Question Deck 3 Flashcards
Describe the three stages of the runoff cycle.
- Early Stage- rain starts, most intercepted by vegetation and soil with infiltration, no immediate flow into the stream. Some of the intercepted water begins to evaporate from the vegetation.
- Middle Stage- Rain continues to fall, runs off the vegetation and falls to the ground. If coming down steadily, may exceed soil’s infiltration capacity and
begin to fill shallow depressions and accumulate on the surface, begins to move continuously as overland flow/inter-flow toward a watercourse - Late Stage- When the rain stops, overland flow and
inter-flow soon cease, and evaporation removes water
from the wet vegetation and surface puddles. Slowly recedes over time as bank storage
What variables affect runoff, and how might these vary between different watersheds?
- Climate- warm/cold, humid/arid
- Physical characteristics of the watershed- topography, vegetation/soil, geology
- Land Cover Use- urban, agriculture,
What is a storm hydrograph and what factors could influence the shape of that hydrograph?
- Shows the amount of stream-flow at a given time in one stream
- Fluctuates based on precipitation events/patterns and infiltration rates/occurrence
Why does base flow produce a greater volume of stream discharge after a precipitation event compared to discharge prior to that storm event?
- During dry times streams dependent on groundwater/base-flow with low volume
- Precipitation allows water to replenish the ground system and increasing volume with excess water adding to the stream
Why can two precipitation events of a similar magnitude generate different flood responses?
- Antecedent soil measure (wetness of soil before rain) influences amount of infiltration
- Land cover/urbanization greatly influence more runoff
Why are continuous streamflow measurements necessary in hydrology, and what techniques are available for this method?
- Necessary because hydrologic activity actively differs due to precipitation/climate and can prevent disasters.
- Methods- Measure the channel (width/depth) to measure current/historical streamflow
- Find average velocity along strech of river/stream via Manning’s equation
What is the relationship between stage and discharge?
- Gage height (also known as stage) is the height of the water in the stream above a reference point.
- Measure discharge at various stages to get average velocity of stream flow.
What are some of the primary drivers of modern-day hydrologic change?
- Land cover change/urbanization
- Climatic/regional changes
- Both are created by human activity
How does urbanization compare with other types of land use changes in terms of its hydrologic impact?
- Most surfaces are impermeable and have fast runoff/little infiltration
- Less lag time/flashy storm hydrographs which mean increased flooding risks
- River straightening- increases velocity/turbidity (more sediment)
What is the hydrological concept of stationarity, and why is it no longer considered a valid assumption in water resources management?
- Stationarity- the idea that natural systems fluctuate within an unchanging area of variability
- Made obsolete by human involvement in land cover change, climate change, river redirection/dams.
What are the hydrologic implications of stationarity being “dead”, and how does this condition impact our understanding of watershed behavior and water resources management?
- Illustrates that it no longer applies and cannot be assumed in hydrologic estimates
- Must find new analytic strategies that incorporate this change into hydrologic usage.
Manny’s equation
- applies to uniform flow in open channels and is a function of the channel velocity, flow area and channel slope
- assumes uniform flow conditions, bottom slope is the same as the slope of the energy grade line/water surface slope
- n is a coefficient which represents the roughness or friction applied to the flow by the channel
