The Caveat: Hydrology

• Complex

• Site specific

• Difficult to accurately quantify

• More questions than answers

Wetland Hydrology

• Wetland Hydrologic Function– Flow control– Water quality

Current projects to assess function

• Landscape scale diagrams (RSE)

• Wells (Gracz and Coble)

• Conceptual, regional model (Andy Reeve)

A few terms

• Recharge, discharge– Recharge = input; discharge = output

• Water Budget+ Precipitation– ET– Storage– Average Streamflow– Storm and spring melt Streamflow– Groundwater flow

• Confined/unconfined aquifers

Landscape Diagrams (RSE)

• Geology

• Nature of confined and unconfined aquifers

• Basic water budget

Complex, thick glacial sediments, some produce artesian flows

Thick, complex glacial sediments. Note two till units N of Kenai River.

Abandoned, connected channel deposits- withdrawal from these may induce recharge from streams.

Mostly thin glacial sediments.Groundwater discharge to peatlands from surrounding highlands

Very thin glacial sediments, most (shallow unconfined) groundwater movement occurrs in a near-surface zone

Wells (Gracz and Coble)

• Document Wetland Hydrology over the growing season

• Describe nature of precipitation storage

• Begin to understand ET where possible

Growing Season and Wetland Hydrology

• Homer Airport Growing Season: May 8- Oct 2

• In Wellheads:

• Begin 2006• 17 April (Homer Bench)• 6 June (Skyline)• 4 June (Blackwater Bend)

• End 2005• 24 October (Homer Bench)• 2 September (Skyline)• 11 October (Blackwater Bend)

Wynn Nature Center Bog

H234 Water level and Precipitation

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Date

Wat

er L

evel

, Fee

t

0.00

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1.00

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Prec

ip, I

nche

s

Water level Precip

Summer: Water table drops, less in 2006Fall: rapidly rises with onset of rainy period,Winter: remains steady, then slowly lowers during late winterSpring: rapidly rises during snowmelt period

Homer Bench near Beluga Lake

Calvin and Coyle Bluejoint- Willow Discharge Slope (SCS) Precip and Water Level, Well #2

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1.00

1.20

Aug-0

5

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Oct-05

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5

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5

Jan-

06

Feb-0

6

Mar

-06

Apr-0

6

May

-06

Jun-

06

21-J

un1-

Jul

5-Ju

l

10-J

ul

11-J

ul

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ul

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ul

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ul

25 Ju

l

1 Aug

5 Aug

10 A

ug

Sep-0

6

Inch

es P

reci

p

-4

-3

-2

-1

0

1

40" deep, fully screened

Wat

er L

evel

, Fee

t

Precip Water Level

Summer: Drops to confining layerFall: rapidly rises with onset of rainy periodWinter: varies, probably responding to freeze/thaw cyclesSpring: rises with snowmelt period

Homer Bench below Paul Banks Elem.

Calvin and Coyle Spruce / Alder Discharge Slope (SLA) Precip and Water Level, Well #2

0.00

0.20

0.40

0.60

0.80

1.00

1.20

Aug-0

5

Sep-0

5

Oct-05

Nov-0

5

Dec-0

5

Jan-

06

Feb-0

6

Mar

-06

Apr-0

6

May

-06

Jun-

06

21-J

un1-

Jul

5-Ju

l

10-J

ul

11-J

ul

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ul

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ul

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ul

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ul

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ul

25 Ju

l

1 Aug

5 Aug

10 A

ug

Sep-0

6

Inch

es P

reci

p

-4

-3

-2

-1

0

1

38" deep, fully screened

Wa

ter

Lev

el,

Fee

t

Precip Water Level

Summer: dropped to confining layer in 2005, but not 2006Fall: rises rapidly with onset of rainy periodWinter: small drops and rises probably corresponding to thaw cyclesSpring: rises a little, but little storage is available for spring melt

Blackwater Bend

Peatland:Summer: lots of variation, but general dropFall: rapid rise with onset of rainy periodWinter: remains steady, but varies late winter; -discharge to stream during January?Spring: rapid rise during melt

Discharge Slope: remains close to surface year aroundSummer: lots of sharp variationFall: general rise, then remains relatively steady near surfaceWinter: remains steady, but varies late winter is recharged by peatland above?Spring: drop after melt period.

Where does the discharge go?

• Atmosphere (ET)

• Adjacent wetlands and streams

• Deeper groundwater

ET- Evapotranspiration

• Thornthwaite Equation using temperature– Found to underpredict actual ET

• Daily water table variations– Need specific conditions

Daily Water Table Variations

SLA Water Table, 9 - 16 July 2006

-1.2

-1.1

-1.0

-0.9

-0.8

-0.7

-0.6

-0.5

10-J

ul

11-J

ul

12-J

ul

13-J

ul

14-J

ul

15-J

ulDe

pth

Be

low

Su

rfa

ce,

Fe

et

Plants use water during the day

Recharge occurs at night

ET Varies

• Equation generally agrees with water table variations

• Predictions more or less verified by actual stream flow values

• Could be as high as 85% of annual precipitation- in forest behind Paul Banks

• Probably low at peatlands

So far we can GUESS:

• If annual precipitation equals 24”:

• 14” leaves as ET• 3” remains in storage- cycling over the year• ¾” goes to deeper groundwater• 2¾” leaves as storm and spring melt run-off• 3½” Flows in streams during “normal” periods

Conceptual, Regional Model (Andy Reeve, Univ. Maine)

• Generally: How does water move throughout the regions shown in the Landscape diagrams

• MODFLOW hydrologic computer model• Precipitation• Elevation/slope• Guesses at hydraulic conductivity

Abandoned channel deposits: more or less continuous.

Most discharge (of moisture surplus) is to streams, -between 0 and 16% of the moisture surplus is discharged to peat from local uplands. -peat remains saturated during dry periods; streamflow suffers

Pumping from shallow wells may induce recharge from streams.

Springs indicate groundwater discharge from highlands to peatland.

Most flow is from shallow unconfined aquifer to confined, but some into river.

Between about 3 and 17% of moisture surplus leaves to deeper aquifers.

Overall Conclusions

• Diagrams: – Thin unconfined aquifer near Homer

• Wells: – Storage is significant and can be replenished during

winter. – ET can be large in forested wetlands

• Model: – Wetlands remain saturated during dry years;

streamflow suffers.