2. Chapter 3: Surface Water Hydrology
What is Surface Water Hydrology?
Watersheds
Overland Flow
Rivers
Lakes
Sediment Transport and Deposition
Water Measurement
Flood Events
3. Figure 3.1 Leonardo da Vinci was fascinated by the similarities between the
organization of rivers on the surface of the Earth and the human circulatory
system.
4. What is Surface Water Hydrology?
The study of moving water found in rivers, open channels,
lakes, and runoff across the open land surface
Important for transportation, irrigation, water supply,
hydropower, etc.
Related topics:
Ground water (below the surface)
Marine water (in the oceans)
Icecaps and glaciers
5. Watersheds
The total land area that drains to a common point.
Also called a river basin, drainage basin, or catchment
The watershed is delineated by finding the watershed
divide, or ridge, that separates the watershed from its
neighbors
9. Figure 3.5 The Mississippi River is the third largest drainage basin in the
world, exceeded in size only by the watersheds of the Amazon River in South
America and the Zaire River in Africa.
12. Topographic Maps:
Used to show slope, elevation, distance, and physical features
Scale:
Used to relate the distance on the map to the true distance.
1 map inch = 12,000 true inches = 2000 true feet
Contour Line:
Used to show points of similar elevation.
1000 foot contour line is a constant elevation above sea level
Contour Interval:
The distance between contour lines. A 20 foot contour interval has contours
every 20 feet, i.e., 980, 1000, 1020, etc.
Slope:
The steepness of the ground
A 1% slope is where the surface drops 1 foot every 100 feet.
Aspect:
The direction that the slope faces, North, South, East, West, etc.
13. Three Simple Rules
Surface water generally flows at right angles
(perpendicular) across contour lines
Ridges are indicated by the highest elevation contour
line
Drainages are indicated by contour lines pointing
downstream
16. Overland Flow
Rain falls onto vegetation, and then to the
ground.
Interception is lost in the vegetation
Throughfall makes it to the ground
Stemflow runs down the vegetation
Water reaching the ground can:
Accumulate in depressions
Soak into the ground (infiltration)
Flow across the surface as overland flow
17. Rivers
Components of a River
Headwaters: the source of the river
Tributaries: smaller streams that combine at a
confluence
Upstream vs. Downstream: related to the flow
direction
Thalveg: Main part of river channel
Hyporheic Zone: Shallow ground-water flow below the
river bed
18. River Morphology:
Young, “V” shaped valleys
Older, “U” shaped valleys
Oldest, meandering channels with oxbow lakes
Braided channels with lots of sediment
Channels are choked with sediments
Below glacial terrain
In wetlands where there is very low gradient (slope)
20. Types of Rivers
Ephemeral: flows only during storms
Intermittent: flows seasonally
Losing stream: loses flow to groundwater
Gaining stream: gains water from the subsurface
Gradient: the slope or fall of the river, usually
decreases as the river gets larger.
21. Figure 3.6 Cross section of a gaining (or “effluent”) stream, common in
humid regions, and a losing (or “influent”) stream, often found in arid or
semiarid locations.
23. Lakes
Any body of water (other than an ocean) that is of
reasonable size, impounds water, and moves very slowly
Types of lakes:
cirques: formed in mountains by glaciers
pluvial: formed in deserts
kettles: formed by buried glacial ice that melted
Lake productivity
oligotrophic: very low productivity, clear
eutrophic: very high productivity, green
24. Ecologic Zones
littoral: along the shoreline
limnetic: near the surface in the deeper parts
profundal: near the bottom in the deeper parts
Thermal Cycles
epiliminion: near the surface, warm in summer
hypolimnion: near the bottom, cold in summer
thermocline: boundary between epi- and hypolimnion
lake turnover: in fall when epi- and hypolimnion mix
Seiche:
Wind driven water level fluctuations
27. Sediment Transport and Deposition
This refers to soil carried by water and then deposited in
low energy environments.
The heavy sediments (sands) fall out along the river banks,
forming levees
Finer materials (clays and silts) fall out in flood plains
Yazoo rivers parallel the main river
A delta forms where the sediment chokes the main channel
- often in braided rivers.
28. Velocity
High energy streams have high velocities
Higher velocities can carry more, and larger particles
Sorting occurs when large particles are left behind, and small
particles are carried away
Sediment Load
The total material carried, composed of:
Suspended load: fine materials carried as particles
Dissolved load: materials that are in solution
Bedload: larger materials carried along the bottom
Sediment Yield: The load per unit area
29. Figure 3.11 Steep gradients and high water velocity are great combinations
for moving boulders, sediment, and kayakers.
30. Water Measurement
Rational Formula
Q = C i A
Q is the peak runoff rate, cfs
C is the runoff coefficient
Urban areas, C = 0.9
Industrial areas, C = 0.8
Residential areas, C = 0.6
Forested areas, C = 0.1
i is the rainfall intensity, in/hr
A is the watershed area, acres
31. River Discharge
Discharge is the flow of water
Measured in units of cubic feet per minute, or cfs
The metric equivalent is liters per second, or Lps
We find the discharge, Q, by taking the product of the
velocity, v, and the area, A:
Q = V A
Example, if the width of the channel is ten feet, the depth is
one foot, and the velocity is two feet per second, then
A = 10 ft x 1 ft = 10 ft2
Q = 2 ft/s x 10 ft2 = 20 cfs
32. Figure 3.10 One cubic foot per second, or cfs (or one cubic meter per
second, or cms) is equivalent to one cubic foot (or meter) of water flowing past
a given point in a one-second time interval.
33. The water velocity is found using a flowmeter, which
looks like an anemometer:
34. Figure 3.13 The hydrograph of a river can look similar to this example after
a brief but intense rainfall event.
35. To make things easy, we use a staff gage (or
ruler) to measure the river stage (how high the
river is.
We use a rating curve to relate the discharge to
the river stage.
36. Water Storage in Lakes and Reservoirs
We normally measure large volumes of water in units of
Acre-Feet
1 acre-foot is the volume of water that covers one acre to a depth
of one foot
Lake Lanier, when full, has 2,000,000 acre-feet of water. It
covers 40,000 acres with an average depth of 50 feet.
We keep track of the volume using the stage-capacity
curve:
The storage goes down as the water level, or stage, goes down
37.
38. Flood Events
Flood frequency:
the likelihood that a large flood will happen
100-year flood:
flood that is exceeded - on average - once every 100 years, the
probability in 1 year is 1/100 = 1 %
10-year flood:
probability = 10 %
Mean annual flood:
exceeded once every two years, probability = 50%
39. Figure 3.15 Flood damage can be predicted based on the intensity of a
storm and the topography of a region.
40. Extreme Events
Probable Maximum Precipitation (PMP)
The most extreme rainfall possible
Used for estimating the effects of extreme weather
Probable Maximum Flood (PMF)
The most extreme flood possible
Used for estimating maximum extent of flooding
41. GIS Mapping
Geographic Information Systems (GIS):
Used to organize spatial information
Various properties are stored in the computer
GIS layers include topography, soils, hydrography,
vegetation, land use, etc.
42. Figure 3.16 A GIS map display showing the schools in a town. Notice that a
query of Elmar High School was made, and the corresponding attribute data
and digital image are shown.
43. Figure 3.17 Streams, lakes and medical facilities are added to the original
map display.
44. Figure 3.19 With the Q100 layer added to the map display, it is easy to see
that Edwards Elementary is the only school in the 100-year floodplain.
45. Quiz 3
If the Oconee River is flowing at a rate of 1000 ft3/s, how long would it take to fill this
room?
Use the tape measure provided to measure the length, width, and height of the room, and
calculate the volume, in cubic feet. [Use L = 60’, W = 100’, H = 12’]
Calculate the time by dividing the volume (ft3) by the flow rate (ft3/s), giving you the time, in
seconds.
Delineate (draw the boundary around) the Oconee River Watershed using the map
found at: www.hydrology.uga.edu/Georgia.pdf
True - False Questions:
[T / F] Overland flow is more likely in forested watersheds because it rains harder there
[T / F] Urban areas have higher runoff peaks than agricultural areas
[T / F] Sand is easier for rivers to carry than clays
[T / F] A 100-year flood has a 1 percent chance of happening in any one year
[T / F] The Probable Maximum Precipitation is the largest observed rain in a year.
If Athens is located 300 river miles from the coast, and the river flows at a rate of 3 miles
per hour, how long will it take the water to reach the ocean?
For the previous problem, what would happen if there is a lake between Athens and the
coast?
