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 Summer: Water table drops, less in 2006 Fall: rapidly rises with onset of rainy period, Winter: remains steady, then slowly lowers during late winter Spring: rapidly rises during snowmelt period
Homer Bench near Beluga Lake Summer: Drops to confining layer Fall: rapidly rises with onset of rainy period Winter: varies, probably responding to freeze/thaw cycles Spring: rises with snowmelt period
Homer Bench below Paul Banks Elem. Summer: dropped to confining layer in 2005, but not 2006 Fall: rises rapidly with onset of rainy period Winter: small drops and rises probably corresponding to thaw cycles Spring: rises a little, but little storage is available for spring melt
Blackwater Bend Peatland: Summer: lots of variation, but general drop Fall: rapid rise with onset of rainy period Winter: remains steady, but varies late winter; -discharge to stream during January? Spring: rapid rise during melt Discharge Slope: remains close to surface year around Summer: lots of sharp variation Fall: general rise, then remains relatively steady near surface Winter: 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 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.