Monitoring environmental parameters is crucial in all four phases of dredging – excavation, lifting, transportation, and disposal. These processes can significantly impact sedimentation and turbidity levels within a water body, leading to short-term environmental impacts. These impacts, such as increases in suspended materials, mixing and loosening of sediment layers, and the potential spread of contaminants, can have a profound effect on aquatic organisms and the ecosystem. It is, therefore, imperative that sediment is extracted during dredging using the most effective method to prevent or reduce these impacts.
Given the unique nature of each dredging project, your role in ensuring that different regulations are followed is crucial. These regulations, determined by environmental laws, site location, sediment properties, and local environmental agency guidelines, must be considered at all stages of dredging. Your responsibility to monitor turbidity and sediment processes before, during, and after dredging activities provides you with a comprehensive understanding of the water environment, enabling you to make informed operational decisions. Your actions can promptly identify any fluctuations in suspended materials, allowing you to respond effectively and ensure the health of the aquatic environment.
Turbidity and Dredging
Although many natural events influence turbidity levels, such as rainfall, river flows and hydrodynamic conditions, dredging is known to have a significant and immediate impact. Dredging activities cause turbidity levels to rise due to increased particles in suspension. Suspended sediment also directly stresses organisms by reducing the efficiency of their respiration processes. As aquatic organisms rely on sunlight, high turbidity levels can affect the food web by hindering photosynthetic processes, leading to plant and fauna mortality. Coral can be particularly vulnerable to changes in water clarity and increases in sediment. These areas must be protected during dredging. A reduction in water clarity can also affect the behaviour of aquatic organisms, as they are less likely to see their food, predators and mating partners, which can lead to a decrease in the species population within dredging areas. Monitoring turbidity is considered an essential part of dredging. Turbidity data can be used as a proxy for the total suspended sediment (TSS). Turbidity sensors have become a popular method of attaining TSS information. Alternatively, acoustic backscatter instruments can be used for suspended sediment profiling.
Measuring SSC
The suspended sediment concentration (SSC) in a body of water can affect the species and population of aquatic organisms inhabiting the area. SSC data can give information on dredge plumes, where the excavation, transportation, and deposition of sediment create clouds of particles. To reduce damage to the local ecosystems within these areas, SSC measurements can indicate if the amount of suspended solids has exceeded a certain level and is considered a threat to the ecosystem. With this knowledge, operators can respond.
Instrumentation
The AQUAlogger 310TY is a compact turbidity logger capable of monitoring turbidity, temperature and depth. The instrument is supplied with an SSC Converter, providing customers with a user-friendly method of converting turbidity readings to SSC. It can be deployed on a boat, mooring line, buoy or structure or integrated within a system. The instrument has standard real-time reporting capability, making it a suitable device for dredging applications.
The AQUAscat 1000 range is a series of high-frequency acoustic instruments that can observe profiles of SSC within a water column to provide information on sediment processes. Profiles can be observed at a single location to produce a time series, or transects can be taken to observe spatial variability, making the instruments ideal for dredge plume monitoring. Dredging operators can benefit from having more information on SSC fluctuations throughout all stages of dredging.
Monitoring before
Monitoring environmental parameters before dredging can give critical stakeholders a baseline knowledge of the water environment. This information is essential as it can be compared with the information attained during and after dredging. Using the AQUAlogger 310TY, the user can know the natural turbidity levels within the water body. This baseline of information will be critical in future data analysis. AQUAscat instruments are ideal for monitoring SSC before dredging operations take place, as they can provide information on the natural sediment processes that take place before dredging has been carried out.
Monitoring during
Immediate information is vital during dredging operations. A monitoring system that gives real-time data is considered the most effective way for operators to respond to substantial changes in turbidity or sediment. When levels of re-suspension increase beyond a certain point, operators can act immediately to prevent it from becoming an issue. With real-time reporting capability, operators can obtain immediate turbidity measurements. If water samples are taken before dredging, the user sets a conversion using the SSC Converter, allowing the logger to output SSC in real time.
Monitoring after
Monitoring the water after dredging activities can assess the water quality and determine any long-term effects. These results can be compared to the data taken before the dredging activities took place, allowing researchers to understand the environmental effects. This information is also useful for environmental agencies governing dredging activities.
A real-time system
The AQUAlogger 310TY can be integrated into a system to monitor turbidity and SSC. When monitoring turbidity for dredging, instruments can be stationed at multiple locations to understand the environmental processes better. Monitoring systems can be placed upstream to provide background data and downstream to show where the dredging is taking place so that operators can compare both data sets. The AQUAlogger 310TY can transmit the information to a laptop on deck or via a secure website to give real-time data. For the most efficient system, alarms can be integrated to notify dredging operators via email or SMS if turbidity has reached dangerous levels, which will allow dredging operators to respond promptly. Optical backscatter instruments give a single-point measurement, and therefore, a single instrument cannot provide information at multiple depths within a water column. One solution to this is to suspend sensors at various depths.