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DSD-INT 2019 Regional groundwater and geological voxel models for the Cauca Valley, Colombia - Zimmel

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Presentation by Geoff Zimmel, Deltares, at the iMOD - User Day, during Delft Software Days - Edition 2019. Tuesday, 12 November 2019, Delft.

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DSD-INT 2019 Regional groundwater and geological voxel models for the Cauca Valley, Colombia - Zimmel

  1. 1. i M O D U s e r D a y 2 0 1 9 – D S D - I N T 2 0 1 9 Regional groundwater and geological voxel models for the Cauca Valley, Colombia Geoff Zimmel
  2. 2. iMODUserDay2019–DSD-INT2019 2 Cauca River Valley • 3rd Iteration of a groundwater modelling program within the Cauca valley • Joint project between • CVC, IHE Delft, Deltares • Regional Groundwater Models • Better understand the hydrogeological system • Many stakeholders in the region with concerns about climate change altering groundwater availability • Voxel model • Phreatic aquifer protection • Groundwater Management Plan
  3. 3. iMODUserDay2019–DSD-INT2019 3
  4. 4. iMODUserDay2019–DSD-INT2019 4 Previous Work • ESCACES 1 & 2 • Hydrogeological model • Develop the understanding of river – groundwater interaction • Monitoring system • DAGMA • ESCACES 3 • All focused on water use and the effects of changing climatic conditions • Strategy development coupling technical and social workflows. ESCACES 1 ESCACES 2 ESCACES 3 PMAA Cali
  5. 5. iMODUserDay2019–DSD-INT2019 5 QuestionsClimate Change ScenariosVoxel ModelGroundwater ModelOverview
  6. 6. iMODUserDay2019–DSD-INT2019 6 Geology • Wellbore lithology data availability • Kh (dark) and Kv (light) shown on the right • Depth averaging within the hydrogeological unit to derive Keq values → transmissivity and vertical resistance values • Values consistent with previous model versions in the cental and south models A1 A2 B C 202 141 115 71
  7. 7. Groundwater Model • Head levels • Generally following the surface elevation. • Higher heads along the east and decreasing values entering the valley iMODUserDay2019–DSD-INT2019 7
  8. 8. Groundwater Model • Groundwater recharge areas • Flow direction between the A1 and A2 units • Recharge along in the highlands to the east and discharge onto the valley floor. iMODUserDay2019–DSD-INT2019 8
  9. 9. Groundwater Model • Flow lines • Forward flow lines • Starting points 1km x 1km spacing • Release point from the top of the phreatic aquifer iMODUserDay2019–DSD-INT2019 9
  10. 10. Groundwater Model • Flow lines • Reverse flow paths • Starting points ever 500m along the Cauca River • Release point from DEM elevation • Flow from the river to the recharge location iMODUserDay2019–DSD-INT2019 10
  11. 11. Groundwater Model • River Recharge / Discharge • Cauca River (Predominantly Gaining) • Most rivers have a combination of gaining and loosing sections • Only considers the portion in the boundary area iMODUserDay2019–DSD-INT2019 11
  12. 12. Groundwater Model • Problems • Poor observation well spacing for validation • Infrequent recordings only twice per year • Lack of drains under urban areas iMODUserDay2019–DSD-INT2019 12
  13. 13. Groundwater Model • Transient Model • Built to better understand the relationship between the wet and dry seasons • Difference between wet and dry seasons A1 (left) and A2 (right) • Negative – dry season levels higher then wet season • Positive – wet season levels higher then dry season levels iMODUserDay2019–DSD-INT2019 13
  14. 14. Groundwater Model • Transient • Positive values greater around pumping wells • Indication that there is pumping and drawdown during the dry season • Wet season and dry season are noticeable in time series taken close to the Cauca River iMODUserDay2019–DSD-INT2019 14
  15. 15. iMODUserDay2019–DSD-INT2019 15 QuestionsClimate Change ScenariosVoxel ModelGroundwater ModelOverview
  16. 16. Voxel Model • Purpose • Visualize the lithology distribution • Used and an input for a aquifer risk assessment • 500m x 500m grid size • Completed using iMOD XYZtoIDF batch function • 3 models were generated 1. (unsaturated) Between the surface and gwl (-5m) 2. (aquifer 1) Between gwl and a constant depth of 30m below DEM elevation 3. (aquifer 2) Between gwl and top of Layer B iMODUserDay2019–DSD-INT2019 16
  17. 17. Voxel Model • 3 models were generated 1. (unsaturated) Between the surface and gwl (-5m) • Voxel depth set at 0.5 meters • Cutoff originally set at gwl but 5 meters had to be added to deal with data loss issues. 2. (aquifer 1) Between gwl and a constant depth of 30m below DEM elevation • Voxel depth set at 10 meters 3. (aquifer 2) Between gwl and top of Layer B • Voxel depth set at 10 meters iMODUserDay2019–DSD-INT2019 17
  18. 18. Voxel Model • 3 models were generated 1. (unsaturated) Between the surface and gwl (-5m) • Voxel depth set at 0.5 meters • Cutoff originally set at gwl but 5 meters had to be added to deal with data loss issues. 2. (aquifer 1) Between gwl and a constant depth of 30m below DEM elevation • Voxel depth set at 10 meters 3. (aquifer 2) Between gwl and top of Layer B • Voxel depth set at 10 meters iMODUserDay2019–DSD-INT2019 18
  19. 19. iMODUserDay2019–DSD-INT2019 19 QuestionsClimate Change ScenariosVoxel ModelGroundwater ModelOverview
  20. 20. Climate Change Scenarios • 2 scenarios were identified • Baseline (2000 -2017 data) • RCP4.5 (Estimate recharge based on 2040 climate change predictions) • RCP4.5 data calculated from data gathered through downscaling of a global climate change model • 99 different recharge values were generated for each scenario, 198 new recharge scenarios in total • Each recharge value was then used as an input to groundwater models to estimate the effects on groundwater level of changing climatic (recharge) conditions • Head levels measured at five comparison points. • Differences between baseline and RCP4.5 models were generated at 10th, 50th and 90th percentile values. iMODUserDay2019–DSD-INT2019 20
  21. 21. Climate Change Scenarios • Slight changes can be seen throughout the valley but rarely exceeds +/- 0.5m on the valley floor • All 4 units see similar results and spatial variability and relationships • Average results from all 99 model runs are represented by p50 values • Low recharge represented by p10 and higher recharge by p90 iMODUserDay2019–DSD-INT2019 21 p10 p50 p90
  22. 22. Climate Change Scenarios iMODUserDay2019–DSD-INT2019 22 • Box plots including all 99 iterations for Baseline (Left) and RCP4.5(right) scenarios were calculated at each location • Mean values were compared to understand the potential effects of climate change as represented by the models • Overall the model results showed a low effect of climate change on groundwater levels for this area of interest given the model parameters
  23. 23. iMODUserDay2019–DSD-INT2019 23 Conclusions • Drawdown from pumping during the dry season has a much greater effect on local groundwater levels then climate change at a single point in time. But… • The cumulative effects of multiple dry years (due to climate change) could greatly reduce water availability in the valley • A strong water management plan is a crucial next step to proper resource management
  24. 24. iMODUserDay2019–DSD-INT2019 24 QuestionsClimate Change ScenariosVoxel ModelGroundwater ModelOverview

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