USING GROUND-WATER FLOW SIMULATIONS FOR PRELIMINARY CHARACTERIZATION OF PEATLAND HYDROLOGY IN THE KENAI PENINSULA LOWLANDS, ALASKA

Mapping identified 41% of the land outside of the Kenai National Forest within the Alaskan Kenai Peninsula Lowlands as wetland. About half (54%) of these wetlands are peatlands. While the hydrologic assessment of peatlands within the Kenai Peninsula Lowlands has been identified by local environmental groups as an important step in evaluating these systems, little hydrologic information is readily available to characterize these wetland systems. To better understand the broad hydrologic and geologic factors influencing the wetlands of the Kenai Lowland, cross-sectional ground-water flow models, based on the geologic profiles, were constructed to evaluate the relationship between ground-water hydrology and wetland function for use by pubic stakeholders.

Ground-water simulations were constructed using MODFLOW-96 in areas that contained wetlands of interest and focusing on larger peatland systems. Broad ground-water flow models extending beyond areas of interest were constructed so robust hydrogeologic boundaries could be assigned at the edge of each model. Flow lines on these profiles were created with Modpath by tracking water particle through the ground-water flow simulations. Cross sections illustrating ground-water flow patterns across four profiles were generated with expanded views produced in areas with significant peatland systems. Sensitivity analysis was performed on recharge and the hydraulic conductivity of different geologic units to identify the parameters that exert the greatest control on peatland hydrology.

Simulations suggest that ground water discharges to most peatland systems; however, regional ground-water moves slowly and only supplies small amounts of minerotrophic water to peatlands. Flowlines indicate that regional ground-water flow that discharges to peat deposits moves laterally primarily within the lower portion of the peat deposit and are isolated from the peat surface. Ground-water simulations were relatively insensitive to changes in recharge, and only changed significantly when recharge was lowered to 10% of the baseline recharge rates. Simulations were very sensitive to changes in bedrock hydraulic conductivity, with peatlands shifting to recharge systems when bedrock hydraulic conductivity was high and discharge systems when the bedrock hydraulic conductivity was low.