Impact of Urbanization on Aquifer Recharge in Mexico City Basin

1. Impact of urbanization on the recharge of the aquifer system in the Mexico City basin. Mauricio Santillana April 28, 2005 CE 394 K2

2. Outline • Motivation. • Long term objective. • In class project objective. • Description of a land development model for the outskirts of Mexico City. • Coupling of a land development model with a hydrological model. • Observed tendencies

3. 1. Motivation Disordered and non-regulated urban growth in Mexico City represents a major problem that has led to degradation of both, natural and social environments. • Water aquifer recharge has been blocked. • Natural reserves have been urbanized. • High risk flooding regions are commonly populated. These problems have become a major concern in recent years.

4. 2. Long term objective: To couple an urban development model with a simple yearly model of the aquifer system in the south of Mexico City. 3. In class project objectives To find tendencies in water table changes in the aquifer with respect to urbanization using data acquired from monitoring wells in the Mexico City.

5. 4. The urban development model • The following model was designed to provide decision-making agencies with a suitable tool to generate probable scenarios of urban development based on a given set of hypothetical conditions. • The mathematical framework used to simulate this phenomenon emanates from the study of complex and self-organizing systems. The model is based on Cellular Automata.

6. 4. The urban development model The main attributes considered in the simulation are: • Closeness to road network (Connectivity) • Slope, topographic accidents. • Closeness to other human settlements. • Land Use (Rural, Forest)

7. 4. The urban development model

8. 4. The urban development model“Probable scenario generation”

9. 5. Coupling of a land development model with a hydrological model. New variable to be modeled: Infiltration and eventually recharge

10. 5. Coupling of a land development model with a hydrological model. • Once the urban model is calibrated, then the output is used as a dynamic input grid in a hydrological model where the relevant state variable is the infiltration. • This qualitative approach will allow specialists to evaluate their hypothesis about the environmental impact of urbanization

11. 6. Identified Tendencies:Water table measurementsfrom Kriging-Interpolated grids

12. 6. Hypothesis • The volume of water in the aquifer is directly proportional to the recharge (proportional to infiltration) which is inversely proportional to the impervious terrain (proportional to land development) in the recharge regions (??).

13. Limitations • Information in water resources in Mexico is limited and in many cases inexistent. • Estimations of runoff, evapotranspiration, rainfall, infiltration, water extraction, water consumption per capita, are being calculated. • A clear overexploitation of the groundwater in the city is taking place.

14. Thank you!Comments and Observations:mauricio@ices.utexas.edu

15. The model…(Cellular Automata) In order to build a suitable model, we first divide the domain of work in grid cells. These could correspond to pixels or sets of them, just like in a raster image. Each cell is in a state that depends on the information obtained from aerial photos and possesses attributes depending on its location.

16. Cellular Automata(States and transition rules)

17. 4. The urban model (Results) RealScenario 1995

18. 4. The urban model (Results) RealScenario 2002

19. 4. The urban model (Results) Output from Model 2002