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?