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Integrated Surface Water and Groundwater Interaction Modelling using

GSFLOW

Watertech 2012

Dirk Kassenaar Earthfx Inc.

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Presentation Overview

► Integrated GW/SW Modelling

It’s not as simple as you think is it

When is it needed?

► GSFLOW Overview

Model design by committee: who won..

► GSFLOW capabilities - illustrated through applications

Water budgeting and permit allocation:

► GW/stream linkage, total flow routing

Eco-hydrology, wetlands, lakes and reservoirs

► GW interaction with lakes and wetlands, reservoir control structures

Land use change and Low Impact Development

► Hydrology, soil and overland flow processes details

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Do you dream in polygons, lines or cells?

Polygons and HRUs: You’re a catchment hydrologist

Lines and Sections: You’re a hydraulic engineer

Cells and Layers: You’re a born groundwater modeller

Integrated Modelling= How do we move water between these geometric shapes??

GW/SW/SW modelling?

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SW and GW Model Representation ► Catchment Modelling (Hydrology):

Basic unit: Hydraulic Response Unit or HRU

Calibration focus: Flow at a gauge

Strong: Simulation of climate, soil processes and storage reservoirs

Weak: GW represented as a bucket with a decay term

► Hydraulic Modelling:

Basic unit: 1-D channel reach and section

Calibration focus: River level stage (flood levels)

Strong: Flood wave and peak flows

Weak: GW?? (too slow to consider) Climate?

► Groundwater Modelling:

Basic unit: Layers of interconnected cells

Calibration focus: GW levels

Strong: 3D distributed detail and levels

Weak: inflows/outflows (recharge??, baseflow separation??)

► Integrated Modelling: Both Flows and Levels

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Model Zones

S o i l w a t e r

U n s a t u r a t e d

z o n e P r e c i p i t a t i o n

E v a p o t r a n s p i r a t i o n

S t r e a m S t r e a m

E v a p o r a t i o n

P r e c i p i t a t i o n

I n f i l t r a t i o n

G r a v i t y d r a i n a g e

R e c h a r g e

G r o u n d - w a t e r f l o w

Zone of aeration

Zone of saturation

Soil-zone base

Zone 1: Hydrology (Vegetation, Snow and Soil)

Zone 2: Hydraulics (River Channels,

Wetlands and Lakes)

Zone 3: Groundwater (Unsaturated and Saturated aquifer layers)

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3 2

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When is Integrated Modelling NOT Necessary?

► Hydrology: Small catchments with limited GW

Poor aquifers: Little chance of cross-basin flows, limited losses to GW

Flashy catchments/run-off dominated systems

► Hydraulics: Peak flow, storm and flood modelling

Time frame in minutes: Will that peak flow take out the bridge?

► Groundwater:

Long term transient or steady state issues

Short term pumping test analysis (no recharge events)

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When is Integrated Modelling REALLY Necessary?

► Whenever there is significant movement of water between the zones: Hydrology (soil), Hydraulics (channel), GW (aquifer)

Significant individual or cumulative stress in one zone such that water may move between zones

Time frame of days to years

When detail is necessary (sub-catchment or site level)

When SW and GW watersheds diverge

► Typical integrated model applications Water budgeting, cumulative impact, permit allocation, drought impact

De-watering, mine pit re-filling, tailings pond analysis

Eco-Hydrology, wetland and fisheries impact assessment, low flow analysis

Land use change, land development

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Ideal Integrated Model

► Distributed, cell based, detailed where needed to represent engineering issues and stresses

► Physically based processes, but, more important, processes that match the scale, resolution and available data

Larger than the pore scale, but smaller than a lumped catchment

► Strong representation of the geometry and processes that interconnect the systems

Clear and direct interconnection

Capability to represent shallow subsurface layer geometry

► Calibration emphasis on measureable flows and levels

Precipitation, GW Levels, total stream flow at the gauge

► Simulation processes and time steps that represent real world stresses

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USGS-GSFLOW

S o i l w a t e r

U n s a t u r a t e d

z o n e P r e c i p i t a t i o n

E v a p o t r a n s p i r a t i o n

S t r e a m S t r e a m

E v a p o r a t i o n

P r e c i p i t a t i o n

I n f i l t r a t i o n

G r a v i t y d r a i n a g e

R e c h a r g e

G r o u n d - w a t e r f l o w

Zone 1: Hydrology (PRMS)

Zone 2: Hydraulics (MODFLOW SFR2 and

Lake7)

Zone 3: Groundwater (MODFLOW-NWT)

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► GSFLOW is a new USGS integrated GW+SW model Based on MODFLOW-NWT and USGS PRMS (Prepitation-Runoff Modelling System)

Both models fully open source, proven and very well documented

► GSFLOW Model Integration- design by expert committee: First author is a SW modeller, but there is strong evidence that the GW modellers

were quite persuasive (2 of the 3 zones are based on MODFLOW)…

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GSFLOW Hydrogeology:

MODFLOW-NWT (aka MODFLOW-2011)

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GSFLOW Hydrogeology

► Based on MODFLOW-NWT (MODFLOW-2011)

New Newton-Raphson matrix solver – all new engine

Designed for complex variably saturated and topographically complex systems

Designed for wet/dry converting layers

► ie. The shallow subsurface where GW and SW interact

Uses variable cell size MODFLOW FD grid

► GW Inflows: GW Recharge (PRMS discharge to Unsaturated Zone Flow package)

Either 1-D Richard’s equation or simple plug flow

► Selectable on a cell by cell basis within the model

► Very fast – use allows advanced UZF to be simulated only where necessary

► GW Outflows: New discharge processes supported:

Groundwater discharge (including ET) to the soil zone (and subsequent interflow)

Groundwater discharge to streams, lakes and wetlands using the SFR2 package

Unsaturated

zone

Ground-water flow

Evapotranspiration

StreamStream

Gravity drainage

RechargeWater tableWater table

Ground-water flow

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GSFLOW Dual-Grid Design

► GSFLOW can use two different grids for the SW and GW processes

► GW Mesh:

Uniform or variable cell sized MODFLOW-style grids

Allows refinement around the wells or significant geologic features

Used for aquifer layers, lakes and wetlands

► SW Mesh:

Polygon catchments (to keep the hydrologists happy), or, uniform or variable cell sized MODFLOW grids

► Benefit: Add cells and resolution only where needed

High resolution DEM for surface processes, runoff and focused recharge.

Use variable cell GW mesh for refinement around well, drawdown prediction,

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GW Feedback: Dunnian Runoff

► Runoff that occurs off fully saturated soils

Occurs when the water table is at or near surface

Not sensitive to surficial material K

► Can create runoff from saturated gravels

Spatially controlled:

► Tends to occur in stream valley areas

Seasonally controlled:

► Tends to occur in spring when water table is higher

► Not sensitive to rainfall intensity or model time step

U n s a t u r a t e d z o n e

S t r e a m S t r e a m

G r a v i t y d r a i n a g e

R e c h a r g e

G r o u n d - w a t e r f l o w

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Dunnian Runoff ► Likely occurs where depth to water table is less than 2 m

Stream valleys and slopes where flowing wells, springs and headwater seeps are present

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GSFLOW HydroG Conclusions

► Limits: Yes, it is still MODFLOW

But… not the MODFLOW that your father used

GSFLOW does build on the extensive industry knowledge of MODFLOW

► MODFLOW portion of GSFLOW can be run independently

► First GSFLOW time step is simply a MODFLOW Steady State simulation

► GSFLOW GW features:

New solver designed for complex shallow geometry and wet/dry layers

► Ideal for rewetting problems such as mine filling

Variable cell-sized GW mesh can be defined independently of the SW mesh

New processes: GW discharge to soil zone (and interflow)

► Benefit: High resolution representation of

Full simulation of Dunnian (saturation excess) runoff (GW feedback)

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GSFLOW Hydraulics:

Stream Routing

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GSFLOW Hydraulics

► Streams can pick up precipitation, runoff, interflow, groundwater and pipe discharges

► Stream losses to GW, ET, channel diversions and pipelines

► GW Leakage/discharge is based on head difference between aquifer and river stage elevation An extra stream bed conductance layer

exists under each river reach

Similar to MODFLOW rivers, but the head difference is based on total flow river level

River Loss

River Pickup

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(Markstrom et.al., 2008)

GSFLOW: Stream Channel Geometry

► The Stream Flow Routing package (SFR2) represents stream channels using an 8-point cross-section in order to accommodate overbank flow conditions

► Streamflow depths are solved using Manning’s equation

► Different roughness can be applied to in-channel and overbank regions

► SFR2 incorporates sub-daily 1D kinematic wave approximation if analysis of longitudinal flood routing is required

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GSFLOW Application: Water Budget

► Water budgeting, permit allocation and cumulative impact assessment

Sample question: What is the contribution of stream leakage to the aquifer system during the summer?

► GSFLOW Simulation:

Detailed analysis of various components of the stream/aquifer interaction

Sample animations showing summer stream flows and leakage

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Total Streamflow and Hortonian Runoff

► Gradational Stream Color: Total stream flow accumulation

► Background Blue Pulses: Runoff from rainfall events

► Animation shows headwater tributaries flowing after a storm and then drying up during the summer months

► Animation Link

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GW Leakage to Streams

► Blue stream reaches: Streams that pick up water from the GW system

► Red stream reaches: Streams that loose water to the GW system

► Red Pulses: Runoff from storm events raise water levels in the stream and drive water into the aquifer system

► Note reversals in GW/SW gradient

► Animation Link

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Baseflow Discharge

► Gradational Stream Color: Total baseflow discharge to the streams

► Note: During storm events the stream levels rise and reverse the GW/SW gradient (baseflow discharge stops when the stream levels rise)

► Animation Link

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GSFLOW Stream Routing Conclusions

► GSFLOW features:

Streams can be incised in the GW system layers

Interaction is conceptually similar to MODFLOW Rivers, but with total flow routing

Streams can dry up and later rewet

Every component of the stream flow can be identified and visualized

► Limitations: Stream routing simplified when compared to storm water models

Timing and channel flow representation not ideal for peak flow or flood modelling

(However, GW interaction is likely not significant during peak flow analysis)

► Overall benefits for water budgeting and cumulative impact:

Full accounting of gains and losses to the stream network

Ideal for simulation of impact during low flow conditions

Allows calibration to total measured streamflow at the gauge

► Much more direct than trying to calibrate to a baseflow estimate

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GSFLOW Eco-Hydrology Application:

Wetlands, Lakes and Reservoirs

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GSFLOW Application: Eco-Hydrology

► Eco-hydrology broadly includes the assessment of wetlands, streams and fisheries issues

Existing catchment and hydraulic models cannot represent the GW discharge dominated low flow conditions that are essential to understanding the hydroperiod of a wetland

Existing GW models can simulate discharge to wetlands, but without simulating total flow and stage (GW and SW) they may over-estimate

► Issues:

Spring storage and leakage to GW (fill, spill and leak)

Hydroperiod assessment: preservation of temporal water level patterns

GW connection: many lakes and wetlands are both gaining and loosing

Reservoir control structures and water management

Baseflow discharge

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GSFLOW Lakes and Wetlands

► Separate water balance done for each lake to determine y:

► QIN + P – E – QLEAK(y) = QOUT(y)

► Wetlands and lakes can penetrate multiple aquifer layers

► SFR2 handles lake inflows and outflows.

► Outflow can be a fixed rate or determined by stage-discharge

► Multiple inlets and outlets are allowed

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GSFLOW Application: Eco-Hydrology

► Example Application: Evaluate the role of a network of vernal pools, wetlands, quarries and reservoirs in maintaining stream flow across a wellfield

Vernal pools (sloughs): fill in the spring, gradually dry up through the summer

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Example: Surface Water Features

► 475 km of mapped streams

Many reaches are actually riparian wetland complexes

► 338 Wetlands

► 12 Lakes and ponds

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Surface Water Features

► 2 Reservoirs with multiple structures

Gates, stop logs, intakes, and spillways

► 1 Diversion

► 1 Quarry Discharge Point

► Surface Water Takings from permit and water use databases

Quarry

Diversion

Reservoirs

Wellfield

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Simulated Stage in Lakes and

Wetlands

Some Long Riparian wetlands broken into linked

chain

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Simulated GW Seepage

from Lakes and Wetlands

Seepage In (red)

Seepage Out (blue)

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Simulated Seepage from Lakes and

Wetlands

Seepage In (red) Seepage Out (blue)

Most wetlands

show upgradient GW inflows and

downgradient GW outflows

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Seepage In (red) Seepage Out (blue)

Wellfield pumping enhances leakage

from reservoir

Cross section through reservoir/wellfield

Wellfield

Quarry

Reservoirs

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Simulated Stage in Reservoir (as per Operation Rules) Shows Release from Outlets for Flow Augmentation

Actual Operations differ from “Operating Rules”

Constant Head

No-Flow

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GSFLOW Application: Eco-Hydrology

► Conclusions:

GSFLOW can simulated wetlands, lakes and reservoirs that cross-connect multiple aquifer layers

► New MODFLOW-NWT solver can simulate the complex variably saturated wet/dry cells in and around the lakes

Seasonal storage in the wetlands is significant: fill in the spring and drain through the summer

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GSFLOW Hydrology Application:

Soil Zone Processes and Recharge

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GSFLOW Cell-based Hydrology Model

► Fully distributed cell-based model – each cell has unique parameters

Land use, surficial geology, slope, aspect, elevation, etc.

► Interception storage, depression storage and percent imperviousness are all distributed according to the land use mapping

► Snowmelt is handled using a 2-layer energy balance approach

Treats snow pack as a porous medium allowing mass redistribution and refreezing.

Spatial distribution of the snow pack is handled by a locally-derived snow curve.

Frozen soils are modelled using an infiltration limiting rate

► Two forms of runoff generation are modelled:

Infiltration rate capacity (Hortonian flow)

Saturation excess (Dunnian flow)

Soil water

Evapotranspiration

StreamStream

Surface runoff

Precipitation

Infiltration

Surfacerunoff

Interflow

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GSFLOW Hydrology

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GSFLOW: Sub-Cell Processes

Rooftop

Impervious areas & Depression storage

Pervious area

Tree canopy interception

Micro-topographic depressions

• Sub-cell components • Impervious area

• Impervious depression storage • Direct runoff • Option to route water from impervious to pervious areas

• Pervious area • Pervious area depression storage • Canopy interception

Parking

Grass

(1 model cell)

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GSFLOW: Soil Zone

• Soil zone is essentially three integrated reservoirs that fill, drain and spill

• Multiple algorithms available for runoff partitioning

•Linear and non-linear contributing area infiltration routines •SCS) Curve Number (CN) •Green and Ampt (new – hourly option)

Fast & slow interflow

(Tension storage)

Groundwater recharge

(Markstrom et.al., 2008)

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…

Overland runoff

Interflow

To stream channel

GSFLOW: Overland Runoff

► Runoff pathways are defined by digital terrain model

► Both runoff and subsurface/interflow are routed

Pathways represented by a distributed cascade of linear and/or non-linear reservoirs, every cell having their own independent reservoir.

The cascade is continued until a stream or swale (e.g., surficial depressions, hummocky topography) is reached

► Runoff from one cell can infiltrate in an adjacent cell

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GSFLOW Application: Urban Development and LIDS

► Land use change and urbanization considerations:

Need to understand and mitigate increases in runoff

► Aging infrastructure – old sewers cannot handle flows

► Urbanization in upstream portions of a catchment

► Climate change and storm intensity

► Preservation and restoration of urban rivers and wetlands

► Solution: Low Impact Development (LID)

LIDs are used to reduce runoff through enhanced GW infiltration

LID design options include:

► Bioswales, infiltration galleries, permeable pavers, green roofs, etc.

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Sample LIDs Assessment with GSFLOW

► Proposed new development for 70,000 residents

Proposed commercial area

Proposed Low Density Residential

Existing wetlands

GW fed streams and wetlands

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Runoff: Pre-development

► GSFLOW overland run-off and interflow simulated with cascading inter-cell flow network

Till uplands

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Runoff and Interflow Animation

► Soil zone moisture and runoff patterns Animation Link

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Recharge: Pre-development

► GW Recharge is not one-dimensional but includes both re-directed runoff and vertical infiltration

Higher recharge at the geologic contact due to re-infiltration of runoff

Till uplands

Coarser grained beach deposits

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Recharge: Post-development (no LIDS)

► Simulations indicate local wetland and stream features affected by both changes in runoff and recharge

Lost recharge due to land use change

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Recharge: Post-development (no LIDS)

► Lower recharge and runoff from the residential lots

Lost recharge and wetland discharge to due to both development and runoff

changes

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Recharge: Post-development (with LIDS)

► Simulations of residential LIDs (roof leaders to yards) and larger scale LID features (3rd pipe infiltration galleries and ponds)

Unlined ponds added to enhance infiltration in

vicinity of wetlands Infiltration gallery under commercial

developments

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Regional Level LIDS Assessment

► Simulation of catchment scale GW discharge patterns

High baseflow discharge

GW discharge to stream and wetlands

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Conclusions: Integrated Modelling

► When is integrated GW/SW modelling really necessary?

Whenever there is significant stress that might cause water movement between zones (soil/channel/aquifer)

► Integrated model calibration: both flows and levels

From a GW perspective, integrated modelling actually simplifies the calibration because it allows direct calibration to observed precipitation and measured stream flow

► Choosing an integrated model:

Is the simulation process scale and resolution (spatial and temporal) consistent and balanced?

► Why choose a peak flow channel model coupled to a GW model?

Need to think about the coupling zones:

► Shallow layer geometry and wet/dry layers

► Refinements in the areas of interest

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Conclusions: GSFLOW

► GSFLOW: An integrated model designed by hydrogeologists

A groundwater model with surface water processes

MODFLOW, but significantly adapted to handle shallow wet/dry problems

► Ideal for:

Analysis of cumulative impact of GW takings on SW features

Eco-hydrology, fisheries, drought and low-flow condition analysis

Problems involving pits, lakes and wetlands that incise one or more subsurface layers

► Not for:

Surface water storm flows, peak flows, flood waves

Detailed in-channel flow and level simulation

“Flashy” catchments

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Integrated Modelling: Insights

► Infiltration and recharge are 3D processes

► Recharge is much more variable than you think

► Hydrologists now think that subsurface layer geometry drives runoff

Google “old water paradox” and the 2011 Birdsall-Dreiss Lecture

You will need to rethink your shallow layer conceptual model

► You cannot independently calibrate the SW and GW components and then “slap” them together

If you could, you probably don’t need an integrated model