the caveat: hydrology complex site specific difficult to accurately quantify more questions than...
TRANSCRIPT
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The Caveat: Hydrology
• Complex
• Site specific
• Difficult to accurately quantify
• More questions than answers
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Wetland Hydrology
• Wetland Hydrologic Function– Flow control– Water quality
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Current projects to assess function
• Landscape scale diagrams (RSE)
• Wells (Gracz and Coble)
• Conceptual, regional model (Andy Reeve)
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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
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Landscape Diagrams (RSE)
• Geology
• Nature of confined and unconfined aquifers
• Basic water budget
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Complex, thick glacial sediments, some produce artesian flows
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Thick, complex glacial sediments. Note two till units N of Kenai River.
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Abandoned, connected channel deposits- withdrawal from these may induce recharge from streams.
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Mostly thin glacial sediments.Groundwater discharge to peatlands from surrounding highlands
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Very thin glacial sediments, most (shallow unconfined) groundwater movement occurrs in a near-surface zone
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Wells (Gracz and Coble)
• Document Wetland Hydrology over the growing season
• Describe nature of precipitation storage
• Begin to understand ET where possible
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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)
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Wynn Nature Center Bog
H234 Water level and Precipitation
-9.0
-8.0
-7.0
-6.0
-5.0
-4.0
-3.0
-2.0
-1.0
Date
Wat
er L
evel
, Fee
t
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
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
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Homer Bench near Beluga Lake
Calvin and Coyle Bluejoint- Willow Discharge Slope (SCS) 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
12-J
ul
13-J
ul
14-J
ul
15-J
ul
20-J
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
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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
12-J
ul
13-J
ul
14-J
ul
15-J
ul
20-J
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
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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.
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Where does the discharge go?
• Atmosphere (ET)
• Adjacent wetlands and streams
• Deeper groundwater
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ET- Evapotranspiration
• Thornthwaite Equation using temperature– Found to underpredict actual ET
• Daily water table variations– Need specific conditions
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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
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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
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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
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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
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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.
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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.
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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.