1. FORY-7550 Watershed Hydrology

2. Introduction Where in the world gets least and most rains?
Cherrapunji – India gets on average meters of rain/yr
Atacama Desert in Chili gets < 1mm per year
(there was a period of 14 years without a drop of rain)
Alabama gets about 4 times more rain than my hometown
No drought problem in my hometown, yet AL is in drought every 3 to 7 years… WHY?
Can humans change the hydrologic cycle? How?
If you can predict with precision how much it will rain can you predict how much will the river rise, will it flood?
How should we operate a reservoir for optimum water use: e.g. flood control, irrigation, recreational use, electric generation, etc.

3. Introduction Where does water come from/go? What does water carry?
How does water affect forests?
How do forests affect water?
How do we affect both?

4. What is Hydrology? Literally means the science of water
It is the study of hydrologic cycle, which is the endless circulation of water between earth and its atmosphere
It embraces such a large and diversified field that no one can study it all.
The broad science of hydrology called “hydroscience” can be broken into many disciplines based on bodies of water, land use conditions and interdisciplines of water and land

5. Testing your knowledge – True or False
Water contracts when it freezes.
Water has a high surface tension.
Condensation is water coming out of the air.
Rainwater is the purest form of water.
It takes more energy to heat water at room temperature to 100 °C than it does to change 100 °C water to steam.
Sea water is slightly basic, natural rain water is ~100x more acidic.
Raindrops are tear-shaped.

6. Testing your knowledge – True or False
Water contracts when it freezes (F)
Water shrinks as it cools until 4 °C when the trend reverses
Ice is lighter than water. Imagine the implications if this wasn’t true
Water has a high surface tension (T)
Water has the highest surface tension among common liquids (Hg is higher)
Capillary rise is based on surface tension
How far water rises in a tube.
Has major implications for plant-water interactions

7. Testing your knowledge – True or False
Condensation is water coming out of the air (T)
The quantity of water that can reside in vapor form in the air changes with temperature
Fundamental to the hydrologic cycle
If all water in the atmosphere were to condense suddenly, it would yield only 1” of water over the globe
Rainwater is the purest form of water (F)
Rain contains impurities: H+, carbonates (hardness), nutrients (N, P, Ca, K…), salts, pollutants, dust, viruses
A key component of forest nutrition

8. Testing your knowledge – True or False
It takes more energy to heat water at room temperature to 100 °C than it does to change 100 °C water to steam (F)
Water has 3 phases at normal temperatures
~ 5.4 x MORE energy is required to convert water at 100 °C to steam at 100 °C than to raise the temperature of liquid water from 0 °C to 100 °C
Major implications for the energy budgets of ecosystems
Latent Heat (extremely important)

9. Testing your knowledge – True or False
Sea water is slightly basic, natural rain water is ~100x more acidic (T)
The sea has pH ~ 8
Deionized water has pH = 7
Rainwater (normally) has pH ~ 5.5 (presence of CO2 creates carbonic acid)
Rainwater (acid rain) may have pH ~ 4
Raindrops are Round
Water has high surface tension
Round in the absence of differential pressure, but shaped by contact with other objects such as air, faucet

10. Disciplines of Hydrology
Based on water body:
Potamology: Study of surface streams
Limnology: Study of lakes and ponds
Cryology: Study of snow and ice. Also called snow hydrology
Oceanography: Study of oceans
Glaciology: Study of glaciers
Hydrometeorology: Application of meteorology to hydrological problems
Hydrogeology: Study of groundwater (groundwater hydrology)
Hydrometry: Science of Water measurements

11. Disciplines of Hydrology
Based on Land Use Conditions:
Rangeland Hydrology: Rangelands are natural grasslands, savanas, shrublands, tundra, etc. Typically short and broad-leafed plants.
Agricultural Hydrology: Water use for agg irrigation and livestock is the greatest single use in U.S. (~42%)
Forest Hydrology
Urban Hydrology
Wetland Hydrology
Desert Hydrology

12. Disciplines of Hydrology
Based on Interdisciplinary Studies:
Geomorphology: concerned with landforms and drainage characteristics created by running water and other physical processes
Paleohydrology: Study of hydrologic conditions in ancient times. Investigation of tree rings (dendrohydrology), glacial fluctuations, fossils, pollen depositions in bogs (palynology), sediment cores in deep seas and lakes, etc.
Engineering Hydrology: study of hydrologic characteristics of a watershed or drainage system required to solve engineering problems
Watershed Management
Hydrobiology: topics related to aquatic plants
Others: Ecohydrology, medical hydrology, ….

13. Forest Hydrology The study of the interface between forest and water
1/3 of the total land surface on earth is forest or woodland (FAO 2005 – for year 2000)
60% of total runoff is generated from forested lands
Most of our drinking water comes from forested areas
Activities in those areas affects quality and quantity of water
Do forest decrease water?
Do they help or worsen climate change?
Kittredge (1948) first suggested the name “forest hydrology”

14. Watershed Hydrology
Study of water as it interacts with various parts of a watershed, including the land, the sea and the sky

15. History of Hydrology
From ancient times many speculated about the circulation of water. Much of this speculation was scientifically unsound
Same questions and issues are prevalent today
How much water is there?
Where is the water coming from?
Where is it going?
What is the quality of water, how can we control it?
What should we do when we have too much or too little
Early thinkers and philosophers did not understand the 3 basic hydrologic principles?
Conservation of mass
Evaporation and condensation
infiltration

16. History of Hydrology
They were worried about how water gets up to mountains and flows down to sea
They could not see rainfall as a sufficient source for streamflow
Underground reservoirs beneath the mountains are hypothesized.
Water was believed to be pushed up by vacuum forces
These reservoirs were replenished by sea

17. History of Hydrology
Vitrivius (1st century BC) first recognized the infiltration processes
Leonardo da Vinci made the first systematic studies of velocity distributions in streams. He likely was the first to provide a complete description of the hydrologic cycle
18th and 19th centuries: hydraulic experiments flourished
Until 1930 hydrology remained a science full of empiricism, qualitative descriptions and little understanding of physical processes
All these experience and study have converged to form the concept of “hydrologic cycle”