4 NBS potential in one sample neighbourhood: example of Saint Martin neighbourhood-Montpellier

Contexts in source publication

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... Lez river, which spring is the outlet of karst aquifer, is a small coastal Mediterranean river (29 km long -746 km 2 ) that crosses the city of Montpellier ( Fig. 14.1). The urban community of Montpellier (457,000 inhabitants) is characterized by the largest population growth in France and a rapid urbanization with massive soil-sealing (−2920 ha of agricultural and natural areas from 1990 to 2012). The Lez catchment is exposed to a typical Mediterranean weather marked by repeated droughts, heavy ...

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... results of the urban planning model provided land use maps for the three different urbanization strategies. We present in Fig. 14.3 a focus on one zone of the Lez Basin that shows differences of urbanization in the three strategies in the west of Montpellier. The figure especially shows the development of large patches of discontinuous urban housing (dense) around the peri-urban municipalities: Lavérune, Pignan, Saussan, Fabrègues, Saint Jean de Védas in the ...

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... of these solutions was evaluated based on photo interpretation of four sample neighbourhoods. The available space identified in the sample neighbourhoods was subsequently extrapolated to the whole urban areas of the watershed, considering the extent of the different types of neighbourhoods throughout the urban areas of the catchment (Fig. ...

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... the aquifer contributes to reducing the impact on flows and damage of the first rainfall event. However, once the karst is full, it no longer helps to reduce the flood. Therefore, from a statistical point of view, over a full hydrological year, active aquifer management has very little impact on floods and damage in the city of Montpellier (Fig. 14.5). Although differences can be observed between the three pumping strategies they remain very limited, especially to very high intensity rainfall (>50 mm/h) which are very ...

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... catastrophe loss risk model is composed of: the hazard unit, the vulnerability and damage units (Fig. ...

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... statistical analysis of predicted urban runoff with insured loss of residential homeowners provides the correlation between the runoff (expressed in m 3 /s) and the damage rate and between runoff and the destruction rate. These correlations are fitted in damage curves as illustrated in Fig. 14.7. Damages associated to a runoff below 0.07 m 3 /s are considered ...

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... impact is evaluated with predicted land use maps from the GIS model and associated infiltration coefficient obtained in the three strategies and the estimation of runoff hazard on the 2014 flood events. Figure 14.8 represents an example of hazard modeling for the laissez faire and the green strategies in the municipality of Cournonterral (periurban). ...

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... on avoided damage costs was estimated (Fig. 14.9) 2. A simple link between water retention resulting from GI strategies and the reduction of runoff was established by BRGM and used to estimate the impact of NBS strategies on the reduction of flood ...

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... Frejorgues Return period (years) 1H event (mm) 2H event (mm) 6H event (mm) 10 56 71 96 20 65 84 117 50 76 103 150 100 84 120 179 The relationship between runoff reduction and damage reduction is estimated in Fig. 14.9. The damages without NBS for different return period are also defined in Table 14.4. We identified the return-period of rainfall events based on the data of the Montpellier Frejorgues station. We obtain the following return periods in Table ...

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... also see a large heterogeneity of cost-effectiveness among the different individual NBS evaluated in the project (Fig. 14.10). This heterogeneity raises questions especially on the opportunity of integrating green roofs in future strategies considering their limited effect on water retention and their large ...

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... workshops with local stakeholders, in order to identify expected co-benefits, NBS implementation levels and potential barriers, and to introduce the In the main section of the questionnaire, the CE itself, respondent make choices between hypothetical flood management strategies for the Lez catchment presented in the form of choice cards (Fig. 14.11). In each choice card, respondents choose between two flood management strategies that achieve the same level of flood risk management but differ in the levels of implementation of NBS and in the level of contribution, in terms of tax increase. If neither of the two alternative is suitable for respondents, they can choose "Neither of ...

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... in year t, AD t is the Avoided Damage in year t, r is the discounting factor, 3 C t and OC t are implementations Costs and Opportunity Costs in year t and T is the time horizon of the assessment. We therefore obtain the following estimation of benefits and costs and economic indicators for the GI level 1 and 2 strategies (Table 14.10 and Fig. ...