Hydrological and Flood Risk Study

What the hydrological or flood risk study is

The hydrological or flood risk study analyses the hydraulic behaviour of a catchment or river reach to determine the flood-prone areas for floods of different return periods, and to assess whether a project is located in a flood-risk area or may alter the surrounding hydrological regime. It is a study increasingly required by the Spanish River Basin Authorities (Confederaciones Hidrográficas) and by land-use planning regulation for projects near watercourses.

When it is necessary

• Projects located in a watercourse's policing zone (100 metres) where the River Basin Authority requires evidence that flood risk is not increased.
• Renewable-energy installations or infrastructure near areas identified as flood-prone in the hazard maps of the Flood Risk Management Plan (PGRI).
• Projects that significantly alter a catchment's surface runoff (sealing of large areas, significant earthworks).
• Urban developments that must evidence the absence of flood risk under land-use planning regulation.

Methodology

1. Hydrological analysis: calculation of flood flows for different return periods (T=10, 100, 500 years) using hydrometeorological methods.
2. Hydraulic modelling of the affected river reach, using specialised software (HEC-RAS or other validated tools), obtaining the flood extents for each return period.
3. Delimitation of the flood-prone area and the preferential flow zone under the Spanish Public Water Domain Regulation.
4. Assessment of the project's effect on the flood regime, verifying that it does not increase risk upstream or downstream.
5. Proposal of measures where an effect is detected: raising the elevation of the installations, sizing of cross drainage works, compensatory attenuation measures.

Common mistakes

• Using generic hydrological data instead of flow or rainfall series specific to the project's catchment.
• Failing to consider the cumulative effect of other nearby installations or developments that also alter the catchment's runoff.
• Modelling only the affected river reach without considering the hydraulic behaviour upstream and downstream of the project area.
• Not coordinating the hydrological study with the Public Water Domain occupation permit when both procedures are needed.

Why choose Ideas Medioambientales

We carry out hydrological and flood risk studies with HEC-RAS modelling for renewable-energy and infrastructure projects across the whole of Spain, coordinating the analysis with the Public Water Domain occupation permit and with the rest of the project's environmental documentation. Our in-house multidisciplinary team, with more than 25 years of experience and ISO 9001, 14001 and 45001 certification, works across the whole of Spain from our offices in Albacete and Madrid.

Tell us your project's location relative to nearby watercourses and we will tell you whether you need a hydrological study and what scope it should have.