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Analyses of Low Impact Development Strategies using Continuous Fully-Distributed Groundwater and Surface Water Models

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Analyses of Low Impact Development Strategies using Continuous Fully-Distributed Groundwater and Surface Water Models

  1. 1. Analyses of Low Impact Development Strategies using Continuous Fully- Distributed Groundwater and Surface Water Models Presented by: February 22, 2012
  2. 2. 2 Earthfx Corporate Overview • Earth science data management and modelling company • The firm is staffed by programmers, hydrogeologists, hydrologists, and geological engineers who collectively offer modelling, programming, database and web technology expertise • over 50 years of combined ground water modelling experience • Ground water flow and contaminant transport modelling • Coupled groundwater/surface water interaction modelling • Geologic model construction • Geostatistical data analysis • 3-Dimensional data visualization • Software Products: • VIEWLOG Borehole GIS & WebServer • Sitefx Environmental Data Management System • Earthfx Data Model • Main office in Toronto Ontario, Canada.
  3. 3. 3 Problem Statement: A Collaborative Effort • SWMM – answers the questions about how Low Impact Development (LID) strategies affect end of pipe flows • Our challenge: • Do LID strategies really work? • Where do they work? • Geology, topography, depth to water table • How effective? • How much water can a LID strategy handle? • Which LID work best where • When – temporal questions?
  4. 4. 4 The Earthfx LID Approach • Case study: A planned development with an existing storm-water management model used to assess the effectiveness of storm water manage facilities in mitigating erosion in stream channels • Additional questions were raised on the impacts development would have to wetlands, streams, and groundwater resources • Earthfx was then brought in from a groundwater perspective, as we had a working groundwater model in the area • Our solution: GSFLOW • Fully-distributed, multi resolution, variable temporal resolution groundwater/surface water model • Full LID support • High resolution prevents the lumping of parameters over large areas and answers specific/local questions about LID function • Overland flow scheme provided a means to communicate hydrological processes to the existing erosion model
  5. 5. 5 GSFLOW: Coupled Ground-Water and Surface-Water Flow Model Based on the Integration of the Precipitation-Runoff Modeling System (PRMS) and the Modular Ground-Water Flow Model (MODFLOW-2005) • Initial release March, 2008 • Current version 1.1.4 (June 2011) • Maintained by the USGS • Open source (Fortran90/C) • Modular
  6. 6. 6 PRMS: Conceptual Diagram • Fully distributed • Continuous • Variable time step • Overland cascade flow routing • Stream flow routing (SFR2 package) • Green-Ampt, SCS CN, Empirical contributing area method • Unsaturated flow based- on 1D Richards equation • Can be run independently of MODFLOW
  7. 7. 7 PRMS: 2-Layer, Energy Balance Snow Pack Model Areal snow depletion curve created using MODIS data Conceptual model
  8. 8. 8 Need to Represent Local Detail: Distributed Input Data • Precipitation (NEXRAD) • Rainfall intensity • Min/Max temperature • Solar radiation • Potential evapotranspiration
  9. 9. 9 Need to Represent Local Detail: Terrain Analysis – High-resolution 10 m DEM
  10. 10. 10 Need to Represent Local Detail: Cascading Overland Flow Routing
  11. 11. 11 Need to Represent Local Detail: Cascading Overland Flow Accumulation & Routing
  12. 12. 12 Need to Represent Local Detail: Geology
  13. 13. 13 GSFLOW Outputs: • Hydrographs: all flow components (baseflow, unsaturated flow, direct runoff) • Streamflow: total flow routing, flow accumulation, groundwater discharge to streams and wetlands • Identifying high-volume recharge areas • Backward particle tracking from any feature • Topographic controls on recharge • Swales • Road ditches • High recharge at geological boundaries • Water table drawdown under land development • LID implementation vs No LID implementation • Feature-based waterbudgets and hydroperiod analysis • Animations
  14. 14. 14 Groundwater Discharge to Ecologically Sensitive Features: coldwater fish spawning reaches
  15. 15. 15 Groundwater Discharge to Streams: Reverse Particle Tracking
  16. 16. 16 Topographical controls on groundwater recharge Discharge received in roadside ditches an swales
  17. 17. 17 Cascading Overland Flow Routing: Feature-based water balances
  18. 18. 18 Cascading Overland Flow Routing: Feature-based water balances
  19. 19. 19 Cascading Overland Flow Routing: High recharge at geological boundaries
  20. 20. 20 Hydroperiod Animations: Florida Everglades Click for Animation
  21. 21. 21 Low Impact Development Strategies and Development Scenarios • Cell-based land use distribution can be utilized to assess alternate development plans (i.e., land use changes) • GSFLOW has the ability to account for the positioning of separate LID stores placed on a cell-by-cell basis • Feature based water budgets: e.g., groundwater vs. surface water component, hydroperiod, etc. • LID components used in GSFLOW are comparable to that of SWMM: • Surface Layer • Soil Layer • Storage Layer • Under drain/pervious redistribution • Pavement Layer* • Many LID strategies can be modelled: • Porous Pavement • Infiltration trenches and galleries • Rain Barrels and Cisterns • Green roofs • Downspout disconnect
  22. 22. 22 Low Impact Development Strategies A Case Study • Questions were raised whether there exists an impact to wetlands, streams, and groundwater resources due to the proposed development • Many LID strategies were applied: green roofs, downspout disconnect, pervious paving, bio-swales, infiltration gallery, and increase top soil depths • Preliminary analysis demonstrated that the existing development plans would lower the groundwater table 4.5m using a loosely-couple steady-state groundwater model • An infiltration gallery was used to attempt to mitigate this drawdown. • Simulated runoff from the GSFLOW model were easily applied to the existing storm water management model that was already in use to assess potential erosion and storm water management facilities
  23. 23. 23 Low Impact Development Strategies Case Study: Reduction in watertable drawdown from the implementation of LIDs BEFORE Development without mitigation AFTER Development with LID strategies
  24. 24. 24 Low Impact Development Strategies Case Study: Seasonal soil moisture Click for Animation
  25. 25. 25 Low Impact Development Strategies Case Study Results • Placement and effectiveness of infiltration gallery is highly dependent on geology and depth to water table • When compared with planned development without LID implementation, LID strategies demonstrated significant improvements: • reduced groundwater drawdowns by 86% • regained groundwater discharge to streams by 42%, and • reduced the increased runoff generated by 80%
  26. 26. 26 Conclusions and Future Directions • Potential exists for collaborative modelling efforts to provide a holistic solution for various stakeholders, able to answers questions such as: • Which LID strategies work, and how well? • Where does the positioning (and sizing) of LID mechanisms make them most efficient? • How does LID impact ecologically sensitive features and the sustainability of our water resources? • Site details are important, and they can be represented at high resolution • Limitless scenarios can bee applied • Impose land-use changes to elevation (need to modify topography) • Allowing for development to occur during a continuous simulation would provide for an impact assessment during the construction phase

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