Surface Water 2

fill and spill hydrology

where there are many depressions in a watershed, a rainfall will replenish groundwater - needs enough volume to spill over in order before connecting to downstream parts of catchment

in prairies, bedrock, etc - praire potholes

how does changes in a wetland impact hydrological regime

draining wetlands alongside other changes will alter the natural drainage area to be larger and encompass a larger area etc

storage decreases which increases runoff

flooding

can be fluvial (overflows over banks), pluvial (rain), coastal (storm surge, tsunami)

knowing risks is very important with land use etc of floodplains

• flood frequency, changing risk, erc

flood frequency

understanding frequency and magnitude based on historical methods

return period - how often can we expect a flood greater than a specific discharge

exceedance probability of the large flood in a given year

important to understand how parts of a flood plain will be flooded - city planning, insurance, etc

return period equation

= (n+1)/Rank
(n - years of record)

probability equation

Rank/ (n+1)

probability of a flood of a certain amount occuring

levees

constructed to prevent/protect against flooding

BUT can increase further downstream and runoff is faster

and also can be catastrophic when it fails

calgary flood control

2013 flood was extremely costly

additional control needed in bow and elbow rivers, springbank reservoir added storage

glenmore reservoir also added storage

dam under assessment, additional levees built, dry dam created

non-stationary flood frequency

future =/ the past

need to account for climate change, land use/management (ag, forestry, etc), fires, dams/diversions/drainage, and alteration of river channel

need to account for these in modelling and projections

river morphology

headwaters (in the mountains), transfer zone comes next where lower elevation streams merge in lower slopes

in the depositional zones meandering streams flows maybe into delta, maybe sea, etc

stream power

rate of energy dissipation against the bed and banks of a river per unit downstream in length

work done by a stream to move sediment

so for example a river flowing at a constant speed which does not gain any kinetic energy needs to dissipate energy in some way and so it does as kinetic energy for sediment, ______

stream power equation (Ω)

Ω = p*g*Q*S

p = density of water, g = acceleration due to gravity, Q=discharge, S = slope

stream power interpretation

steep rivers with a higher discharge will have greater stream power therefore a higher power to transport/erode sediments

with no sediment stream power is instead dissipated as heat vs kinetic energy

river zones and sedimentation

in the headwaters usually supply of sediment is higher than the rate of deposition, therefore stream power acts on the supply

in the transfer zone floodplain pockets begin to form, supply/sedimentation and deposition are more equal

in the depositional zone the supply is less than, therefore floodplains are continuous and deposition is constant

total suspended solids

measured by filtration and weighing of the filter before and after

filter pore size determines difference between a dissolved and suspended solids

dominated by silt, clay, sand but can also include organic material

increases with higher stream velocity

bedload

sediment particles which are too heavy to be suspended

move by rolling, sliding, and saltation

needs stream depth 10x sediment diameter

increases with higher stream velocity

entrainment and deposition

higher velocity needed to entrain (erode) than to keep sediment in suspension

smaller particles easier to keep in suspension, easier to erode (exception of clay/silt)

deposition caused by lower stream velocities, TSS and bedload increased with higher V

larger rivers able to transport more TSS and bedload

yield

total amount of sediment or other dissolved transported in a river over time, largely during high flow as Q increases with C

ex tonnes/year

= D*C (discharge * concentration)

dendritic

trellis

rockies

radial

centripetal

rectangular

cracking landscape

deranged

prairies, depressions

parallel

braided river

higher bedload, more grained sediment, decreasing bank stability, high discharge variability, high slope

channel type in the transfer zone

meandering pattern

more suspended load, finer grain sediments, increasing bank stability, low variability discharge, low channel slope

sinuosity >1.5

channel type in the transfer zone

sinuosity

length of thalweg / distance along valley

meandering river will have >1.5

alluvial fans

base of mountain

deposition when river slows down - less slope and loss of stream power

deltas

in lakes or oceans, lots of sediments - silts and clays

deposition when river slows down - less slope and loss of stream power

sediment trapping in dams can reduce sediment load here, when wave erosion>deposition then they will shrink

human modifications of sediment transport

urbanization increases runoff, increases erosion and river incision ex in the mill creek ravine

reservoirs trap sediments, and when there is less in water downstream then increases erosion and stream incision

this can also reduce sediments in deltas which causes them to shrink (when wave erosion>deposition)