A set of geomatics tools was developed to represent the impact of urbanization on runoff within distributed hydrological models.
The scientific objective was to investigate the behavior of territories undergoing gradual transformation.
The coupled approach enabled the study of two small peri-urban catchments in France and Chile, as well as the recharge conditions of the Dehesa aquifer (Chile).

Urban growth implies land use changes with natural and agricultural lands becoming urbanized. Distributed hydrological modelling of periurban basins requires an accurate spatial representation to take into account all these features and landscape changes. In this work we propose Geo-PUMMA, a set of GIS tools programmed in Python for GRASS that uses irregular meshes to explicitly represent the different components of the peri-urban terrain, particularly the elements affecting the flow paths (i.e. stormwater facilities, channels, streets and pipes). Geo-PUMMA gathers a series of geographical data treatment procedures which use spatial information maps (e.g. cadastral, soil types, geology and digital elevation models) to produce Hydrological Response Units (HRU) and Urban Hydrological Elements (UHEs) that make up a terrain representation more suitable for hydrologic modeling. Geo-Pumma was applied to 2 peri-urban catchments: the Mercier catchment (OTHU observatory, France) and the Estero El Guindo catchment (Chile). Geo-Pumma produces a terrain representation that is more representative of the actual drainage structure (Sanzana et al., 2017, 2018).
A coupled distributed hydrological model (WEAP) was also coupled with a groundwater model (MODFLOW) at the regional scale, to better assess the recharge to the groundwater of the Dehasa aquifer located in the Andean piedmont close to Santiago city. The model was calibrated using observations at the small experimental catchment scale (discharge) and at the regional scale (groundwater level) (Fig.1, Sanzana et al., 2019), showing the impact of inefficient irrigation of gardens on groundwater recharge.

Figure 1 : (a) monthly series for the calibration and validation periods, (b) correlations between monthly values for both calibration and validation periods, (c) flow duration curves, and (d) monthly average streamflows. (Sanzana et al., 2019)

Funding

Scholarship from CONICYT, bilateral ECOS-Sud project “Evaluation and Modeling of the Hydrological and Morphological Impacts of Urban Development in Peri-Urban Catchments,” and Irstea, which funded several research stays at Irstea.

Publications

• Sanzana, P., Gironás, J., Braud, I., Branger, F., Rodriguez, F., Vargas, X., Hitschfeld, N., Muñoz J.F., Vicuña S., Meijia, A., Jankowfsky, S., 2017. A GIS-based urban and peri-urban landscape representation toolbox for hydrological distributed modeling, Environmental Modelling & Software, 91, 168-185, http://dx.doi.org/10.1016/j.envsoft.2017.01.022
• Sanzana, P., Gironás, J., Braud, I., Hitschfeld, N., Branger, F., Rodriguez, F., Fuamba, M., Romero, J., Vargas, X., Muñoz J.F., Vicuña, S., Meija, A., 2019. Decomposition of 2D Polygons and their effect in hydrological models, Journal of Hydroinformatics, 21(1), 104-122, https://doi.org/10.2166/hydro.2018.031
• Sanzana, P., Gironás, J., Braud, I., Muñoz, J.-F., Vicuña, S., Reyes-Paecke, S., de la Barrera, F., Branger, F., Rodríguez, F., Vargas, X., Hitschfeld, N., Hormazábal, S., 2019. Impact of Urban Growth and High Residential Irrigation on Streamflow and Groundwater Levels in a Peri-Urban Semiarid Catchment. JAWRA Journal of the American Water Resources Association, 55(3): 720-739, https://doi.org/10.1111/1752-1688.12743