Annual Groundwater Discharge Research Articles

Effects of climate change on the groundwater system in the Grote-Nete catchment, Belgium

The effects of climate change on the ground- water systems in the Grote-Nete catchment, Belgium, covering an area of 525 km 2 , is modeled using wet (greenhouse), cold or NATCC (North Atlantic Thermoha- line Circulation Change) and dry climate scenarios. Low, central and high estimates of temperature changes are adopted for wet scenarios. Seasonal and annual water balance components including groundwater recharge are simulated using the WetSpass model, while mean annual groundwater elevations and discharge are simulated with a steady-state MODFLOW groundwater model. WetSpass results for the wet scenarios show that wet winters and drier summers are expected relative to the present situation. MODFLOW results for wet high scenario show groundwater levels increase by as much as 79 cm, which could affect the distribution and species richness of meadows. Results obtained for cold scenarios depict drier winters and wetter summers relative to the present. The dry scenarios predict dry conditions for the whole year. There is no recharge during the summer, which is mainly attributed to high evapotranspiration rates by forests and low precipitation. Average annual groundwater levels drop by 0.5 m, with maximum of 3.1 m on the eastern part of the Campine Plateau. This could endanger aquatic ecosystem, shrubs, and crop production.

EVALUATION OF THE ASSUMPTION OF WATERTIGHT BEDROCK UNDERLYING AN EXPERIMENTAL WATERSHED

The long-term studies of water and chemical budgets in the Hubbard Brook watershed, White Mountains, New Hampshire, have assumed that the underlying bedrock is watertight and that all of the liquid water discharged from the experimental subcatchment areas was measured using stream gauging instrumentation. This paper reviews the evidence used by past workers to support this assumption. In a reanalysis of the reported relationship between precipitation inputs and stream outputs of chloride, the mean annual groundwater discharge beneath the stream gauging stations was computed to be at least 5–10% of the mean annual precipitation. Groundwater discharge of this quantity would change both the evapotranspiration and the rock-weathering rates reported for the Hubbard Brook watershed. On-site hydrogeological field tests are recommended in all watersheds that are assumed to be underlain by watertight bedrock. [Key words: forested ecosystems, groundwater hydrology, bedrock fractures, water budgets, evapotranspirati...

Groundwater recharge and discharge response to rainfall on a hillslope

Groundwater recharge was investigated within a representative hillslope segment of a small forested catchment, where the depth to the water table increased when progressing upslope from a free water outlet. Catchment soils varied with progression upslope from grey through yellow to red earths, which were underlain by low hydraulic conductivity B horizons and permeable substrata. The catchment was equipped for measuring stream discharge, rainfall characteristics, water table position, soil water content and soil hydraulic properties. Measurements commenced when soil water was severely depleted by drought, and were continued to monitor infiltration and redistribution with depth after more than 1000 mm of rainfall. Water movement occurred under approximately unit hydraulic gradients to the layer of restricted hydraulic conductivity; with movement through this layer proceeding under gradients considerably in excess of unity. Between rainfall events water movement in the soil profiles with deep water tables occurred by redistribution, with the capillary flux exceeding the gravitational flux. Where water tables were shallow (<m), profile recharge occurred within 7 weeks, after which sustained recharge to the groundwater body occurred at rates of the order of 3 mm day-1. Where water tables were deep (>7 m) it took many months for the soil water deficit to be replenished by rainfall. Recharge to groundwater in this case commenced with a flux of about 0.5 mm day-1 and decreased to an estimated value of 0.3 mm day-1 some 5 months later. Following winter rain more than 30% of the annual groundwater discharge from the catchment originated from a relatively small but expanding area near the free water outlet.