Satellite-Based Monitoring to Manage Coastal Water Quality Risks under Climate Extremes

Coastal water quality is a critical management issue for the state of New South Wales (NSW), Australia, which has approximately 2,137 km of coastline supporting diverse ecosystems, recreational beaches, fisheries and coastal communities. Like coastal regionals globally, the NSW coast is increasingly exposed to climate extremes. These extremes intensify run off from catchments, rivers and estuaries, placing additional pressures on coastal and marine ecosystems. These pressures occur alongside other climate-driven impacts including coastal erosion, sea level rise, and rising sea temperatures, collectively increasing risks to environmental health, the economy and community wellbeing.

Funded by the Marine Estate Management Strategy, NSW DCCEEW partnered with CSIRO to map coastal outflows using Earth observation (EO) technologies. Applying decadal satellite imagery to map the extent and characteristics of plumes generated by major NSW river systems. a. According to NSW DCCEEW personnel, the project has delivered a "step change in capability", enabling consistent, large-scale characterisation of discharge properties across regional NSW catchments.

Satellite based monitoring provides synoptic spatial and temporal coverage required to observe coastal water quality responses to extreme rainfall and runoff events—a capability achieved through in-situ measurements alone. Repeated observations at regional scales allow patterns, trends and cumulative impacts to be detected and compared more systematically. This collaboration demonstrates how EO can meet a critical management need. It strengthens the evidence base for decision making and forms the foundation for future operational applications that improve preparedness for climate extremes. In addition to supporting long-term resilience of NSW’s marine estate, there is also a high potential for application in other coastal jurisdictions nationally.

Managing coastal water quality under a changing climate requires the ability to anticipate where and when poor water quality outcomes are likely to occur following significant rainfall. Catchments across NSW have different responses to extreme weather, influenced by land use, hydrology and connectivity to estuaries and the coast. Historically, decision making has relied on sporadic, localised or reactive sampling, often after impacts have already occurred.

This project addresses these challenges by using EO to reveal how different catchments respond to rainfall and runoff at scale. Satellite derived information enables NSW DCCEEW to identify which catchments are most vulnerable to elevated sediment loads following floods and intense rainfall, as well as where these impacts are most likely to affect estuaries, coral and rocky reefs, fisheries, habitats supporting marine mammals, reptiles, birds and recreational waters. The availability of this product is expected to continue to enable faster, more targeted and proportionate management responses following extreme weather events, supporting adaptive management approaches to mitigate similar impacts in the future.

The outputs currently support the delivery of the Marine Estate Management Strategy by informing the prioritisation of interventions, guiding direct catchment management actions and strengthening long-term planning. As the product moves towards operational use, it will also enhance NSW DCCEEW’s ability to work with local councils, regional partners and other stakeholders to address risks at their source—for example, by targeting land management improvements in high impact catchments where they will deliver the greatest benefit.

Building on the success of the initial phase, the next stage of the project will assess the exposure of marine parks across NSW to key environmental variables, including turbidity, chlorophyll concentration and sea surface temperature. By analysing these variables at the scale of entire marine parks—rather than focusing on individual sections of coastline—the work will enable a more comprehensive assessment of spatial patterns, cumulative pressures and environmental risk. This approach will improve understanding of which marine parks are exposed to water quality and climate-related stressors, support assessment of cumulative impacts, and directly inform the development and refinement of marine park management plans.

Through the Coastal Outflows Project, NSW DCCEEW partnered with CSIRO to apply EO science to address the knowledge gaps around sediment discharges from regional NSW catchments. This Coastal Outflows project integrates a decade of Landsat8 satellite imagery (2013 - 2022) with advanced deep-learning techniques to deliver a coastal outflows product for the region, specifically for NSW's Hunter, Hawkesbury and Clarence catchments. The application of EO imagery and science is reducing the knowledge gaps around sediment discharges from these areas (Figure1 (a)).

This approach links rainfall, land use and sediment runoff to observed changes in coastal water quality, enabling NSW DCCEEW officers to better understand how catchment processes influence the marine environment—particularly during and after climate driven extreme events. The resulting satellite derived products quantify TSS dynamics associated with runoff and flooding, providing actionable intelligence to support environmental planning, catchment management and risk assessment across NSW’s coastal regions.

Additional products derived from this project include:

Remote sensing water quality products include: TSS, DOC, Chl-a, CDOM specific absorption, the light diffuse coefficient within the water column (kd490), a range of Inherit Optical Properties (IOPs,) and per pixel optical closure.

Importantly, this is not a one-off research exercise. In the future it is hoped that this tool will be accessible through online platforms, and with predictive AI capability, there are opportunities to support early warning systems that would have increased benefits to aquaculture, tourism, local government and emergency services.

This study uses a combination of satellite observations, field measurements, and modelled hydrological data to understand how sediment-rich freshwater flows from catchments affect coastal waters.

Satellite imagery from Landsat-8 is the primary data source for observing coastal water quality. These images were analysed to estimate water turbidity, which is used as an indicator of Total Suspended Solids (TSS). The satellite data were processed using a machine learning model trained with in-situ water and spectral samples, which provide measured information on sediment concentrations and the optical properties of water. This ensures that satellite estimates are grounded in real world observations.

The satellite analysis was applied across coastal waters adjacent to the Hunter, Hawkesbury and Clarence catchments over the period 2013 to 2022, allowing changes in coastal outflows to be examined over time and across regions.

To understand what drives these coastal responses, the study also used outputs from the Australian Water Resources Assessment – Landscape (AWRA-L) model. This national hydrological dataset provides daily information on rainfall runoff, soil moisture and drainage across Australia. These data help link rainfall events and catchment conditions to observed sediment plumes in coastal waters.

A key outcome for NSW DCCEEW has been the ability to visualise TSS discharges across catchments using consistent, satellite-based evidence. This capability makes it possible to identify which catchment characteristics—such as land-use, connectivity and hydrological behaviour—amplify downstream water quality impacts. These insights, previously difficult to obtain at scale of the NSW coastline, now provides a strong evidence-base to support targeted actions to reduce water quality impacts.

By shifting from post-event observations to forward looking intelligence, the project has directly improved how water quality risks are managed in practice. NSW DCCEEW is now better positioned to take proactive, timely and proportionate action following extreme rainfall events and to plan more strategically for future climate extremes.

The value of this capability has also attracted interest from other key government partners, including the Department of Primary Industries and Regional Development (Fisheries) and Transport NSW (Planning). These agencies recognise that increased spatial and temporal information can directly support their objectives and deliver shared benefits across the State. For example:

The ability to observe, quantify and compare impacts across multiple catchments supports more integrated 'catchment-to-coast' planning, strengthening coordination across governments, local councils, regional natural resource managers and catchment authorities, and land-use planners. For example, evidence of downstream impacts can guide development controls, stormwater management and buffers in sensitive catchments, resulting in more resilient community assets, protected tourism areas and reduce clean-up and recovery costs following extreme events

Overall, this project, in its initial phase, has the potential to support a national shift in catchment to coastal considerations from the perspective of water quality. Increased temporal and spatial data, derived from satellite imagery has opened the door to a new way of approaching the management of coastal outflows, which have significant benefits for the communities around regional catchments through:

By enabling earlier, more targeted and more proportionate decisions, this work can help shift coastal and catchment management from reactive clean-up to risk reduction and resilience building.