CSM Hydrology & Watershed Management 2 — Questions and Answers
Question 1: Which hydrologic process describes the movement of water from the soil surface into the soil profile?
- Percolation
- Infiltration (Correct answer)
- Interflow
- Exfiltration
Correct answer: Infiltration
Infiltration is the process by which water on the ground surface enters the soil, while percolation refers to downward movement through the saturated zone.
Question 2: A watershed with a curve number (CN) of 90 compared to one with CN of 60 will produce:
- Less runoff for the same rainfall event
- More runoff for the same rainfall event (Correct answer)
- The same runoff but with longer time to peak
- More infiltration and less surface flow
Correct answer: More runoff for the same rainfall event
Higher curve numbers indicate less permeable, more developed or compacted land, resulting in greater direct runoff for the same precipitation event.
Question 3: What is the term for the portion of precipitation that eventually reaches a stream channel through shallow subsurface flow?
- Baseflow
- Overland flow
- Interflow (Correct answer)
- Deep percolation
Correct answer: Interflow
Interflow (also called subsurface stormflow or throughflow) moves laterally through the upper soil horizons and contributes to streamflow during and shortly after storms.
Question 4: The rational method formula Q = CiA requires that the storm duration equal the time of concentration because:
- Shorter storms produce higher peak flows
- The entire watershed contributes runoff simultaneously at peak flow (Correct answer)
- Longer storms produce more total runoff volume
- The rational coefficient C changes with storm duration
Correct answer: The entire watershed contributes runoff simultaneously at peak flow
When storm duration equals time of concentration, all parts of the watershed are contributing simultaneously, producing the maximum peak discharge for that rainfall intensity.
Question 5: Which factor most directly reduces the lag time between precipitation and peak streamflow in an urbanized watershed?
- Increased impervious cover and storm sewer networks (Correct answer)
- Increased tree canopy and forest cover
- Construction of detention ponds
- Expansion of riparian buffer zones
Correct answer: Increased impervious cover and storm sewer networks
Impervious surfaces and storm sewers speed overland and channel flow, shortening the time for water to travel from the watershed to the outlet.
Question 6: In the SCS/NRCS runoff curve number method, which antecedent moisture condition (AMC) applies to soils that are close to their wilting point?
- AMC I (dry) (Correct answer)
- AMC II (normal)
- AMC III (wet)
- AMC IV (saturated)
Correct answer: AMC I (dry)
AMC I represents dry antecedent soil moisture conditions near wilting point, which produces the least runoff for a given rainfall event.
Question 7: A stage-discharge relationship (rating curve) for a stream gauging station is developed by:
- Using Manning's equation with assumed roughness values
- Correlating measured water surface elevations with measured streamflow discharges (Correct answer)
- Applying the rational method with local rainfall data
- Calculating the cross-sectional area times average velocity from Manning's n
Correct answer: Correlating measured water surface elevations with measured streamflow discharges
Rating curves are developed empirically by repeatedly measuring both stage (water surface elevation) and discharge at a station over a range of flow conditions.
CSM Hydrology & Watershed Management 2
Which hydrologic process describes the movement of water from the soil surface into the soil profile?