Stream Flow Flashcards
Why is stream flow important?
-high flows are important to estimate flood discharge
-low flows important to understand water requirements, min flow to support navigation, recreation, and aquatic life
Flow is represented by change in discharge with time
Factors affecting hydrographs
-Precipitation characteristics,
rainfall intensity and pattern
type, size and direction of storm movement
-watershed characteristics
Size and shape of drainage area
Soil type and land use
Storage in watershed
Direct runoff - rapid response
-generated by precipitation
-all overland flow and precipitation directly on stream
-main contributor to peak discharge
Indirect runoff - slow response
-subsurface runoff generated by precipitation
-interflow
-base flow
Interflow -moderate response
-slower than direct runoff
-infiltrated water that moves laterally in subsurface until reaching channel
-consists of quick interflow which contributes to direct runoff
-delayed interflow which contributes to base flow
Base flow - slow response
-groundwater runoff and delayed groundwater runoff contributes to channel
-extremely slow
Channel precipitation
-originates from rainfall on the stream and water bodies connected
-average precipitation multiplied by area covered by water surface
Major components of stream flow
-base flow
-direct runoff
Minor components of stream flow
-interflow
-channel precipitation
Streamflow measurement
-direct method
Discharge measure with velocity area method. Taking multiple measurements across stream and mtiltpliying them by the area of the cross section
-indirect method
Establishes a rating curve based on the relationship between the water storage and the discharge
Rising limb
-represents increase in discharge due to the gradual building up of storage in channels
-the climate factors generally control the rising limb
Crest of hydrograph
-where the peak flow occurs due to the runoff from various parts of the watershed contributing to the max amount of flow at the outlet
Recession limb of hydrograph
-extends from the point of inflection at the end of the crest to the start of natural groundwater flow
-represents withdrawal of water from the storage built up in the basin
-starting condition represents the condition of max storage
-determined by catchment characteristics
Hydrograph in a humid climate has what characteristics?
-continuous
-not smooth
-high infiltration
-spikes caused by rainstorm
Hydrograph in a arid climate has what characteristics?
-not continuous
-not smooth
-mostly direct runoff
-long period where channel is dry
-little infiltration
Snowfed river hydrograph has what characteristics?
-continuous
-relatively smooth due to steady release from the snowpack
-most of base flow is due to snowmelt
Hydrograph analysis serves what purpose?
-examine a storm hydrograph and determine the relative contribution of direct runoff and base flow
Why do we separate base flow (hydrograph separation)?
-to quantify the contribution of precipitation and ground water to stream flow
-to identify water quality associated with surface water and subsurface water
Hydrograph separation methods?
-straight line
-fixed base
-variable slope
