Chapter 1 part2 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:
- the land it traverses,
- 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.
Water over the earth is
conserved
Area in % of water surfaces and continents
- Water surfaces: 71%
- Continents: 29%
Area in % of deserts and forests of continents
- Deserts: 35%
- Forests: 30%
river basin is also called
- watershed
- catchment
- drainage basin
A river basin
is the area contributing to the discharge at a particular river cross-section.
water balance equation
water balance equation means
precipitation - evapotranspiration - river discharge = change of storage with time
Precipitation and evapotranspiration are usually measured in
mm/d
river discharge is usually measured in
m3/s
water balance is often applied to a
river basin
The size of the catchment increases if
the point selected as outlet moves downstream
the water balance equation is applicable if
If no water moves across the catchment boundary indicated by the broken line
percentage of water in world oceans
97% of water
percent of polar ice (water and fresh water)
% of water = 2.14
% of fresh water = 77.6
percent of atmospheric water (% of water & fresh water)
% of water= 0.001
% of fresh water= 0.03%
percent of fresh lakes (fresh water)
0.335%
a time that the amount of water in store is expected not to vary much for each successive year is known as
hydrologic years or as water years
The storage equation is especially useful to
study the effect of a change in the hydrologic cycle
The figure shows
The catchment area increases as the control point moves down stream
The topographic divide between two watersheds is usually taken as the
boundary of the catchment, the water divide
the figure shows that
the topographic divide applies to surface runoff, but may not necessarily coincide with the boundary for groundwater flow, the phreatic divide
(water balance due to human interaction)
Between two high areas is a
water shed
The water diversion cycle including ………………………….. results in the following water balance equation
human interference
The water diversion cycle including human interference results in the following water balance equation
Runoff Coefficient
the percentage of rainfall that comes to runoff
what does each symbol mean?
P = precipitation on the ground surface
E = evapotranspiration from the ground surface
A = net water consumption due to water use
R = runoff from land to ocean
Is = intake of water from surface runoff
Ig = intake of groundwater
D = drainage of waste water
