Geology Reports⌕ Search

Geology topics

G. C. Lines

Publications and source records attributed to G. C. Lines.

6 recordsLinked to original sources
USGS2000

Channel incision and patterns of cottonwood stress and mortality along the Mojave River, California

In 1995, mapping and classification of riparian vegetation along the Mojave River in southern California revealed an 8-km reach in which riparian cottonwoods ( Populus fremontii Wats.) were stressed or dying. We tested a set of predictions based on the inference that cottonwood decline was an indirect result of lowered water-table levels following flood-related channel incision. Comparisons of topographic cross-sections from 1963 and 1997, indicated a net change in channel elevation between −0·71 and −3·6 m within zones of cottonwood stress and mortality. Ages of young cottonwood and willow stems adjacent to the present channel and radial stem growth of surviving cottonwoods were consistent with the inference that channel incision, associated with sustained flooding in January and February of 1993, lowered channel elevations throughout the affected reach. Well records and soil redoximorphic features indicate that channel incision caused net water-table declines ⩾1·5 m on portions of the adjacent flood plain where cottonwood stand mortality ranged between 58 and 93%. In areas where water-table declines were estimated to be <1·0 m, stand mortality was 7–13%.

Journal of Arid Environments↗
USGS1988

Water resources of Borrego Valley and vicinity, San Diego County, California: Phase 2 - Development of a ground-water flow model

Because of the imbalance between recharge and pumpage, groundwater levels declined as much as 100 ft in some areas of Borrego Valley, California during drinking 1945-80. As an aid to analyzing the effects of pumping on the groundwater system, a three-dimensional finite-element groundwater flow model was developed. The model was calibrated for both steady-state (1945) and transient-state (1946-79) conditions. For the steady-state calibration, hydraulic conductivities of the three aquifers were varied within reasonable limits to obtain an acceptable match between measured and computed hydraulic heads. Recharge from streamflow infiltration (4,800 acre-ft/yr) was balanced by computed evapotranspiration (3,900 acre-ft/yr) and computed subsurface outflow from the model area (930 acre-ft/yr). For the transient state calibration, the volumes and distribution of net groundwater pumpage were estimated from land-use data and estimates of consumptive use for irrigated crops. The pumpage was assigned to the appropriate nodes in the model for each of seventeen 2-year time steps representing the period 1946-79. The specific yields of the three aquifers were varied within reasonable limits to obtain an acceptable match between measured and computed hydraulic heads. Groundwater pumpage input to the model was compensated by declines in both the computed evapotranspiration and the amount of groundwater in storage. (USGS)

California↗