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Natural Small Water Retention Measures (NSWRM) are land and water management measures designed to increase the capacity of landscapes to retain, regulate and reuse water and nutrients. In agricultural contexts, they influence hydrological processes such as infiltration, evapotranspiration, runoff generation and nutrient transport.

Within the OPTAIN project, NSWRM were analysed as modelled planning options integrated into process-based hydrological and nutrient transport models. Their effects were assessed through simulation rather than field implementation.

Purpose: NSWRM are primarily focused on enhancing the ability of small catchments and agricultural landscapes to retain water. This not only helps in managing water quantity by reducing runoff and increasing infiltration but also improves water quality by trapping sediments and nutrients. It includes:

Water Retention: Increasing the capacity of landscapes to hold water, thereby reducing the volume and speed of runoff.

Nutrient Management: Preventing the loss of nutrients through runoff and promoting their absorption and reuse within the landscape.

Flood Mitigation: Reducing the risk of flooding by slowing down water flow and increasing the landscape’s ability to absorb excess water.

Drought Mitigation: Enhancing the availability of water during dry periods by improving soil moisture retention and groundwater recharge.

Biodiversity Promotion: Creating and maintaining habitats that support a diverse range of flora and fauna.

Soil Health Improvement: Reducing soil erosion and improving soil structure and fertility.

The sponge functions of a landscape refer to its ability to soak up, store and slowly release water.

It is possible to distinguish 3 sponge functions:

1. Intercept rainfall where it falls and stimulate infiltration into the soil;

2. Slow down the runoff that has formed on the surface, is drained from groundwater, or is accumulated in streams;

3. Temporarily store excess water in the soil, groundwater or surface water bodies.

Sponge functions of a territory play the role of regulator of water. They lie at the heart of a complex system of interconnected physical processes, binding all actors and sectors together (see illustration scheme). The parameters within these sponge loops are numerous. We have become champions at monitoring them separately in every sector, while clearly seeing that they are intrinsically linked. If we organize ourselves to positively activate sponge loops, we unlock a chain reaction of benefits in favour of water availability, quality, safety, food production and biodiversity, all at once. 

Sponge functions are context-specific and must be evaluated for a myriad of different hydrometeorological events, ranging from annual floods and droughts to more extreme events. The greater the sponge functions in the landscape, the more rainwater can be stored and/or used by vegetation, and surface runoff slowed, thus reducing or avoiding flooding downstream. However, it is important to note that sponge functions are not unlimited. Once full, a sponge can no longer store water to reduce the impact of floods, and once empty, it can no longer provide water in the event of a drought, yet for more frequently occurring events, this approach will contribute to the reduction of impacts both in space and time. 

A biophysical parameter is a measurable characteristic that can help in defining a particular system. It can cover individual substances, groups of substances or be defined by its measurement method like turbidity or the mesurement of oxygen consumption like BOD5 or COD. It is generally expressed by a value and its unit.