (PAM) was used to measure microalgal biomass. The PAM can be rapidly deployed and is non-destructive, allowing repeated measurement of treatment plots. These proxy measurements of biomass correlate well to EPS production and are therefore highly informative of the link between microalgal biomass and sediment biostabilisation via biogenic extracellular polymer production.

The receptors, or sensitive resources, which exist in the area, were identified, as well as the potential pathways between the dredging and the receptors. Also identified were the factors that the receptors are sensitive to and the critical thresholds for the receptors, as part of the baseline monitoring. The information on the potential effects on ecology is limited, so there is some uncertainty as to the potential impact of the dredging on sensitive receptors. Adaptive management can be used in an initial precautionary response as a way of dealing with this uncertainty.

We are now at the stage of having completed the baseline monitoring but yet to begin the dredging works, when surveillance and compliance monitoring will be undertaken. During surveillance monitoring , the baseline and during dredge conditions will be compared, providing the necessary information to assess the effect of the dredging activities on the local environment, as well as the efficacy of any mitigation and compensation measures. The feedback gained through surveillance monitoring may be used to alter the dredging design, as part of the adaptive management, to maintain environmental changes at an acceptable level.

Compliance monitoring will be carried out during and after the project to ascertain whether the activities comply with the mechanisms in place to protect environmental parameters; contractually and legally. This kind of monitoring may take place short – or long-term, depending on the time over which the local environment of the harbour reacts to and recovers from the changes caused by the dredging project. Monitoring schemes may be reduced, increased or modified according to the changes observed.

The need for monitoring combined with adaptive management of dredging projects is becoming increasingly more important for compliance. Exo Environmental is fully equipped and skilled to complete these projects successfully.

Project Details

  • AuthorWilliam Coulet
  • ClientBrightlingsea Harbour Commissioners
  • DateOctober 2015
  • CatergoryEcology