Topic 5: Surface Water Flashcards
what does surface water include?
streams lakes glaciers snow soil water vegetation wetlands
what percentage of Canada does freshwater make up?
8.9% or 891,163km^2
gravity force in water flow
moves water down rivers and drives a conversion from potential energy to kinetic energy
where is flow highest in a stream cross section (bank, or middle)
middle
name the 4 types of water flow
laminar
turbulent
steady
unsteady
which three things does Froude number use?
v= flow velocity vw= surface wave velocity H= water depth (height)
name and explain the three types of Froude flow
- subcritical turbulent flow where velocity is less than wave velocity Fr<1
- Critical flow where flow velocity equals wave velocity Fr=1
- Supercritical laminar flow where flow velocity s greater than wave velocity and Fr>1
what causes river velocity to change?
stage and discharge
define stage and discharge
stage= water level
discharge is a function of stage
how do you measure stage
using the building with the float and counterweight
how can you measure discharge
velocity area method
Q=A x V or (W x D)xV
T or F: discharge increases with an increase in depth, width or velocity?
true
quickflow vs baseflow
base flow doesn’t respond from large rain events, sources from groundwater vs quick flow responds to precip. events and rapidly delivers water to streams.
perennial vs ephemeral streams
Perennial stream has continuous flow in stream bed all year round (Cowichan river)
Ephemeral: channels that flow for hours or days following rainfall or snow melt (3rd, 4th 5th order streams).
hydrograph characteristics depend on what
precipitation (magnitude, intensity, duration, distribution) basin characteristics (slope angle, soil type, soil thickness, initial moisture conditions, basin size and shape)
what is a unit hydrograph used for
to predict discharge/floods
describe overland flow and what influences it
non-channeled water flow over the ground surface.
- precip intensity
- snow melt rate
- pre-existing soil saturation level
- ground cover
- soil type
- topography
name the two types of surface runoff from rain or snow melt
infiltration excess overland flow
saturation excess overland flow
describe infiltration excess overland flow
occurs with soil that is not saturated, soil properties or land cover do not allow for infiltration to keep up with high rainfall or snowmelt rates. (Hortonian Flow)
explain saturation excess overland flow
occurs when the soil becomes saturated and no longer space for water to infiltrate
define flooding
rising stage level associated with excess discharge in response to storms of seasonal melt. it is a natural process required to maintain river form and function. defied by channel cross-section and bank height
what does bankfull mean
threshold stage before river flows over banks
how to predict floods
- hydrograph
- recurrence interval (R) which is the annual peak discharge records used to predict flood probability (P)
- rational method which estimates peak annual discharge using empirical formulae and data on rainfall ad basin stats
facts about flooding in N. America
- rates of urban growth in floodplains is 2x of other areas
- BC experiences the largest floods in N. America from high intensity precip with rapid mountain runoff.
