GEOG101: Physical Geography

Lecture 11: Monday, March 2, 2009

Topics
1. The Hydrologic Cycle
2. Soil-Water-Budget Concept
3. Groundwater Resources
4. Our Water Supply

The Hydrologic Cycle
• Read Figure 9.1, p. 247 on the hydrological cycle to understand the following:
      Sketch and explain a simplified model of the complex flows of water on Earth -- the hydrologic cycle:
      Output: Evaporation (ocean)--86%; Evaporation + Transpiration (land) [or called Evapotransporation]-- 14%
      Input: precipitation (ocean)--78%; precipitation (land)--22%
      So you see a imbalanced equation between ocean evaporation and precipitation in the ocean and on the land. What happened to those extra 9% evaporation in the ocean and extra 8% precipitation on land?
      It's because of the atmospheric advection of water vapor: 20% of water vapor from ocean precipitation advected to land and precipitates there; 12% of water vapor from land evaporation and transpiration advected to the ocean and precipitates there.
      The extra precipitation on land return to the ocean through surface runoff and through groundwater circulation;
      Groundwater consitutue the the largest potential freshwater source in the hydrologic cycle, but it has a much larger resident time than the surface water.

• What are the possible routes that a raindrop may take on its way to and into the soil surface? (Read Fig. 9.2, page 248)
      Interception:The process of precipitation striking vegetation or other groundcover.
      Throughfall: Precipitation that falls directly to the ground, coupled with drips onto the ground from vegetation.
      Stem flow: intercepted water that drains across plant leaves and down plant stems. It can represent an important moisture route to the surface.
       Water reaches the subsurface through infiltration, or penetration of the soil surface. It then permeates soil or rock through vertical movement called percolation .

Soil-Water-Budget Concept
• A water balance can be established for any area of Earth's surface by calculating the total precipitation input and the total of various outputs.
• Read Fig. 9.3, page 249, to understand the basic input and output of water balance equation:

PRECIP = ACTET + SURPL +/- delta STRGE
      PRECIP: the total precipitation including rain, sleet, snow, and hail in a specific area within a specific time period;
       Precipitation is measured with the rain guage.
      ACTET: Actual evapotranspiration including evaporation and transpiration. It can be calculated by:
ACTET = POTET - DEFIC , where

         POTET: The potential evaporation and transpiration under optimum conditions
         POTET can be measured by an evaporimeter or lysimeter.
         The POTET demand can be satisfied in three ways: by PRECIP, by moisture stored in the soil, or through artifical irrigation
         DEFIC: If the source of moisture cannot meet the evapotransipration demand, the location would experiences a moisture shortage. This shortage is the defecit.
         You would like to avoid the DEFIC of your body!
      SURPL: If the POTET is satisfied and the soil is full of moisture, the the additional water input becomes surplus (SURPL).
       Suplus water generates most streamflow.
       delta STRGE: A "saving account" of water that receives recharge deposits and provides for utilization withdrawals is called the "soil-moisture storage (delta STRGE)".

      Soil moisture is composed of two categories of water (Fig. 9.8, p. 253):
         Hygroscopic water: water molecules tightly bound to each soil particles that are inaccessible to plants
        If all water remains is the inaccessible water to plants, the soil is at the wilting point
         Capillary water: water held against the pull of gravity in the soil by hydrogen bonds between water moledules
        The amount of water available in soil-moisture storage after water drains from the larger pore spaces is termed the field capacity
         Gravitational water: The water percolates from shallower capillary zone to the deeper ground water zone.

Groundwater Resources
• Read Figs. 9.17, p. 262-263 , understand the following terms:
• Water table: the upper limit of the water that collects in the zone of saturation
• Acquifer and Aquiclude
• Confined and unconfined acquifers; Collapsing aquifers
• permeable water, potentiometric surface, artesian water
• effluent stream, Influent stream, cone of depression, saturated zone

Our Water Supply
• Instream, Nonconsumptive, and consumptive uses of water ( Fig. 9.20, p. 270).
• The High Plains Aquifer is the largest known acquifer in north America. It has been pumped extensively for agricultural use
• Instream uses of water includes Waste dilution, wildlife preservation, and hydroelectric power production
• On a worldwide basis, the majority of water withdrawal occurs for agricultural use.



Please report any problems of this website to Dr. Jiang