AQUIFER

What an aquifer setting means

An aquifer changes the timescale of everything. Recharge enters over months, water moves through the formation over years, and the consequences of abstraction or of a change in land cover appear decades later and persist for decades after the cause is removed. A decision taken this year is still producing its effect when the people who took it have gone.

It also changes what the intervention is. The classical measures — retention, detention, floodplain reconnection — act on surface water. In an aquifer setting the interventions are about recharge: changing land use and cultivation so that more water infiltrates, managing runoff so that it reaches the aquifer rather than the drain, and controlling abstraction. Their effect is on groundwater levels, and through those levels on the wetlands, base flows, vegetation and dependent ecosystems that the aquifer sustains.

How it is assessed

Groundwater modelling is unavoidable, because the response cannot be inferred from surface measurements. The regional groundwater flow model establishes how the water body responds to changes in recharge and abstraction over the planning horizon, and it requires a geological model of the formation to be built first, since the flow model is only as good as its representation of the geometry and the properties of the layers.

The link to what people value runs through the ecosystems the groundwater sustains. The physical assessment of groundwater-dependent ecosystems and of groundwater-related ecosystem services establishes what the water level supports, which converts a change in head into a change in service delivered. That conversion is the step that makes a hydrogeological result usable in an economic assessment, and it is the contribution the project made to a problem that is usually left unresolved.

Characterization is particularly demanding for an aquifer, because it has to cover the surface catchment, the subsurface formation, the dependent ecosystems and the socio-economic uses of the water together, and it has to represent the recharge mechanism, which depends on both the geology and the land use above it.

Where it is used at NAIAD

Medina del Campo in Spain is the project's aquifer demonstration, a groundwater body under pressure from agricultural abstraction with dependent wetlands whose condition is the visible indicator of the water level. The 3D geological model, the regional flow model, the metamodel and the ecosystem service assessments were all developed or applied there, and they are the reference for the approach.