Forest Water Resources (FNR4343)
Spring 2014
Midterm Exam Study Guide
Lecture 1 - Introduction
- Water properties
o Temperature vs. density of water
o Capillarity (surface tension and adhesion)
o Solvent/polarity
o Relationship between temperature and water-holding capacity of air
o Latent heat capacity (phase transitions)
o pH of rainfall (what is acid rain?)
Lecture 2 – Watersheds and the Hydrologic Cycle
- Hydrologic cycle
o Sources
o Reservoirs
o Drivers
o Is net rainfall (rain – ET) positive over land or sea?
- Hydrologic cycle in Florida
o What makes it unique?
o How much rain do we get?
o What is a confining unit?
- Water Balance
o Sources
o Sinks
o Storage
- Water Budget Equation
o Typical flatwood water budget
o How is a flatwoods water budget different from other land uses
(qualitatively)?
o Units for comparison are m/yr for all components – what does this mean?
o What do we infer from unbalanced water budgets?
- Watershed terminology
o Size classes
o Hierarchical nesting
- Delineating watersheds
o Process
o What does the resulting watershed polygon represent?
o Why delineate watersheds?
- What is a paired watershed, and why use them?
Lecture 3 – Precipitation
- Rainfall and forest cover/type
o Rainfall threshold below which forests don’t grow?
-
-
-
-
-
-
-
-
o Three precipitation factors that control forest type
Water Vapor
o Relative humidity (RH) – define.
o Saturation vapor pressure
o Condensation occurs when Vaporactual ≥ Vapormax
o Cooling to Condensation vs. RH
o Dry Adiabatic Lapse Rate – what is this?
o Why does the actual lapse rate not typically follow the dry lapse rate?
o What is the tropopause?
Convective Precipitation
o Condensation elevation
o Latent heat liberation (what are the effects?)
o What energy fuels convection in a thunderstorm?
Radiation Budget
o How much total energy lost via latent heat?
o Albedo?
o Land vs. Water heating (heat capacity differences lead to differential
heating)
Orographic Precipitation
o Mountain range effects
o Rain shadows
Frontal Precipitation
o Cold fronts
o Warm fronts
Cloud drip
Snowfall/Sleet/Hail
Why is Florida so Wet?
Direct Rainfall measurement techniques
o Gauges
 How do they work?
 Measurement errors
 Interpolation methods
o Tipping Buckets
 How do they work?
Spatial variability
Indirect rainfall measurement techniques
o NexRad
o Microwaves
Sizing a culvert
o Precipitation records (annual maximum series)
o Recurrence intervals
o Q = CIA
o After estimating maximum flow, determine the pipe diameter to allow that
flow through
Lecture 4 – Evapotranspiration
- What is a typical ET rate from a Florida native ecosystem? Pine stand? Parking
lot? Crop land?
- Vaporization process based on saturation vapor pressure gradient (psat - pactual)
- Temperature effects on the vapor pressure gradient
- PET vs AET
- Requirements for ET: Energy, Water, Wind and Vapor Pressure Gradient
- Rnet = Rtot * (1-)
- Albedo values ()
- Multiple methods for estimating ET
o Simple temperature based methods
o Complex methods (e.g., Penman) based on radiation, wind, saturation
deficit
o Be able to look at a temperature-vapor pressure chart (e.g., slide 7, lecture
3) and determine the saturation temperature (dew point) of an air mass if
given the current temperature and relative humidity
- Energy Budget Equation (Rnet = E + H + G)
o  = latent energy of vaporization = 586 cal/g
o E = evaporative flux (in grams of water per time)
o H = sensible heat flux
o G = soil heat flux
- White method (diel variation)
o What is it and how does it work?
o What is the specific yield and why is it important?
- Bowen Ratio
o What would happen to the Bowen Ratio in a parking lot vs. a forest?
o What is expected to happen to the Bowen Ratio with stand age?
- Order of ET processes
o Interception rates/losses
o Transpiration
 What are the implications of forest management on transpiration?
 What is the cohesion-tension theory?
 Why can trees raise water in their xylem higher than the theoretical
maximum for water in a large tube? What is an embolism?
o Surface water evaporation
o Soil water evaporation
 Rooting depth effects
 Cover effects
- Discuss the effect of afforestation on landscape ET, and implications for other
attributes of the hydrologic cycle
o What is the difference between natural and plantation pine stands with
regard to ET?
o Discuss the environmental trade-offs implied by this difference (C
sequestration, bioenergy)
-
What limits soil evaporation from unsaturated soils? How do plants overcome
this limitation? How does the ability to overcome this limitation vary among
plant types?
Lecture 5 – Streamflow
- What is a hydrograph? What are the major aspects of a hydrograph?
o What is the time domain of surface runoff reaching a stream? Surface
groundwater flows (interflow)? Deep groundwater flows?
- Flow vs. Rainfall Intensity
- Variable source area concept
o Define and explain the prediction this concept makes about the amount of
runoff that occurs after a period of heavy rainfall? Drought? What factors
predict which areas of the watershed you would expect to be “variable”
source areas?
- How does infiltration vary among landscapes
o Characteristic peak flow from each land use type
o Characteristic time of concentration for each land use type
- What is the role and importance of landscape water storage?
o Where is the storage in natural landscapes? What about urbanized
landscapes?
- What happens to streamflow when forests are harvested?
o What factors control this response?
o How long would you expect this response to persist?
- Flow recurrence series and annual flow probabilities
- Q = CIA (Rational Method) for PEAKFLOW estimation
- Measuring streamflow
o Flow (Q) = V *A
 V = velocity (where?)
 A = cross-sectional area
o What are stage-discharge equations and why make them?
- Manning’s Equation for flow estimation without a rating equation
o Manning’s Number (n) would be given to you
o Area (A), hydraulic radius (r), and hydraulic gradient (s = H/L) would
need to be calculated
Lecture 6 – Groundwater
- What and where is the Floridan aquifer?
- What does it mean to be unconfined and where is that an issue?
- What is the effect of extended pumping above the aquifer transmissivities? What
areas of the Floridan are most hard hit?
o What is a cone of depression?
o What are the implications of this process on springs, streams, wetlands
and additional regional pumping?
o What is the effect of Gainesville’s “cone” on regional groundwater quality
concerns?
-
-
What is a potentiometric surface? What is the elevation of the potentiometric
surface compared with the land surface at a spring?
What are some relevant questions about the fate and transport of contaminants to
the groundwater where a confining layer exists? Where one is absent?
What is the Hawthorn Formation?
What is an artesian spring or well?
Darcys Law
o Q = K A H/L
o Q = flow
o K = saturated hydraulic conductivity (units?)
o A = cross-sectional area (which area?)
o H = potential difference between two locations (units?)
o L = path length of water flow (units? Which flow path?)
o Water flows from “high” potential to “low” potential, which can be uphill
Darcys law can be used for vertical AND lateral seepage questions
o What is the cross-sectional area for each?
o What is the L for each?
Lecture 7 – Soil Water Processes
- Infiltration process
o Spatial and temporal variability
- Capillary rise (function of texture)
o What is matrix potential?
o What is affect on infiltration dynamics in unsaturated soils?
o What causes it?
- Infiltration equations fp = fc + (fo – fc) e-kt
o fp = current infiltration capacity
o fc = equilibrium infiltration capacity
o fo = initial infiltration capacity
o k = a constant describing the rate of change from initial to saturated
behavior
o t = time
- How is overland flow generated? How does the dynamics of infiltration with
time affect how much rainfall of a given amount will become runoff?
- Texture effects on infiltration
- Soil structural effects on infiltration
- What is hydrophobicity, and under what circumstances does it develop?
- Physical energy to remove soil structure from falling raindrops
o What is the role of the forest floor in absorbing that energy?
- Changes in infiltration capacity due to compaction
- Infiltration capacity effects of land use
- Measuring infiltration
- Change in storage (S) = Storageend – Storagestart
o Equivalent Surface Depth. (ESD) = Volumetric Water Content * Soil
Depth; at Saturation, ESD = Porosity * Soil Depth
o Porosity and Bulk Density relationship
o Porosity = % of soil volume that is voids
o Moisture content = % of voids that are filled with water (100% @
saturation)
o How do you measure moisture content? Bulk density?
o What is specific yield?