Assessment of saltwater intrusion vulnerability in the coastal aquifers of Ninh Thuan province in the context of climate change

Transcription

1 Assessment of saltwater intrusion vulnerability in the coastal aquifers of Ninh Thuan province in the context of climate change T.T.Thoang, P.Q.Nhan,N.B.Hoang Page 1

2 OUTLINES 1. Introduction 2. Methodology 3. Results 4. Conclusion remarks Page 2

3 Introduction Fresh water is essential for humankind. But in coastal area, seawater intrusion is causing this precious resource to decline in quantity and quality. Focus on using the GALDIT method, this study aim to map the salt water intrusion vulnerability for coastal aquifers of Ninh Thuan province. Page 3

4 Introduction About Ninh Thuan Ninh Thuan is located in the south central coast of Viet Nam with Total area of 1558 km 2. Tropical monsoon climate typical of hot, dry, windy, strong evaporation Ninh Thuan province is the most arid region of Vietnam. Page 4

5 Introduction Hydrogeological condition The study focus on Coastal Quaternary aquifers of Ninh Thuan province including Holocen aquifer (qh) and Pleistocen aquifer (qp) The qh aquifer has an average thickness of 4.44m ranging from 0.5m to 9.94m. Formed by Q và Q 23 sediments. The qp aquifer has an average thickness of 7.07m ranging from 0.4m to 43.5m. Formed by mq and Q 13 sediments Page 5

6 Introduction Saltwater intrusion Salinity zone is mainly contributed in lower part Phan Rang plain. Total salinity area of Holocene aquifer is around 435.5km 2 (62,5% out of aquifer distribution). Total salinity area of Pleistocene aquifer is around 514.5km 2 (61.66% out of aquifer distribution) Page 6

7 Methodology Six factors of GALDIT method + G - (Groundwater Occurrence or Aquifer Type) + A - (Aquifer Hydraulic Conductivity) + L - (Height of Groundwater Level above Sea Level) + D - (Distance from the Shore) + I - (Impact of existing status of Sea Water Intrusion); + T - (Thickness of Aquifer) Page 7

8 Methodology Workflow of the study Page 8

9 Methodology Data collection Data was collected from many sources, hydrogeological mapping project, previous study on groundwater resourses, mainly from household digwells and boreholes field data. G: From hydrogeological map of Ninh Thuan scale 1: A: Holocene aquifer (vary from 0.15 to 5.15 m/day), Pleistocene aquifer (vary from 0.17 to 4.79 m/day). L: Holocene aquifer (vary from to m), Pleistocene aquifer (vary form -8.9 to m). D: From topography map of Ninh Thuan. I: Holocene aquifer (vary from 0.1 to 2.5), Pleistocene aquifer (vary from 0.06 to 2.28). T: Holocene aquifer (vary from 0.22 to 12 m), Pleistocene aquifer (vary from 0.3 to 25.8m). Page 9

10 Methodology Filtering, sorting, translating Filtering, sorting: The data vary from 2007 to 2011 and was collected from many sources, filtering and sorting is necessary to compute the vulnerability. Translating: The data for these factors mostly stored in excel spreadsheets and Mapinfo tab need to translate to shp file in order to compute in ARCGIS. Page 10

11 Methodology Factors developing and modifying GALDIT weights and indicator important rating modified based on Chachadi A.G. & Lobo Ferreira, J.P. (2001) Factor Groundwater occurrence / aquifer type (G) Aquifer hydraulic conductivity (A) m/day Height of groundwater level above mean sea level (L) m Weight Indicator Confined Unconfined Leaky variables confined bounded High Medium Low Very Very High Medium Low low low > <1 < >4 Important rating Factor Distance to the shore (D) km Impact of the existing status of seawater intrusion (I) Thickness of the aquifer (saturated) (T) m Weight Very Very small Small Medium Far High Medium Low Indicator low High Medium Low variables < >15 > <1 > <5 Very low Important rating Page 11

12 Methodology: Factors developing and modifying GALDIT vulnerability formula GALDIT = (1*G + 3*A + 4*L + 4*D + 1*I + 2*T)/15 GALDIT vulnerability class Vulnerability class high >=7.5 medium low <5 Page 12

13 Methodology Mapping The seawater intrusion vulnerability maps was constructed for each factor. and then a final seawater intrusion vulnerability map based the on combination all factors was using in Arcmap and Mapinfo. Page 13

14 Results Seawater intrusion Vulnerability map for Groundwater occurrence parameter of Holocene aquifer (left) and Pleistocene aquifer (right) Page 14

15 Results (cont ) Seawater intrusion Vulnerability map for Hydraulic conductivity parameter) of Holocene aquifer (left) and Pleistocene aquifer (right) Page 15

16 Results (cont ) Seawater intrusion Vulnerability map for Height of groundwater level above mean sea level paramester of Holocene aquifer (left) and Pleistocene aquifer (right) Page 16

17 Results (cont ) Seawater intrusion Vulnerability map for the Distance from the shore parameter Page 17

18 Results (cont ) Seawater intrusion Vulnerability map for the Impact of the existing status of seawater intrusion parameter of Holocene aquifer (left) and Pleistocene aquifer (right) Page 18

19 Results (cont ) Seawater intrusion Vulnerability map for Aquifer thickess, saturated parameter of Holocene aquifer (left) and Pleistocene aquifer (right) Page 19

20 Results (cont ) Final Seawater intrusion Vulnerability map of Holocene aquifer (left) and Pleistocene aquifer (right) Page 20

21 Conclusion remarks Groundwater in coastal aquifers of Ninh Thuan is now facing with seawater intrusion with more than 60% of the salinity zone out of the aquifer distribution. As seawater intrusion became the biggest concern for the groundwater resources of the province, it is necessary to evaluate the saltwater intrusion vulnerability in aquifers for planning and sustainable exploitation of groundwater in this province. Six factors in GALDIT method incorporated allow us to assess, numerically rank and map areas from low to high vulnerability. Page 21

22 Conclusion remarks The data was used for this study is lacking in many area. Groundwater level, water samples mostly collected in dry season. Interpolation was used for complement of the missing data. For more precisely vulnerability map, more data is required. The weight of each GALDIT factor was used the same as applied in other regions in the world, but considered for the condition of Ninh Thuan province that is limitation of this study and will be improved in further study Page 22

23 THANK YOU! Page 23