B.F. Bachelor of Forestry Forest Hydrology and Watershed Management 1 — Questions and Answers
Question 1: What is 'interflow' (also called subsurface stormflow) in a forested watershed?
- Water that moves laterally through the soil above an impeding layer and discharges into a stream during or shortly after rainfall (Correct answer)
- Water that evaporates directly from the soil surface during dry periods
- Deep percolation of water into bedrock aquifers
- The portion of precipitation intercepted by the forest canopy
Correct answer: Water that moves laterally through the soil above an impeding layer and discharges into a stream during or shortly after rainfall
Interflow is lateral water movement through the upper soil horizons, above a less permeable layer, that reaches streams relatively quickly after rain — faster than groundwater baseflow but slower than overland flow.
Question 2: Which process describes the uptake of soil water by tree roots and its subsequent release as vapor through leaf stomata?
- Infiltration
- Transpiration (Correct answer)
- Percolation
- Capillary rise
Correct answer: Transpiration
Transpiration is the biological process by which plants absorb water through roots and release it as water vapor through stomata; it is a major pathway of water loss from forested watersheds.
Question 3: What does the term 'evapotranspiration' (ET) represent in a watershed water balance?
- The combined water loss through soil evaporation and plant transpiration (Correct answer)
- The total volume of water stored in the soil at field capacity
- Runoff generated exclusively by snowmelt events
- Streamflow measured at the watershed outlet during dry seasons
Correct answer: The combined water loss through soil evaporation and plant transpiration
Evapotranspiration combines evaporation from soil and water surfaces with transpiration from vegetation; together these represent the dominant water output from most forested watersheds.
Question 4: In the variable source area concept, where does overland flow (saturation excess runoff) most commonly originate in a forested watershed?
- From ridge tops and upper slopes where soils are thin
- From saturated areas near streams, seeps, and concave hollows (Correct answer)
- Uniformly across the entire watershed surface
- Only from recently harvested clear-cut areas
Correct answer: From saturated areas near streams, seeps, and concave hollows
Saturation excess overland flow occurs where soils become fully saturated; this typically happens first in low-lying riparian zones, topographic hollows, and areas adjacent to streams where the water table is near the surface.
Question 5: What is a 'riparian buffer strip' and why is it important in watershed management?
- A planted windbreak along ridge lines to reduce wind erosion
- A vegetated zone along stream banks that filters runoff, stabilizes banks, and protects water quality (Correct answer)
- A gravel-lined channel designed to increase stream velocity
- A cleared strip of land used to create firebreaks near waterways
Correct answer: A vegetated zone along stream banks that filters runoff, stabilizes banks, and protects water quality
A riparian buffer strip is a band of native vegetation maintained along streams; it traps sediment and nutrients from upslope runoff, provides bank stability through root reinforcement, moderates stream temperature with shade, and supports aquatic habitat.
Question 6: What is the primary hydrological effect of forest harvesting (clear-cutting) on annual water yield from a watershed?
- Water yield decreases because exposed soil absorbs more rain
- Water yield increases because transpiration losses are greatly reduced (Correct answer)
- Water yield remains unchanged because precipitation is unaffected
- Water yield decreases due to increased surface albedo after harvest
Correct answer: Water yield increases because transpiration losses are greatly reduced
Removing forest vegetation eliminates transpiration, which is typically the largest single water output; with less water leaving via plants, more water becomes streamflow, causing annual water yield to increase — a well-documented finding from paired watershed experiments worldwide.
B.F. Bachelor of Forestry Forest Hydrology and Watershed Management 1
What is 'interflow' (also called subsurface stormflow) in a forested watershed?