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Simulating hydrologic response to climate change and drought with an

integrated surface water/groundwater model

Lake Simcoe watershed

CWRA 2014 E.J. Wexler1, P.J. Thompson1, S.E. Cuddy2, K.N. Howson2,

M.G.S. Takeda1, Dirk Kassenaar1

¹Earthfx Incorporated, Toronto, Ontario ²Lake Simcoe Conservation Authority, Newmarket, Ontario

Presented by Dirk Kassenaar, Earthfx Inc.

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Drought and Climate Change Analysis with Integrated GW/SW Models

► The Water Budget drought assessment component of the Source Water Protection program has driven the analysis of water supply sustainability in Ontario Some Tier 3 studies have utilized powerful fully integrated SW/GW models to

complete this assessment

► The Lake Simcoe Protection Plan (LSPP) has adopted key elements of the SWP drought assessment approach

► The purpose of this presentation is to show how the insights from an integrated LSPP model, developed for drought analysis, can be extended to provide further insights into the assessment of climate change

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Integrated GW/SW Modelling

► Water simply does not care what we call it (SW or GW) and it moves seamlessly between domains

► Our experience is that integrated modelling provides insights that simply cannot be obtainable from uncoupled models Integrated models are 10x tougher

to build, but 100x more insightful!

► Integrated modelling forces you to look at your “blind spots”

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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 3: Hydraulics (MODFLOW SFR2 and

Lake7)

Zone 3: Groundwater (MODFLOW-NWT)

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► GSFLOW is the USGS’s preferred tool for Climate Change Assessment Hydrology: USGS PRMS (Precipitation-Runoff Modelling System)

GW Flow: MODFLOW-NWT: (A new version of MODFLOW optimized for shallow variably saturated (wet/dry) layers

Hydraulics: Lake and SFR2 River Routing Package

► GSFLOW is free and open source model

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GSFLOW SW/GW/SW Components

► Hydrology (PRMS) GW (MODFLOW-NWT) Hydraulics (SFR2)

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Oro Moraine Study Area

► Under the LSPP, a water-budget model was needed for the Oro North, Oro South, and Hawkestone Creek subwatersheds

► The Oro Moraine is a sand and gravel deposit that feeds the headwaters of these catchments.

► Proposed approach:

Develop a fully-integrated GSFLOW model representing the hydrology, GW flow, stream and wetland hydraulics of the entire moraine

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Oro Moraine Study Area

Oro Moraine

Study watersheds

► Three watersheds contributing to the northwestern shores of Lake Simcoe

Oro North

Hawkestone

Oro South

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Geology

► The Oro Moraine has high groundwater recharge but also high groundwater storage

Oro Moraine

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Hydrogeologic Model Layers

► A complex 3D geologic model was available from the OGS

► Too often, hydrogeologists need to simplify the shallow aquifer systems because of model stability and unsaturated model performance issues

► GSFLOW provides a GW submodel that can simulate seepage faces, springs, and thin surficial sand deposits that can be seasonally important Particularly for important for vernal pools, wetlands and headwater creeks

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Hydraulics and Eco-Feature Representation

► Our approach was to represent all streams in the model, even the intermittent Strahler Class 1 streams

► Over 85 Lakes, Ponds, and Lake/Wetlands

► Wetlands accounted for both hydraulically (LAK) and hydrologically (Soil Moisture Accounting package)

► Continuous fully coupled GW/SW interaction

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Oro Moraine

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Hydrology: Precipitation

► Calibrated hourly NEXRAD radar data was found to provide the best estimate of distributed precipitation

► NEXRAD cells represented as Virtual Climate Stations (VSCs) spaced ~4.5 km apart across the study area

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NEXRAD VCS

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Hydrology: Topography and Runoff

► 50-m DEM used to generate cascade flow paths to route overland runoff to streams

► Slope aspect used for ET and snowmelt modules

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Hydrology: Predicted Average Recharge

► Average recharge from a 32-yr simulation

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Predicted GW Levels: Layer 1 and 7

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► Coldwater River at Coldwater (02ED007)

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Continuous Streamflow Simulation

Observed (blue) Predicted (red)

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Aquifer Head vs. Stream Stage

Groundwater discharging to the

stream, except during large events

Hydrograph at Oro-Hawkstone stream gauge

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Model Development Conclusions

► The integrated GSFLOW model represents the entire SW+GW system, including:

Very detailed geologic layering, including complex partially saturated shallow aquifers

Fully distributed hydrology, overland flow and interflow Hourly NEXRAD precip inputs.

All streams and wetlands, including even the smallest intermittent streams and headwater springs

Full stream routing, with complex GW/SW discharge reversals during storm events.

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DROUGHT ASSESSMENT

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Selected 10-Year Drought Period

► Recent and relatively prolonged drought More climate and streamflow data than the 1930’s

Similar land use

► Hourly climate data from local MNR In-filled Climate Stations (BARRIE WPCC, COLDWATER WARMINSTER, MIDHURST, ORILLIA BRAIN)

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1953-1967

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Predicted monthly flows before and during 10-year drought

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2000

4000

6000

8000

10000

12000

14000

16000Ja

n-5

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Jul-54

Jan-5

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Jul-55

Jan-5

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Jul-56

Jan-5

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Jul-57

Jan-5

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Jul-58

Jan-5

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Jul-59

Jan-6

0

Jul-60

Jan-6

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Jul-61

Jan-6

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Jul-62

Jan-6

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Jul-63

Jan-6

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Jul-64

Jan-6

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Jul-65

Jan-6

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Jul-66

Jan-6

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Mo

nth

ly A

ve

rag

e G

rou

nd

wa

ter

Dis

ch

arg

e

to S

tre

am

s

(m3/d

ay)

Hawkstone Oro South Oro North

Compares typical late summer flows with drought flows

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August 1957 November 1964

Monthly flows before and during 10-year drought

Many of smaller tributaries have dried up. Oro South Creeks affected most because they are not fed directly by Oro Moraine.

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10-Year Drought

► Figure shows decrease in average monthly flow at worst point in drought compared to start of drought

► Decreases occur in all tributaries

► Change in flow or minimum flows can be set as drought triggers

► Flows can be used to estimate effects on fish habitat

Decrease in average monthly streamflow (m3/s)

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10-Year Drought

► Limited drought impact in Oro North

► Moderate change in Hawkstone tribs

► Large, severe change in Oro South tribs and main branch

► Drought sensitivity depends on whether streams are linked to Oro Moraine or recharged locally

Percent change in average monthly streamflow

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GW Discharge to Wetlands

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

Soil-zone base

Surface Discharge

► “Surface Discharge” is the movement of water from the GW system to the soil zone, where it can become interflow or surface runoff

► Saturated soils can reject recharge: groundwater feedback

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Contributing Area/GW Feedback

• Areas of high water table (red) contribute Dunnian runoff to streams.

• Significant seasonal and drought change in contributing area

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Areas of high Water Table and Stream Flow

• Areas of high water table contribute Dunnian runoff to streams.

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Groundwater Seepage to Hawkestone Creek

• GW seepage (green lines) in the reach near the Hawkestone WSC stream gauge.

• Not much change during drought. Other reaches more sensitive

• Daily seepage shows reversal of gradients (seepage losses) during periods of high streamflow (blue line) and stream stage.

• Gradients restored after peak stage passes.

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Hydrograph shows groundwater seepage along Hawkestone Creek. Seepage is controlled by till thickness and aquifer geometry. Seepage decreases during drought.

August 1957 November 1964

GW discharge where aquifer pinches and forces water to surface

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Section line is through the two watersheds. Differences in the till thickness and the aquifer continuity affect the behavior of the streams in Hawkstone and Oro South Hawkstone runs along the base of the moraine cutting off flow to South Oro

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Drought Simulation Conclusions

► Changes in simulated flows at the gauge don’t always tell the whole story

► Change in tributary response can be very different between apparently similar catchments

South Oro – Major change in both tributary and main branch response

Hawkstone – Significant change in tributaries

North Oro – Little change in trib or main branch drought flows

► Understanding the underlying geology is essential

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CLIMATE CHANGE ASSESSMENT

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Building on the Drought Analysis

► Simulation of recent droughts provides an excellent foundation for climate change analysis

► The drought analysis provides:

Insights into the complex behaviour at both the watershed and tributary scale

An excellent “stress test” for the model

► We now have a good understanding of the system, and a framework for climate change assessment

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Climate Change in Ontario ► Average of 30 GCM-scenarios a show 2 to 4C temp. increase by 2050.

About double the global estimate.

► Changes in extreme warm temperatures expected to be greater than changes in annual mean temperature

Number of days above 30°C to double

More heat wave and droughts.

► Annual precip. will increase up to 10% in S. Ontario, but

Summer and fall total rainfall may decrease by up to 10%

Winter precip. may increase up to 10% in south

Less precipitation as snow; more lake effect snow though.

Rainfall intensity and frequency of intense events likely to increase

► How will the Oro watersheds respond?

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GCM models of Climate Change

► Many different climate models.

► Predictions of annual temperature and precipitation increase cover a wide range

► GW/SW models can be run with a range of CM predictions to bracket range of likely outcomes

Selected by Percentile

Modelled for this Study

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Downscaling GCM Models ► Climate predictions are done with Global Circulation Models (GCM).

Grid scale is large (250 - 400 km cells).

Results are in terms of annual, seasonal, monthly change.

Each model has different predictions based on different greenhouse gas (GHG) emissions scenarios

► Different methods are available for downscaling GCM outputs for use in local-scale models

Change Field method was selected for this analysis

► Shift mean of local observed data (e.g. Temp)

► Multiply values by scale factor (e.g. Precip)

Shift can be on a monthly, seasonal, or annual basis.

► Selected approach does not change frequency or intensity of storms

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Temperature - Baseline versus CGCM3T63

Daily and Monthly Baseline Temperature versus CGCM3T63 Values shifted by 1.4 to 4.6 C

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Precipitation - Baseline versus CGCM3T63

Daily and Monthly Baseline Precipitation versus CGCM3T63 Values scaled by -15 to 46%

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Change in Total Streamflow – Bluffs Creek (North Oro)

• More flow in winter months.

• Spring freshet is earlier

• Very little change in summer flows

• Strongly GW dominated.

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Change in Total Streamflow - Hawkestone Creek

• More flow in winter months.

• Spring freshet is earlier

• Not much change in summer flows – volumes are similar

• Main branch has a significant GW component

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Change in Total Flow – Shellswell Creek (South Oro)

• Similar results.

– More flow in winter months.

– Spring freshet is earlier

• However - Smaller change in summer flows

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Change in Total Streamflow – Oro South

• Log Scale: Shows significant reduction in summer flows

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Simulated Change in Total Streamflow - Coldwater River

Again, reduction in summer flows, but not as severe given contact with the GW system

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Comparison of Low Flow Change – Bluffs vs Shellswell Creek

• Similar change in winter patterns, change in South Oro Creeks is more pronounced in summer

Shellswell Creek (South Oro)

Bluffs Creek (North Oro)

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Comparison of Flow Change – Bluffs vs Shellswell Creek

Shellswell Creek (South Oro) Bluffs Creek (North Oro)

• Little change in runoff events, change in low flow conditions more pronounced in Oro South

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Change in Baseflow (Hyporheic Exchange) - Hawkestone Creek

• GSFLOW simulates the true baseflow component of total streamflow

• Baseflow analysis provides insight into GW storage and release.

• Much more baseflow in winter months.

• Some decrease in summer baseflow, but well connected to the Moraine

• Very significant change in the timing and quantity of groundwater inflows during the spring months (no freshet to recharge the GW system in the mid to late spring)

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Contributing Area: High Water Table GW Feedback

• Areas of high water table (red) contribute Dunnian runoff to streams.

• Significant seasonal and drought change in contributing area

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Areas of high Water Table and Stream Flow

• Areas of high water table contribute Dunnian runoff to streams.

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Climate Change: Conclusions

► As with the drought analysis, changes in simulated flows at the gauge don’t always tell the whole story

More recharge and baseflow discharge in the winter

Drought sensitive reaches will be further stressed in the summer

Marginal reaches will become even more marginal

► Understanding the underlying geology is essential

Interconnection to aquifer storage is key

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Integrated Modelling: Conclusions

► Integrated modelling can provide locally detailed insights into the behaviour of specific creeks and tributaries

This example shows how three apparently similar creeks can exhibit significantly different drought and climate change response.

► Integrated models built for drought or low flow analysis are well suited for climate change assessment

Logical extension of the SWP program work

► Other issues, such as eco-hydrology, ESGRA analysis, LIDS, urbanization, recharge protection and even flow regime assessment can be studied

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Baseline Click for Animation CGCM3T63

Thank you! Questions or Comments?