Hydrological site assessment
The basis of any coastal ecosystem restoration or intervention
Nature pioneers already restoring with us
Understanding site hydrology
Hydrology, the movement and distribution of water, is one of the most critical factors in the establishment of coastal vegetation such as mangroves. Mapping and understanding site hydrology is the difference between guessing that plants establish themselves without being washed away, and a scientific action plan with quantified risks that can be mitigated. Financing coastal restoration projects doesn't need to be a gamble, future risks and scenarios can be modelled and quantified to improve confidence in returns.
We assess current site conditions and model future scenarios for coastal ecosystems, enabling the following.
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Understanding of current site conditions for mangrove restoration
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Quantified areas suitable for different local species establishment, based on current hydrological conditions - crucial to establish site viability
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Identification of erosion or sedimentation risks
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Quantified habitat conditions for local vegetation
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Identification of areas at risk from storm surges or nuisance flooding, with impacts on mangrove survival.
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Quantification of future risks and scenarios
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Sea level rise assessments
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Extreme weather impacts under different scenarios
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Intervention cost benefit (planting vs hydrological restoration)
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Project carbon permanence under different scenarios
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We do this in three steps, beginning with low cost remote sensing at regional scales, followed by calibration and validation through scientific field data from local teams, ultimately enabling high confidence predictive modelling to understand a site's future evolution.
Remote sensing
Example of inundation analysis results
The satellite/remote sensing forms the first step in our hydrological analysis, and can be conducted in the initial phases at low cost.
Using satellite data, we analyse time series satellite data and combine it with tide models to derive the following:
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Inundation period (percentage of time area is inundated), see example above.
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Tidal connectivity - indications that site inundation is correlated with the local tide, as a check on tidal flow and indicate areas where tide flow is blocked or restricted as in the example with fish ponds below
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Tide model correlation - Check that global tide models are appropriate at the site or if there are indications that this is an area where tide models are not reliable, crucial as a first step before estimating the risk profiles of storm surges and other tidally linked scenarios.
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Erosion/sedimentation - Check for indications of erosion or coastal accretion over the last 3 years, to highlight areas of risk and help estimate coastal dynamics as in the example below.
Tidal connectivity analysis highlighting restricted tidal flow
Erosion analysis highlighting erosion and sedimentation trends
This remote sensing analysis works best for open areas. When combined with local scientific data on species tolerated inundation ranges, it can inform planting or hydrological restoration interventions.
This analysis can be provided rapidly and at low cost, however all site decisions require the results to be validated with field measurements, and a thorough assessment of site viability is not possible with remote data alone. We offer either field work or training of local teams to collect scientific quality field data to augment the remote site analysis.
Field work
The full value of the remote sensing hydrological analysis is only unlocked when calibrated with field measurements. We can work directly on site to collect these measurements, and are also happy arrange the training of local teams to collect scientific quality hydrological data, improving long term operational capacity.
The most robust approach are high resolution LIDAR maps to capture the terrain under the canopy, which can be used to adapt the remote sensing inundation model to work under light canopy much more robustly. The LIDAR data also acts as ground truthing which can be used to estimate the uncertainty in the remote sensing analysis. We have months of field experience in collecting large LIDAR datasets with drones in mangrove ecosystems, and are also able to arrange training in LIDAR collection and drone flights.
With the under canopy topological data, the habitat ranges of local mangrove species can be scientifically quantified to inform site selection based on degraded areas inundation, and this data is also valuable for assessing local mangrove species mixes as a reference biodiversity benchmark for restoration sites.
For smaller sites, a lower cost alternative to LIDAR is the collection of survey grade GPS positions of the topology. We can train and lease out equipment to collect this, including the use of lower cost tools without needing a full RTK setup. This data also quantifies the remote sensing uncertainty and the zonation of wild mangroves, however with less confidence. The image below illustrates the rough mangrove zonation typical at many sites, and the difference in hydro period is always a significant factor in species selection that should be based on local measurements.
Critical for reliable risk modelling for projects is the measurement of local mean sea level at site, which is then used for sea level rise risk assessments and predictions of storm risk. For this, the best approach is to use local hydrological measurements of water levels using a tide logger with survey grade GPS positioning (to compare it directly with the remote sensing data, LIDAR DTMs or satellite based DTMs). We help to do this to an accuracy in the order of 10cm or better to robustly account for sea level rise and storm surge risks.
Example of approximate site zonation, specific site zonation should be assessed through a robust study
Modelling
The remote sensing and field work steps allow a thorough understanding of the current condition of a site, and can serve as a robust baseline for planning restoration interventions such as planting or hydrological restoration.
However, these ecosystems are highly dynamic and often significantly impacted by events outside the project bounds such as changes to river sediment flow (i.e. due to increased irrigation or dams upstream), weather events, sea level rise, and many other factors. These pose significant permanence risks to mangrove projects. Non permanence risk assessments are often a requirement under methodologies such as Verra and Isometric, necessary as part of the PDD and requiring a proposed mitigation strategy. As an example, 3 years of erosion resulting from a newly dug channel caused the loss of a large area of newly planted mangroves, historical mangroves and even local fish ponds, shown in the image below near a site we worked at in Java.
Evolution of a mangrove restoration site showing erosion removing the mangroves in the north, even causing the loss of fish ponds
Additionally, natural dynamics of these coastal ecosystems can allow low cost, high impact solutions such as channel digging or raising mounds to more robustly restore ecosystems over the long term, when these interventions align with local community needs such as waterway transportation and fishing.
For both risk analysis and intervention cost-benefit analysis, simulation and modelling of site hydrology and ecological change over time periods of 30 to 100 years is a critical tool. This is the next step of our hydrological offering and the most critical for understanding a project's risk profile. This predictive modeling removes guesswork, providing clear visibility into potential site outcomes rather than relying on hope for vegetation survival and permanence.
With the in depth hydrological modelling, we deliver a report with quantified uncertainties and risk modelling for various likely scenarios (such as sea level rise, extreme weather events, or coastal erosion) over a 30 to 100 year project time frame. This allows financing decisions shift from speculative bets to data-driven investments with quantified risk profiles and confident return estimates, and project developers can proactively monitor and mitigate key vulnerabilities.