5: Surface Runoff Flashcards
What is runoff?
Surface water flow formed by precipitation that doesn’t infiltrate
What is depression storage?
Water that is held in puddles or small depressions
What is interflow?
The lateral movement of water through shallow surface soils, a.k.a. subsurface lateral flow or throughflow
What is interception loss?
Precipitation stored & evaporated due to interaction with vegetation i.e. precipitation that does not contact ground or water surface
What is interception store?
Precipitation retained by vegetation, does not contribute to runoff
What is throughfall?
Rain that passes through a vegetation canopy, including water that drips from leaves
What is stemflow/trunkflow?
Water that originates from precipitation, that travels down tree trunks or plant stems
What is Hortonian runoff?
Soil has saturated from rainfall and excess rain moves downslope to the stream as runoff, saturates from ABOVE
What is saturated overland flow?
Light precipitation doesn’t saturate soil but causes water table to rise, soil saturates from BELOW
What is the water table?
The elevation where groundwater is at atmospheric pressure
What is a piezometer?
Vertical pipe placed into ground to measure elevation of water table
What is transmission loss?
Loss of water from streamflow when water infiltrates into stream bed or floodplain
Describe the shape of a flood wave.
A flood wave is not symmetric; the advancing front is normally steeper than that receding tail
What is a rating curve?
Stage vs. discharge
Relationship between river level (stage) and discharge, can change over time depending if flood wave is advancing or receding (results in ‘looped’ rating curve)
How is a rating curve determined?
Direct measurement (stage vs. discharge) or theoretically if hydraulic control is available (e.g. weir)
Where is ‘average’ velocity occur in a cross section? When is this approximation valid?
Average velocity is taken at 60% depth from the water surface,
Valid for uniform flow in a wide channel
What are some flow measurement methods for stage and discharge?
Stage:
- visual, float, pressure sensor, electrical resistance
Discharge:
- flowmeters, weirs/flumes/orifice, floats, dilution
How do you estimate the discharge of a wide section using sub-area velocities?
Q = ∑AiVi
What is quick flow?
Rapid component of catchment runoff in response to rainfall
What is base flow?
Slow component of catchment runoff in response to rainfall, usually result of groundwater discharge to a stream
What is recession?
Decline in streamflow that occurs after a flow peak
What is a hydrograph?
Graph of flow vs. time
What is a hyetograph?
Graph of rainfall per time period vs. time
What is the relationship between a hyetograph and a hydrograph?
A hyetograph shows the rainfall per time and the hydrograph shows the resulting flow in response to this rainfall. The peak of the hydrograph occurs after the rainfall peak (lag)
What are the St Venant equations used for? What are the assumptions?
Kinematic wave approximation Assumes: - pressure & inertial forces not important - gravity & friction forces balance - water surface is parallel to bed
In a rating curve (stage vs. discharge) what does the ‘stage’ represent?
Water level (elevation of water surface)
