Chapter 1 part2 Flashcards Preview

hydrology > Chapter 1 part2 > Flashcards

Flashcards in Chapter 1 part2 Deck (56)
Loading flashcards...

Define watershed

basin-like landform defined by highpoints and ridgelines that descend into lower elevations and stream valleys.


What happens in the watershed 

carries water "shed" from the land after rain falls and snow melts.

water is channeled into soils, groundwaters, creeks, and streams,

making its way to larger rivers and eventually the sea.


water is affected by

all that it comes in contact with:

  1. the land it traverses,
  2. and the soils through which it travels.


what we do on the land affects

water quality for all communities living downstream.


Hydrologic processes encompass a suite of

space and time scales


thunderstorm space and time scale

space scale: few kilometers or less

time scale: minutes to hours


development of major river basins space and time scale

Space scale: 1,000 - 10,000 km

time scale: millions to tens of millions of years


Within watershed, water exists as

  • precipitation
  • surface water (or runoff)
  • groundwater 
  • evaporation


principle of conservation of mass is applied assuming

watershed is a closed system


the principle of conservation of mass is used to 

track how much water is in storage


What is conservation of mass?

for any closed system, mass is conserved over time


equation of conservation of mass


the following equation is 

conservation of mass


What are the inputs of water into our watershed?

Precipitation and any groundwater flowing in.


What are the outputs of water into our watershed?

Runoff, evaporation and any groundwater flowing out.


The regional water balance equation 


The following equation is for

Regional water balance equation


what does P, GWin, GWout , E, Q and S resemble?

  • P: precipitation
  • GW in: ground water (in)
  • GWout: ground water (out)
  •  E: Evaporation
  • Q: Runoff
  •   S: Storage


What is the equation?

simplification of the regional water balance equation


What happens to water after it rains?

  • water can infiltrate into the ground and replenish our groundwater supply,
  • evaporate, returning to the atmosphere.
  • flows into rivers and streams and discharges into oceans or reservoirs. (runoff) 


What happens to runoff? (starts, flow, .....)

  • starts in streams
  • flows into rivers
  • empties into the ocean


Why is runoff important to a community?

For people to use as a drinking water source, irrigation source, etc.


Why is runoff important to plants and animals?

It keeps them alive and healthy. It provides habitat for aquatic freshwater organisms


Why would estimating the amount of runoff be important for engineers?

For engineering purposes such as flood management, hydropower applications, dam design, water resource/supply management, etc


what would occur if it rains a lot?

There will be a lot of runoff.

If the amount of runoff is too much for a riverbed to carry, then water rises up over the riverbanks and creates a flood.


Water balance equation in terms of rate of change in storage


What does I, R and ΔS/Δt mean?

  • I: inflow in [L3/T]
  • O: outflow in [L3/T]
  • ΔS/Δt : rate of change in storage over a finite time step in [L3/T] of the considered control volume in the system.


The equation can be used when

The equation holds for a specific period of time and may be applied to any given system provided that the boundaries are well defined


other name for the water balance equation

  • Storage Equation
  • Continuity Equation
  • Law of Conservation of Mass


types of water balances

  • the water balance of the earth surface;
  • the water balance of a drainage basin;
  • the water balance of the water diversion cycle (human interference);
  • the water balance of a local area like a city, a forest, or a polder.