Hydrology of Alpine Lake Waiau, Mauna Kea, Hawaii
Abstract
Alpine Lake Waiau, located at 3965 m above sea level on the summit of Mauna Kea, Hawaii, is part of a unique glacial-volcanic landscape that has deep historical and cultural significance for Native Hawaiians. Using topographic information, daily meteorological data from August 1999 to February 2002, and calibration with lake level and isotope measurements taken in August 1999 - 2001 and February 2002, a one dimensional hydrologic model of the lake was constructed that provides daily estimates of lake depth and oxygen and hydrogen isotope ratios. The model incorporates evaporation as modeled by the Penman equations, a weir equation governing spillover from the basin into Pohakuloa gulch, and a linear reservoir model that introduces a lag time for input to the lake from waters falling into the basin from precipitation events. Further, meteoric precipitation was characterized by isotopic analysis of samples collected at different altitudes. The model also predicts the isotopic composition of lake water based on the mixing of existing lake water and precipitation, spillover, and evaporation. A non-linear multidimensional minimization method was used to optimize values for five constrained but unknown parameters: two linear reservoir parameters, mean time for runoff to enter the lake and the percent of water falling into the basin that actually enters the lake, evaporation fractionation factors for hydrogen and oxygen isotopes, and rate of water loss through the permeable basalt layer encircling the upper lip of the lake basin. Modeling results demonstrate that the source of water is surface runoff from precipitation that falls within a restricted drainage basin; isotopic compositions permit no other groundwater inputs. Outflow occurs by spillover during high stands and by extensive evaporation; the lake bed is essentially impermeable and prevents loss to seepage. Most inflow is from a few large winter precipitation events that cause the lake to spillover and the lake waters to become isotopically light. For the rest of the year, evaporation dominates, lake level drops, and the lake becomes isotopically heavy. Because it has a drainage basin limited to the Pu'u Waiau cinder cone, Lake Waiau is not threatened by septic waters that drain from the mountain's telescope observatories; but it may be in danger of drying out during droughts associated with enhanced El Niño events linked to greenhouse warming.
- Publication:
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AGU Spring Meeting Abstracts
- Pub Date:
- May 2002
- Bibcode:
- 2002AGUSM.H51E..06E
- Keywords:
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- 1803 Anthropogenic effects;
- 1833 Hydroclimatology;
- 1857 Reservoirs (surface);
- 1899 General or miscellaneous