Analysis of Groundwater/Surface Water Interaction at the Site Scale

Babcock Ranch Community Development Lee County, Florida

E.J. Wexler, P.J. Thompson G.F. Rawl, Dirk Kassenaar

IAH-CNC 2015

Waterloo, ON

November 4, 2015

Babcock Ranch Development

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Land purchased in 1914

Located on Florida west coast

Straddles Lee and Charlotte Counties

Babcock Ranch City to have 45,000 residents

First fully solar-powered city in U.S.

Location

West Coast of Florida

North of Ft. Myers.

Babcock Ranch Location

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Site located north of Caloosahatchee River near Ft. Meyers, FL

Telegraph Swamp is a key wetland feature

Sold to state in 2006 as a Nature Preserve

1100 km2 Study Area includes Babcock Ranch, Telegraph Swamp and subwatersheds to either side

Babcock Ranch

Model Boundary

Callosahatchee River

Telegraph Swamp

Conceptual Plan

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19,500 homes concentrated in “development pods”.

Four residential villages and five hamlets

Other light industry and commercial

50% of developed area to be left as nature reserve

Drainage Plan

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Runoff from developed areas directed to stormwater lakes

Overflow to wetland preserves

Some runoff directed to treatment marshes

Aggregate mines converted to larger stormwater lakes

Remaining discharge to streams going offsite

Seepage from stormwater lakes re-hydrates wetlands

Lee County Settlement Agreement

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Lee County concerned about wetlands and possible flooding in Telegraph and Trout Creek downstream of Babcock Ranch.

Wanted proof that stormwater management system will restore more “natural” (pre-settlement) conditions

Telegraph Creek

Modelling Approach

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Integrated model needed to simulate groundwater-fed wetlands and ET

Earthfx built an integrated GW/SW model for: “Current Conditions”

“Post-development” conditions - increased imperviousness and stormwater management

▪ “Natural Conditions” – all ditches, berms, mines, roads removed

Compare infiltration, storm flow, groundwater recharge, heads, and wetland hydroperiod under each scenario.

GSFLOW Code used for integrated Model

GSFLOW Code

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GSFLOW is a USGS code developed for integrated GW/SW modelling

Based on MODFLOW-NWT and PRMS (Precipitation-Runoff Modelling System)

Fully open-source, proven and very well documented ▪ PRMS submodel handles soil moisture

accounting and groundwater recharge

▪ Groundwater submodel provides water to soil zone in areas of shallow water table

Groundwater/surface interaction simulated for lakes and streams

PRMS Submodel in GSFLOW

Grid and Development Plan

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PRMS submodel was used as a distributed model

Calculates soil water balance for each 100 x 100 m cell.

Same grid used for MODFLOW submodel

Overland runoff routed between cells using cascading flow

Runoff can re-infiltrate downslope PRMS Submodel in GSFLOW

PRMS Submodel Parameters

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Four general categories: ▪ Topography

▪ Soil Properties

▪ Land Use/Vegetation

▪ Climate

Topography from LIDAR and USGS data ▪ Total elevation change: 55 ft

Soil properties from mapping ▪ % impervious, vegetation

type, CN values, cover density based on land use/cover mapping

Topography

PRMS Soil Mapping

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Grouped into 9 categories ▪ Mostly fine sand, but poorly

drained – B/D soils

▪ Muck/Organic soils in wetlands

High runoff during wet season (May-September) due to high water table

Better drained in dry season (October-April)

Soils

PRMS Land Cover

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FLUCS data

Natural cover is mainly wetland, upland forest, and rangeland

Agriculture is the primary land use ▪ Limited urban development

in south

Cover type modified for “post-development” and “natural” conditions

Land Use

PRMS Rainfall

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Rainfall shows wet-season/dry season variation

Rainfall also shows year-to-year variation

Averages about 1370 mm/yr

Annual Rainfall

Monthly Rainfall

NEXRAD

PRMS PET

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ET is very high year-round

Averages about 1323 mm/yr

Nearly matches average rainfall

Annual PET

Monthly PET

PRMS Results

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PRMS outputs daily values for Precipitation, Interception, ET, Hortonian and Dunnian runoff, fast/slow interflow, infiltration, and recharge

Easier to look at Monthly Averages

Daily Rainfall WY2006

PRMS Results

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November 2007 Rainfall August 2007 Rainfall

PRMS Results

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August 2007 Overland Runoff August 2007 Cascade Flow (in/mon)

PRMS Results

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August 2007 Infiltration August 2007 GW Recharge (after ET) - Current

PRMS Results

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August 2007 2007 GW Recharge - Natural

(Less RO, more ET)

August 2007 GW Recharge (after ET) – Post

(Less GW recharge due to impervious)

Groundwater Submodel

MODFLOW Calibration Targets

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13 significant streams

10 gages with 2-4 years continuous data

505 wetlands represented in current model

Structures at Curry Lake and Telegraph Swamp

All agricultural ditches and berms represented

Wells

MODFLOW Calibration Targets

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155 wells with water level data

Most are in surficial aquifer

All have 2-4 years of continuous data

Shallow wells in wetlands used as surrogates for wetland stage

Surface Water Features

Existing Structures

Post-Development Features

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130 Storm Water Ponds

130 Wetland Preserves

12 Treatment Marshes

121 Structures

Added code to GSFLOW to calculate stage/discharge for weirs, gates, and orifices

Surface Water Features

GSFLOW Submodel Results

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Groundwater model outputs daily values for heads, lake stage/volume, stream stage/discharge.

Data can be analyzed to determine hydroperiod.

Calibration can be done to average heads or to hydrographs

Daily Rainfall WY2006

GW Calibration

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Simulated average wet season heads versus observed

GSFLOW Streamflow Calibration Results

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Simulated (blue) and Observed (red) flows at three key gages

Daily Rainfall WY2006

JEI-570

JEI-567

JEI-569

Wetland Stage Calibration Results

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Simulated (blue) and Observed (red) stage at three key wetlands

JEI-509

JEI-1476

JEI-510

GSFLOW Results

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August 18, 2008 Streamflow August 19, 2008 Streamflow

GSFLOW Results

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Best seen as animation.

Shows rainfall, heads, streamflow, wetland and lake depth

Click for Animation

GSFLOW Results

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Detailed daily water budgets for each cell for all inflow/outflow components

Averaged for monthly and annual conditions

Averaged by basin and sub-basins

Results compared with natural and post-construction conditions

GSFLOW Results

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Simulated wetland hydroperiod

Ranges between 120-365 days

Blue areas are 365 days

Results compared with natural and post-construction conditions

GSFLOW Prediction Results

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Simulated flow under current and post-development conditions

JEI-570

JEI-567

JEI-569

GSFLOW Prediction Results

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Simulated wetland stage under current, natural, and post-development conditions – general improvement

Area 3

Area 1 (Curry Lake)

Area 2

Area 3

Area 1 (Curry Lake)

Area 2

Wetland Stage Hydrographs Natural, Post-development, and Current Conditions

GSFLOW Predictive Simulations

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Simulated 5-yr, 25-yr and 100 yr storm at JEI-570 - Improved

5 year Storm 25 year Storm 100-year Storm

Natural Post-Development Currrent

100-yr storm at JEI-570 under current, natural, and post-BRC conditions

Conclusions

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Integrated modelling is a powerful tool for evaluating natural and altered hydrologic response

With sufficient data, very good representations of the groundwater and surface water systems can be obtained

Integrated models can provide quantitative input to land development/storm water management studies

Questions?