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The Caveat: Hydrology

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)

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The Caveat: Hydrology

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  1. The Caveat: Hydrology • Complex • Site specific • Difficult to accurately quantify • More questions than answers

  2. Wetland Hydrology • Wetland Hydrologic Function • Flow control • Water quality

  3. Current projects to assess function • Landscape scale diagrams (RSE) • Wells (Gracz and Coble) • Conceptual, regional model (Andy Reeve)

  4. 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

  5. Landscape Diagrams (RSE) • Geology • Nature of confined and unconfined aquifers • Basic water budget

  6. Complex,thick glacial sediments, some produce artesian flows

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

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

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

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

  11. Wells (Gracz and Coble) • Document Wetland Hydrology over the growing season • Describe nature of precipitation storage • Begin to understand ET where possible

  12. 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)

  13. 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

  14. 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

  15. 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

  16. 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.

  17. Where does the discharge go? • Atmosphere (ET) • Adjacent wetlands and streams • Deeper groundwater

  18. ET- Evapotranspiration • Thornthwaite Equation using temperature • Found to underpredict actual ET • Daily water table variations • Need specific conditions

  19. Daily Water Table Variations Plants use water during the day Recharge occurs at night

  20. 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

  21. 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

  22. 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

  23. 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.

  24. 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.

  25. 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.

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