Quiz 8+9 Flashcards
(27 cards)
Stream flow responde determined by
-spatial and temporal variability in rain
-travel time from watershed area to stream
-travel time from channel entrance to outlet
-slope
-watershed shape
-drainage patterns
-soils and geology
Measurement of stage
-height of water surface above arbitrary datum
-manual: staff gauge
-automated: sitting well float
Measurement velocity
-distance traveled per unit time
-standard is a six tenths depth
Measurement discharge
-rate at which water passes through a given cross section
-destermined using velocity area method
Measurement rating curve
-relationship between stage and discharge to each stream.
-uses non linear regression
Rational method
-used to predict peak flow rates in small watersheds
Runoff generation
-factors affecting
1.precipitation form and intensity
2.storage/soil moisture
3.spatial distribution
4.covergence of flow pathways
5.land use or land disturbance
VSA (variable source area)
-most of the storm flow by interflow and saturation Overland flow to stream channel
-infiltration not a limiting factor
-watershed area not a direct index of flow response
-assumes only part of a watershed is making direct contribution to storm flow
Primary contributors
1.interflow
2.saturation excess Overland flow
Vsa vs partial
Spatial
1.partial-fixed in area space
2.VSA-expand and contract overtime
Source if water
1.)partial
-INFILTRATION excess Overland flow
2.)VSA
-interflow and saturation excess
Erosion
-detachment and transport of unconsolidated material from one place to another
Erosion impacts
-nutrient loss
-reduce infiltration
-fills resevoirs
-affects aquatic organisms
-drinking water quality
-carries toxins
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Erosion phases
-detachment
Rain drops falling on ground and flowing to dislodge material E=(M)(Vt^2)/2
-transportation
Detached particles moved down hill
-depostion
Particles eventually accumulate somewhere (sedementation)
Sheet erosion
-relatively uniform erosion over entire soil surface
-requires Overland flow and is often exacerbated by raindrop impact
Rill erosion
-most common form of soil erosion
-occurs when Overland flow breaks up into small channels or microrills
Gully erosion
-when depth of a rill is greater than .3m
Surface erosion in forest
-high infiltration and interception makes erosion generally not an issue in forest
Mass movement commonality
-most common in OR, WA, AND CA in coastal and mountain areas
Mass movement factors
-vegetation, topography, land use, precipitation.
Arid, sparse veg = mudflows/debris
Humid/dense veg = earthflows/soil creep
Mass movements slide hazar
-slope > 80% except 75% in tyce core area
-headwall configuration
-geology: coast range sandstone with sequences of turbiditbeds
Mass movement slides
-down slope movement of soil or rock on a surface of rupture
-occur in response to extreme rain events, snowmelt, grading, adding loads to top slope
Two types
1.translational:movement along a roughly planar surface
2.rotational: curved concavely upward
Forces promoting failure
F = resistance of soil to failure / forces promoting failure
Safety factor
- _< 1 imminent failure
->_1 increasing slope stability
Debris flow
-form of rapid mass movement in which loose materials flow downslope
-source area: steep gullies
Soil creep
-very slow (mm/yr)
-caused by sheer force not great enough to cause failure
-evidence is curved trees
Erosion measurements
-silt fences
-erosion pins
-rainfall simulator
