Estimation of shallow ground-water recharge in the Great Lakes basin

Abstract

iv "Water Budget Myth" (Bredehoeft, 1997). Even further misinterpretations sometimes are made that if groundwater withdrawals are less than the recharge rate, then water levels and groundwater storage will not decline. To understand the fallacy of the misperception described above, one needs to consider how groundwater systems respond to withdrawals. Under natural (non-pumping) conditions, a groundwater system is in long-term equilibrium. That is, averaged over some period (and without considering possible long-term climate change), the amount of water recharging the system is approximately equal to the amount of water leaving or discharging from the system. Groundwater withdrawals by pumping change the flow system. The water that is withdrawn must be supplied by some combination of (1) increased recharge, (2) decreased discharge, and (3) removal of water that was stored in the system. Regardless of the amount of water withdrawn, the groundwater system will undergo some drawdown in water levels in pumping wells to induce the flow of water to these wells. Thus, some water is removed from storage. For most groundwater systems, the change in storage in response to pumping is a transient phenomenon that occurs as the system adjusts to the withdrawals. The relative contributions of changes in storage, changes in recharge, and changes in discharge evolve with time. If the system can come to a new equilibrium, the changes in storage will diminish to zero (at a new reduced level of groundwater storage), and inflows will again balance outflows. Thus, the long-term source of water to discharging wells becomes a change in the amount of water entering or leaving the system. The time that is required to bring a groundwater system into equilibrium is a function of the characteristics of the aquifer system, such as permeability, thickness, distance to hydrologic boundaries, and the placement of pumping wells. In summary, natural recharge is a critical element for understanding the water balance, an important parameter in many computer-model simulations of aquifer systems, and is fundamental to understanding contaminant transport from the land surface. All of these aspects may factor into an analysis of the sustainability of a groundwater system. An estimate of natural recharge, by itself, however, should not be used to determine the amount of ground water that can be withdrawn on a sustained basis. The quantity of ground water available for use depends more upon how the changes in inflow and outflow that result from withdrawals affect the surrounding environment and the acceptable tradeoff between groundwater use and these changes. Achieving this tradeoff in the long term is a central theme in the evolving concept of sustainability (Alley and others, 1999; Alley and Leake, 2004).

A Review of Beaver–Salmonid Relationships and History of Management Actions in the Western Great Lakes (USA) Region

“…Glacial erosion and deposition resulted in diverse landforms throughout the WGL region that differ in their ability to hold and transport water (Neff et al. ), and this heterogeneous composition makes it difficult to extrapolate the results of beaver–salmonid studies from one area to another. The manner in which beaver dams may influence lateral and longitudinal flow pathways will likely differ between surficial materials, although this topic remains largely unexplored within the region.…”

Thermal transport modelling in a fully integrated surface/subsurface framework

“…The surface boundary conditions include a constant head boundary for the river inlet, using river stage measurements (Conant, 2001), a critical depth outflow boundary at the river outlet and a prescribed mean monthly rainfall rate applied to the surface. This rate corresponds to the average for the month of July at the field site (Neff et al, 2005). All other boundaries are considered no flow, reflecting the general direction of flow perpendicular to the river.…”

“…About 74 mm of rainfall occurred during the July simulation period based on data collected at Barrie, Ontario (Environment Canada, 2008). The overall recharge rate for the region is estimated at 21 cm year 1 (Neff et al, 2005).…”

Constraining groundwater discharge in a large watershed: Integrated isotopic, hydraulic, and thermal data from the Canadian shield

“…Groundwater recharge, base flow and other important watershed characteristics are often estimated from hydrograph separation [ Rorabaugh , 1964; Moore , 1992; Rutledge and Daniel , 1994; Mau and Winter , 1997; Neff et al , 2005; Risser et al , 2005, 2009]. Hydrograph or base flow methods are only applicable to gauged and unregulated watersheds with substantial groundwater discharge [ Fetter , 2001].…”