Chapter OneChapter OneHydrologic PrinciplesHydrologic Principles

Flashlight and globe

Figure 1-1

Some symbols

Figure 1-2b

The Drainage Divide

Figure 1-2c

The Water Balance

• Conservation of Mass with Storage. • Consider a watershed. We’d like to know,

over the course of one month, how much water got added to the watershed, i.e. how much water got stored in it.

• We might care because we’re using that stored surface water for a water supply, or we might be worried that all that excess water will cause a flood.

• One way of describing this would just be to add up all the things we can think of that add water to the system, and then subtract all the things that we can think of that remove water from the system. The difference would be the change in Storage:

• Inputs:• P = precipitation• I = inflow • G = groundwater flow (could be an input, could be an output)• • Outputs:• E = evaporation• T = transpiration (these are commonly combined to make ET = E + T)• R = surface runoff

Some Examples

Figure 1-5a

Figure 1-5b

Seasonal Rainfall

Figure 1-7

Figure E1-3b

A Hyetograph

Figure 1-8

Figure 1-9

Thiessen Figure E1-4a

Thiessen Figure E1-4c

Thiessen Figure E1-4b

Table E1-4

NEXRAD Rainfall Intensity 5 min samples Figure 1-10

Components of a Direct Runoff Hydrograph Figure 1-11

http://en.wikipedia.org/wiki/Detention_basin

Effects of watershed shape and imperviousness Figure 1-12

Figure 1-14

http://nh.water.usgs.gov/gauge_station/3_howusgs.htm

Figure E1-5

Table E1-5

Figure 1-13

Figure 1-19

Use this for broad shallow bodies of water, e.g. lakes, reservoirs

Table 1-5

Figure 1-21

Horton’s Infiltration Model for soil capacity

Figure E1-8

Figure for Example 1-8 In this example I will compare ahistogram estimate to an exact calculation.

Figure 1-22

index

Streams flow even when there is no rain recently. The water is from base (return) flow.

Figure E1-9

Figure for Phi Index problem E 1-9