CURRIDABAT Reconnecting the Rivers to the Urban Landscape Aerial Image of the Curridabat Cantón

A WATER SENSITIVE STRATEGY FOR THE SWEET CITY OF CURRIDABAT Reconnecting the Rivers to the Urban Landscape Aerial image of the Curridabat Cantón. Source Bing Maps A WATER SENSITIVE STRATEGY FOR THE SWEET CITY OF CURRIDABAT Reconnecting the Rivers to the Urban Landscape Author(s) Hans Gehrels Eskedar Gebremedhin Laurene Bouaziz Begoña Arellano Jaimerena A Water Sensitive Strategy for the Sweet City of Curridabat Reconnecting the Rivers to the Urban Landscape Client. Municipality of Curridabat, Costa Rica Contact. Irene María García Brenes Keywords. Water sensitive cities, urban flooding, bio-diversity, urban rivers, hydraulic modeling Document control Version 1 Date March 2020 Project n. 11201197 Pages 60 Status. Final Report Doc. version Author Reviewer Approver 1 J.C. Gehrels D. Meijer L.L.F. Janssen 4 Contents Executive summary 6 1. Introduction 8 1.1. Sweet City as a development model 9 1.2. Challenges and opportunities in Curridabat’s water management 12 1.3. Approach 14 2. Hydrology and geography of Curridabat 16 2.1. Introduction 16 2.2. River basins 17 2.3. Urbanization and land use 20 2.4. Hydrological catchment modeling 22 3. Hydraulic simulation of urban flooding 26 3.1. Introduction 26 3.2. Data preparation 26 3.3. D-Flow FM simulation results 29 3.4. Potential of enhancing infiltration and drainage 34 4. Conclusions on urban flooding 38 5. Recommendations for flood mitigation 40 5.1. Introduction 40 5.2. Recommendations for specific locations 44 5.3. General recommendations 56 References 59 5 A WATER SENSITIVE STRATEGY FOR THE SWEET CITY OF CURRIDABAT Executive summary map in Figure 5.3). Flooding from rainfall gener- ally showed higher maximum water depths and extents compared to fluvial flooding. In addi- The Municipal government of Curridabat (San tion, pluvial flooding caused significant flooded José Province, Costa Rica) aims to rehabilitate areas away from the main river beds. This is very biodiversity and to regenerate the natural riv- likely caused by malfunctioning of the drainage er system within the city. Deltares was invited system, either because of limited drainage ca- to support the city’s development of a master pacity or because of disconnections in the drain- plan on the future water management with a age lines. This interpretation was confirmed in comprehensive analysis of the water system of the field visits carried out during rain hours. Curridabat. Elements of particular importance are the rivers that connect the city with other Simulation of additional green infrastructure (for cities in the same river basin. This is based on flood prevention) and well-connected drainage the city’s vision entitled “Ciudad Dulce” which lines resulted in lower maximum water depths aims to increase biodiversity and quality of life and inundation areas compared to the initial in cities. model, confirming that urban flooding can be mitigated by increasing the amount of green in- A model-based analysis was conducted of the frastructure at the right locations and improving hydrological system of the territory of Curridabat the drainage system in terms of both capacity at two spatial scale levels: at the scale of the and connectedness. This served as a basis for river basins and the scale of the city. Two types exploring the potential of alternatives for the of flood mechanisms were considered: rainfall straightforward drainage of water from the city storm events leading to local flooding due to in- in terms of blue and green infrastructural inter- sufficient drainage capacity or bottlenecks in the ventions directed to delay, retain, and store wa- urban drainage system (pluvial flooding); and ter and hence mitigate urban flooding at specific heavy rainfall in the upstream catchment areas locations. leading to high river discharges and river bank overtopping in the city (fluvial flooding). The results from the identification of measures were then validated with a field inspection A hydrological model was set up for Curridabat’s carried out by Zamora Sauma et al. (2019). This river basins. The distributed hydrological model evaluation has been important to corroborate enabled to determine water quantities at any the flood simulations and to further specify pro- location within the model grid and to quantify posed actions. the water balance of the area. Simulated dis- charge time series were used as boundary condi- A first recommendation is to improve connec- tions for a hydraulic model of the water system tions and take out bottlenecks of the urban of the city. A hydraulic model was constructed storm water system. Specific locations were to simulate maximum water depths and flood identified with model simulations and described extent for fluvial, pluvial and combined (fluvial in the report. When improving drainage in this and pluvial) flood analysis. The hydraulic model way, it is important to consider the effect this was used to locate areas in Curridabat with high may have on the areas downstream of these probability of flooding and to identify locations bottlenecks. A second recommendation is to in- with flow obstructions (bottlenecks). The model crease infiltration of rainwater and delay runoff. predictions of flooding at 6 locations were val- Supported with additional information from idated with field inspections. The field inspec- the field inspection the report describes specific tions confirmed the predicted flooding at 5 out locations for implementation of retention and of 6 locations. infiltration projects. Thirdly, it is recommended that more space be provided for the river system. The impact of river flooding appeared to be most Although difficult to implement because of ex- significant along the Tiribí River and downstream propriation of strategic lands, specific locations of the confluences of the Puruses and María along the María Aguilar may be suitable for this. Aguilar, and Chagüite and Tiribí rivers (see the A final general recommendation is to invest in 6 FINAL REPORT rainfall and river gauging stations and in capacity building of professionals in Costa Rica in using simulation models such as developed in this study – to further support master-planning towards a water sensitive and biodiverse city. Open concrete ditch in the city 7 A WATER SENSITIVE STRATEGY FOR THE SWEET CITY OF CURRIDABAT 1. Introduction The Municipal government of Curridabat aims to rehabilitate biodiversity and to regenerate the natural system of multiple rivers within the city. Deltares was invited to support the city’s development of a master plan on the future water management for the Municipality of Curridabat with a joint comprehensive analysis of the water system of Curridabat. Curridabat is interested and inspired by recent work of Deltares on water sensitive urban design. Deltares incorporates the required capabilities with an initial understand- ing and recognition of Curridabat as a territory for future water-sensitive strategies. The purpose of this study is to contribute to the city’s master plan on the water management of the city of Curridabat. Elements of particular importance in Curridabat are the rivers that connect the city with other cities in the same river basin, the biodiversity, a sustainable water infrastructure, and social cohesion. A master plan for Cur- ridabat should therefore involve a water sensitive approach that is in line with the concept of a ‘Sweet City’ (as introduced in the next section) that is used as a development model in Currid- abat. It should also inspire neighboring cities to join Curridabat in a ‘Sweet River’ approach that extends to the scale of the entire river basin. In this study, a model-based analysis was conducted of the hydrological system of the territory of Curridabat, based on field observation, map- ping of local and open data, and interviews and discussions with local experts and stakeholders. A hydrological analysis at two spatial scales was carried out: at the scale of the river basins and at the scale of the city. This served as a basis for the development of recommendations for infrastructural blue and green interventions to mitigate urban flooding. In the next sections, the vision of the city is introduced, the water-related challenges and opportunities are discussed, and the approach followed is explained. 8 FINAL REPORT 1.1. Sweet City as a development model The local government in Curridabat has developed a vision entitled “Ciudad Dulce” which aims to increase biodiversity and quality of life in cities. An important element of the vision is to bring back the most important pollinizer, the native bee, as a member of the community (Image 1.1). The objective of “Ciudad Dulce” is to establish nature conservation as an urban ac- tivity to create a more bio-diverse, comfortable, Image 1.1: Bee hotel pollinator station in a park in Cur- clean, calm, colorful and better organized urban ridabat. environment (Image 1.2). + + + Polinizers+ Citizens& Vulnerable groups+ Pets ’ S Figure 1.1: Development vision of the Curridabat Cantón. Source: Guia de Plantas Dulces, Municipalidad de Currid- abat 9 A WATER SENSITIVE STRATEGY FOR THE SWEET CITY OF CURRIDABAT The vision of a Sweet City differs from tradition- Essential in this vision is a harmonious devel- al urban planning and urban design models. opment that uses biodiversity

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