12:166, Zhang

Spring, 2002

Lecture on

HYDROLOGIC CYCLE AND EQUATION

· Water in Motion: Hydrologic Cycle

Evaporation (E) and Transpiration or Evapotranspiration (ET)

Condensation

Precipitation (P)

Runoff (R)

Infiltration (I)

Groundwater Flow (G)

· Water on the Earth: Global Water Distribution

· Water Balance: Hydrologic Equation

Q_in – Q_out = DS

· Hydrologic Equation for a Surface Water Body, e.g., a lake

P + OF_in + RO_in + GW_in + Q_import - ET - GW_out - RO_out - Q_export = DS

· Hydrologic Equation for a Drainage Basin or Watershed

P + GW_in + Q_import – ET - GW_out - RO_out - Q_export = DS

· Hydrologic Equation for a Groundwater basin or System

R + GW_in + Q_import - ET - GW_out - Q_export = DS

Note: It is important to identify your system boundaries when working on a hydrologic eq.

· Water in the Air: Evaporation (E) and Evapotranspiration (ET)

Measuring Evaporation

Class A Pan and Class A Pan Coefficient

Lake Evaporation nomograph

Potential Evapotranspiration (ET_P)

Actural Evapotranspiration (ET_A)

· Falling Water: Precipitation (P)

Computing Average Precipitation

Arithmetic Mean

Thiessen Method

Contour Map or Isohyet

Kriging or BLUE (a geostatistical method)

· Percolating Water: Infiltration

Horton Infiltration Equation: f_p = f_c + (f_o - f_c) e^-kt

· Groundwater: The main subject of this class

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Reading: Chapter 2 of the textbook and the web site:

http://observe.ivv.nasa.gov/nasa/earth/hydrocycle/hydro1.html

Homework: Problems 8 and 14 at the end of Chapter 1 (p.22-23) and the problem on the back

of this page Due on Mon., Feb. 4.

12:166, Zhang

Spring, 2002

Homework # 1

Due on Mon., Feb. 4

1. The Big Spring basin is a groundwater basin (Figure 1 from Zhang et al., 1996). It has a recharge area of 267 km². About 85 percent of groundwater discharged from the basin exits the base of the Galena aquifer through Big Spring. The spring discharges at an average rate of 43.8 cfs (cubic feet per second) or 1.24 m³/s from the Galena limestone aquifer. The mean annual precipitation is about 84 cm.

· Write down a hydrologic equation for the Galena limestone aquifer with only non-zero terms.

· Can you determine the net recharge to the aquifer? What is it? List all your assumptions.