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Structural Areal Measures (SAM) refer to spatially discrete interventions implemented over defined surface areas within the catchment. Unlike linear measures that operate along flow pathways, these measures occupy identifiable land units and are typically designed to retain, store or regulate water and associated nutrient fluxes.
Within the OPTAIN modelling framework, Structural Areal Measures were represented as spatial entities integrated into the hydrological model. Their effects were assessed through process-based simulations at field and catchment scales, and their contribution to performance indicators was analysed within the multi-objective optimisation framework.
Representative examples of Structural Areal Measures assessed in OPTAIN include:
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Retention ponds
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Micro-reservoirs
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Afforestation areas
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Conversion of arable land to forest
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Peatland management areas
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Designated controlled drainage zones
Retention ponds and micro-reservoirs are designed to temporarily store runoff and reduce peak flows, while also influencing sediment and nutrient retention. Afforestation and land conversion measures alter evapotranspiration, infiltration and long-term soil-water dynamics. Peatland management can affect water storage capacity and nutrient cycling depending on hydrological conditions.
Model-based results indicate that the effectiveness of Structural Areal Measures depends strongly on location, size and integration within the catchment system. Their impacts are often highly spatially variable and may require careful targeting to generate measurable improvements at catchment scale.
In optimisation analyses, these measures frequently contributed to improved performance when strategically combined with Land Management and Structural Linear Measures, forming diversified portfolios that balance water retention efficiency, nutrient retention efficiency, agricultural productivity and cost-related considerations.
As with all categories presented in this section, the reported outcomes represent simulation-based predictions derived from modelling and optimisation analyses, and do not reflect field implementation or monitoring activities.