Surface hydrology and hydraulic engineering
The ICGC works in the demarcation of floodable areas of the public water domain
The main lines of action in the field of floodability correspond to the delimitation of floodable areas for different return periods, zoning of the river space, proposing preventive and/or corrective measures to mitigate the effects, analysis of changes in floodability in the face of different future or projected planning alternatives, and raising awareness and informing the population of the risks of flooding.
Through this work, support is provided for territorial and urban planning, in order to comply with the Regulation of the Public Hydraulic Domain (DPH) (Decree 849/1986, of April 11).
The scope of application of this work is at the local (municipal and intermunicipal) and regional level, where the floodability of both permanent courses and minor courses with an ephemeral regime is studied.
● Local municipal studies, Municipal Urban Development Plans (POUM), sefocus on watercourses that flow through urban or urbanizable areas, areas in which it is estimated that possible urban growth could develop, or areas of special sensitivity.
● Local intermunicipal studies, Urban Master Plans (PDU), are developed on sections of watercourses that generally run through different municipal areas, in areas where the development of significant economic activity in the territory, of an industrial or service nature, is expected.
The ICGC has carried out 215 local flood risk studies, for the approval of POUMs, PDUs or other types of special or partial urban development plans.
In the field of regional flood planning, they are included within the scope of the project Planning of River Spaces of Catalonia (PEFCAT), during which the ICGC carried out the capture of information and processing of the Digital Terrain Model of 2,878 km of rivers, the tachymetric survey of 3,220 factory works, and the floodability study of around 1,300 km of rivers.
Flooding studies carried out at the local level (left figure) and at the regional level (right figure). Update date: August, 2017.
In achieving the different tasks, we work together and following the guidelines of the Catalan Water Agency (ACA) and the Ebro Hydrographic Confederation (CHE), as well as in collaboration with the General Directorate of Territorial Planning (DGOTU).
Examples of study areas. In the left photograph, detail of the upper section of the Noguera Ribagorçana (2008), and in the right photograph, detail of the Llobregat River, as it passes through Gironella (2006), during the work of the Planning of Fluvial Spaces of Catalonia (PEFCAT).
The tasks carried out in these studies are broadly as follows:
● Hydrological study consisting of determining the maximum flows or design hydrographs.
It is based on the analysis of information from the terrain in the basin or sub-basins of study; outcrop lithologies in the area, land uses and hydromorphometric characteristics of the basin or sub-basins (surface, slope, etc.), which determine the infiltration capacity of the land and, consequently, the surface runoff. The flows are obtained from the hydrological study to carry out the hydraulic modeling.
Hyetogram and calculation hydrograph obtained from the hydrological study
The cartography used corresponds to the cover map of the sun of Catalonia, at a scale of 1:5,000, from the Center for Ecological Research and Forestry Applications (CREAF), and the geological and geothematic cartography available at scales 1:50,000 and 1:25,000 from the ICGC (see catalog).
● One-dimensional (1D) or two-dimensional (2D) hydraulic modeling of river courses.
Hydraulic calculations study the drainage capacity of a river course, possible overflows and how the different volumes of water are distributed in different flood scenarios.
In urban areas, sufficiently detailed cartography is needed to define a quality terrain geometry for hydraulic calculations, which allows for the faithful representation of the variations in elevation of streets, drainage channels, and areas that act as an obstacle to flow. The extension must cover the entire area of the river courses and the flood plain.
A high-precision digital terrain model (DTM) is obtained from the ICGC, with a pixel size of 1x1 and 2x2 m, obtained using airborne laser altimetry technology (LIDAR).
Example of capture and processing of the digital terrain model, DTM and Lidar
Using the topography of the land obtained with Lidar technology, meshes are generated for hydraulic calculations that represent the 3D surface of the land, where artificial elements that may be significant to the flow advance (dams, walls, etc.) are subsequently incorporated, the 3D volumes of the buildings that are deemed necessary, as well as the hydraulic structures.
Example of a 3D grid used to represent terrain geometry in hydraulic calculations
● Zoning of the river space, based on the DPH Regulation.
From the hydraulic calculations, the corresponding coverages of the flood limits and their associated hazards are obtained, for the different return periods studied.
Finally, the zoning of the river space is drawn up, which consists of the delimitation of the public hydraulic domain, preferential flow zone, and flood zone for the 500-year flow; as well as the easement zone, which corresponds to the lands that remain within a width of 5m from the limit of the riverbed, and the police zone, which corresponds to a width of 100m from the limit of the riverbed.
Example of the delimitation of flood zones in an industrial estate in Baix Llobregat (left figure) and in a sector of Sant Carles de la Ràpita (right figure)
Example of the final zoning map of the fluvial space according to the DPH Regulation, area of the confluence of the Llobregat and Arija rivers
Another field of action corresponds to torrential hydraulics, for the hydraulic study in active basins and ravines in relation to the contribution of solid load, and the detection and inventory of fallout cones with recent activity, with the possibility of finding material susceptible to mobilization, or phenomena of erosion, undermining or deposition of material, in the face of heavy rain episodes.
Left photo, detail of the Rebaixader ravine, between the villages of Senet and Aneto; right photo, detail of the Tossal de la Mola ravine, in Pont de Suert.
Other lines of work refer to advice on the drainage capacity of drainage works and open or underground pipelines, in the implementation of new infrastructures and new urban developments.