Groundwater Flow: Blackboard Example

U.S. Water Supply / Water Budget Depends on rates of precip., evap., stream flow, and subsurface flow

Developing a Regional Water Budget Depends on local precip. and evaporation scenario – Pacific Northwest vs. Desert Southwest vs. Florida Peninsula Problem: Timing is critical – can’t store all of the mean annual runoff. Example: Snowpack in British Columbia – Spring of 1998.

Groundwater Supply 20% of U.S. consumptive water withdrawls Needs protection, because residence times in aquifers can be hundreds to thousands of years Groundwater seepage provides baseflow to streams Groundwater mining – if withdrawl exceeds natural inflow, groundwater can be considered a non-renewable resource

Groundwater Depletion – Ogallala Aquifer Gravel and sandstone aquifer extending from So. Dakota to Texas In places, groundwater withdrawal is 20x the natural recharge rate Well-water levels have dropped 30-60 meters in places due to long-term irrigation Sustainability? As water table level drops, yields decrease and it becomes more costly to pump.

Water Supply - De$alination Thermal Distillation - Process of taking in seawater, evaporating, moving, condensing, and collecting. Reverse Osmosis- Use semi-permeable membranes and pressure to separate salts from water – less energy intensive than thermal distillation. Largest desal plant in US = Tampa Bay.