Forest Water Resources (FNR4343)

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
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
Orographic Precipitation
o Mountain range effects
o Rain shadows
Frontal Precipitation
o Cold fronts
o Warm fronts
Cloud drip
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
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
- 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
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
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% @
o How do you measure moisture content? Bulk density?
o What is specific yield?