Analyses of Low Impact Development Strategies using Continuous Fully-

Distributed Groundwater and Surface Water Models

Presented by:

February 22, 2012

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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.

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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?

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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

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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

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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

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PRMS: 2-Layer, Energy Balance Snow Pack Model

Areal snow depletion curve created using MODIS data

Conceptual model

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Need to Represent Local Detail: Distributed Input Data

• Precipitation (NEXRAD) • Rainfall intensity • Min/Max temperature • Solar radiation • Potential evapotranspiration

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Need to Represent Local Detail: Terrain Analysis – High-resolution 10 m DEM

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Need to Represent Local Detail: Cascading Overland Flow Routing

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Need to Represent Local Detail: Cascading Overland Flow Accumulation & Routing

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Need to Represent Local Detail: Geology

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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

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Groundwater Discharge to Ecologically Sensitive Features: coldwater fish spawning reaches

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Groundwater Discharge to Streams: Reverse Particle Tracking

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Topographical controls on groundwater recharge Discharge received in roadside ditches an swales

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Cascading Overland Flow Routing: Feature-based water balances

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Cascading Overland Flow Routing: Feature-based water balances

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Cascading Overland Flow Routing: High recharge at geological boundaries

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Hydroperiod Animations: Florida Everglades Click for Animation

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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

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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

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Low Impact Development Strategies Case Study: Reduction in watertable drawdown from the implementation of LIDs

BEFORE Development without mitigation

AFTER Development with LID strategies

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Low Impact Development Strategies Case Study: Seasonal soil moisture Click for Animation

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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%

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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