New Mexico Geological Society Annual Spring Meeting — Abstracts

Discharge per unit area difiers in both magnitude and timing during spring snowmelt in six adjacent northern New Mexico watersheds. Gneiss and granite underlie two basins, which have high unit discharges (0.010-0.014 m³/s /km²) and high median basin elevations (3300-3420 m). Sandstone and shale underlie the remaining four basins, which have low unit discharges (0.001-0.005 m³/s /km²) and low median basin elevations (2860-3000 m).

Lithology and topographic relief within a watershed appear to control the magnitude of unit discharge in the two terranes. Snowmelt during April and May at lower elevations produces steep hydrographs in both terranes, with discharge per unit area in crystalline terrane being higher presumably due to lower permeabilities. Late-spring runoff is higher in crystalline terranes due to deeper average snowpack in these basins, which have more area at higher elevations. Broad spring hydrographs are characteristic of crystalline terrane, but in sedimentary terrane streamflow recedes quickly after mid-May peaks. This suggests that meltwater storage and return flow are substantial in the crystalline terrane but not in the sedimentary terrane. Glacial deposits underlie approximately 30% of the basins in crystalline terraner these appear to act as storage reservoirs, delaying discharge recessions until mid-June. Steeper hydrograph recessional limbs for streams in the sedimentary terrane, of which less than 10% contains glacial deposits, are apparently due to relatively low amounts of meltwater storage. Thus, three factors control hydrologic conditions in the study area: areaI elevation distributions, which control the timing and amounts of water input; lithology, which controls runoff amounts in areas having minor storagee and glacial deposits, which control discharge duration and timing via storage and return flow releases.