Diminution de la demande : jusqu'où et jusqu'à quand? L'exemple du département de la Gironde

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1 Diminution de la demande : jusqu'où et jusqu'à quand? L'exemple du département de la Gironde Declining water demand: how far and until when? The case of Gironde county Prévoir l'évolution de la demande en eau potable à long terme : enjeux, méthodes et pratiques en France et à l'international Séminaire BRGM AFB 14 décembre 2017

2 Le département de la Gironde The Gironde County Territoire : Km² Population : habitants Croissance démographique : +1,1% par an Territory : Km² Population : inhabitants Demographic growth: +1,1% per year 2

3 Qui prélève et pour quel usage? Who abstracts water for which uses? Eaux Superficial de surface water et nappes resources phréatiques and shallow aquifers Drinking water 3% Industry 27% Agriculture 70% Drinking water AEP 47% 47% Agriculture 47 % % Drinking water AEP 93% 93% Drinking water AEP 92% 92% Deep aquifers not in deficit Deep aquifers in equilibrium Overexploited deep aquifers The main objective of the water management plan (SAGE) is to sustain a water supply strategy based on GW which ensures low water price and the highest health security 3 water use per source (320 Mm 3 abstracted each year)

4 Long term forecasting is a necessity to manage deep Gironde aquifer Specific management constraints for deep GW in Gironde : Resources characterized by great inertia Long lifespan of drinking water infrastructures The hydrological state of aquifers depends on : Volumes abstracted; Spatial / temporal distribution of withdrawals => Need for mathematical GW simulation models Specify future abstraction level and location over several decades 4

5 Aquifer Management Plan (SAGE) Revised 18 juin 2013) STUDIES Diagnosis of resources(sept. 2010) Etat des lieux mise en œuvre (sept. 2010) Economic study (juil. 2011) Trends and scenarios(nov. 2011) Management objectives (mars 2012) Environmental study State decree PAGD (tome 1 et 2) et Règlement Plan setting: - Management objectives - Action priorities - Financial resources (all other plans must be compatible) Regulatory constraints enforceable againts third parties 5

6 Main directions of the Deep Gironde aquifer management plan GW abstraction should be reduced by: optimising water use through increased efficiency and reduction of use depending on all aquifers (priority) when this is not sufficient, alternative resources should be developed and substituted to overexploited aquifer Any substitution project should go along with a reduction of current GW abstraction licences:. 6

7 Total authorised abstraction (licences) Aquifer management pan: objectives and means Means listed in the plan 1. Revision of abstraction licences by the State 7 Volume currently pumped + - Sustainable pumping limit (volume) 2. Water efficiency policy 3. Development of substitution resources Who, where, with which financial resources? The plan objectives should be met with the che cumulated effect of water conservation measures and resource substitution

8 Les économies d'eau Volume pélevé en millions de m 3 Volume pélevé en millions de m ,5 12,1 10,6 10,6 69,1 67, ,5 22,2 =-10,3 Mm

9 Volume prélevé pour la prodcution Total abstraction: an indicator d'eau potable en m 3 Nb of inhabitants Nombre d'habitants Voume abstracted for drinking water supply (in m3)

10 Volume abstracted in m3 per inhabitant all ressources included Volume prélevé par habitant toutes ressources confondues pour la prodcution d'eau potable en m 3 /an/habitant Total abstraction: indicator and objective No water conservation Basic water conservation Reinforced water conservation Selecte assumptions for long term and large scale projections

11 Volume abstracted in m3 per inhabitant all ressources included Volume prélevé par habitant toutes ressources confondues pour la prodcution d'eau potable en m 3 /an/habitant Total abstraction: limits of water conservation policy? No water conservation Basic water conservation Reinforced water conservation 70?

12 Volume prélevé par habitant toutes ressources confondues pour la prodcution d'eau potable en m 3 /an/habitant What impact of climate change? impact of the 2003 heatwave Triggered thinking on the potential impact of CC on drinking water demand Statistical analysis of water demand dependency on weather conditions Analyse de la dépendance (Bordeaux Metropolitan area)

13 Lessons learnt from years 2003, 2007 and 2008 Volume / day Max daily temperature Demand react quickly to changes i maximum temperature Rainfall interact with Temerature: for a given t, demand increases twice less when it rains than when it doesn t; In Bordeaux Metropolitan area: If Tmax increases by +1 C => demand +1,6%

14 Volume abstracted in m3 per inhabitant all ressources included Volume prélevé par habitant toutes ressources confondues pour la prodcution d'eau potable en m 3 /an/habitant Total abstraction: What future evolution? No water conservation Basic water conservation Reinforced water conservation??

15 In brief What future water demand? Where will it take place? «where will settle the new inhabitants arriving each year?" This is difficult to predict as it depends on factors such as the relative price of land versus transportation costs (commuting):

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