Analyses of Low Impact Development Strategies using Continuous Fully-Distributed Groundwater and Surface Water Models
- 1. Analyses of Low Impact Development Strategies using Continuous Fully- Distributed Groundwater and Surface Water Models Presented by: February 22, 2012
- 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 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 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 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 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 PRMS: 2-Layer, Energy Balance Snow Pack Model Areal snow depletion curve created using MODIS data Conceptual model
- 8. 8 Need to Represent Local Detail: Distributed Input Data • Precipitation (NEXRAD) • Rainfall intensity • Min/Max temperature • Solar radiation • Potential evapotranspiration
- 9. 9 Need to Represent Local Detail: Terrain Analysis – High-resolution 10 m DEM
- 10. 10 Need to Represent Local Detail: Cascading Overland Flow Routing
- 11. 11 Need to Represent Local Detail: Cascading Overland Flow Accumulation & Routing
- 12. 12 Need to Represent Local Detail: Geology
- 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 Groundwater Discharge to Ecologically Sensitive Features: coldwater fish spawning reaches
- 15. 15 Groundwater Discharge to Streams: Reverse Particle Tracking
- 16. 16 Topographical controls on groundwater recharge Discharge received in roadside ditches an swales
- 17. 17 Cascading Overland Flow Routing: Feature-based water balances
- 18. 18 Cascading Overland Flow Routing: Feature-based water balances
- 19. 19 Cascading Overland Flow Routing: High recharge at geological boundaries
- 20. 20 Hydroperiod Animations: Florida Everglades Click for Animation
- 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 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 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 Low Impact Development Strategies Case Study: Seasonal soil moisture Click for Animation
- 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 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