Surface Water

strahler stream order and names

1st order means headwaters (2nd order when two first meet, 3 when two seconds, etc)

usually history/tradition determines the name, or the greater volume/depth

how does water fill a stream?

runoff generation → overland flow, interflow, groundwater flow, return flow

pathways such as transit time, water chemistry and erosion

depression storage (fill/spill)

overland flow

infiltration excess or saturation excess

will reach rivers and streams very quick, low interaction with soil, low solutes

more likely in urban areas, less likely in forests which has higher infilitration, fires and also increase

infiltration capacity

mm/hour

determined by soil properties, rate of i

ex sandy soil > loamy > frozen

occurs if rate of precipitation > than the infiltration capacity (hortonian overflow)

throughflow/interflow

water in a homogenous unsaturated zone should only move by gravity or downwards

but if there are distinct differences in pore size or permeability water may be more likely to move laterally than downwards

above the regional groundwater table

in unsaturated zones water is held in pores by capillary forces

this capacity increases with smaller pore sizes (clay>sand)

groundwater flow

a continuum of water with different transit times to streams

some respond to rainstorms, others only respond to climatic changes over years

sustains rivers even during droughts

gaining rivers

receive groundwater discharge from watershed, adds to streamflow

losing rivers

recharge groundwater, since the table is below the river

common when rivers leave wet regions and pass through dry

streamflow equation (Q)

= discharge (m3/s, or volume over time)

= velocity * area

velocity is not constant, friction of channel/bank/air slow down the flow

total stream discharge is the sum all subsections

how to measure streamflow

measure at 60% depth (the average) for many subsections (maybe 10) to get a good estimate

the highest would be at the top and the lowest at the bottom

measured with propellor, sensors in large rivers, flow meter in small creeks, weirs, salt dilution, etc

v-notch weirs

discharge known from stage (water level) behind compared to discharge at the level of notch

compute how much is actually going over, Q

another measure of streamflow

salt dilution

pour in tracer solution with high salt concentration, then measure electrical conductivity at a distance downstream

using EC, time and distance can calc streamflow, Q

does impact the environment, but can also use dyes

continuous discharge data

recorders can get high frequency data for water level/high/low flow

verified by staff gauges - measured every hour

the rating curve is used to get discharge from this data, specific for each water way

rating curve

the relationship between discharge and water level (unique to each site)

allows use to translate the water level into the discharge

runoff

the amount of water that moves into streams and further downstream, divided by watershed area

= volume/area * 1000 (bc in mm)

in mm

the depth of water for an area that becomes river discharge

water balance

change S = P - ET - R ± GW

change in storage = precipitation - evapotranspiration - runoff ± groundwater (inflow or outflow)

in mm

if change in S and Gw are zero, R= P-ET

runoff ratio

= R/P

the ratio between runoff and precipitation, hydrological efficiency

indicates how much precipitation becomes runoff

units must match**

so for ex high in west coast, very low in prairies

variability in runoff ratio

topography, steepness = higher ratio

clay soils have higher ratio (low infiltration)

drainage channels increase

lakes provide storage, decreases

vegetation increases

wetlands are variable

urban infiltration

increases runoff, decreases evaporation, decreases infilitration

need mitigation practices such as wetlands, rainwater harvesting, green areas, etc

hydrograph

follows discharge over time - can be 1 storm or 1 year

lag time, flood magnitude, recession timing and R/P all vary on - size, steepness, infiltration, groundwater pathways, wetlands/lakes

other factors like wet/dry soils, frozen soils, and storm magnitude

baseflow

before rain, supported during dry periods by groundwater or interflow paths

rising limb

hydrograph during rain

peak discharge

highest/flooding level on a hydrograph

lag time

the difference between peak rainfall and peak discharge on a hydrograph

falling limb

recession on a hydrograph

storm runoff

quick flow

old water paradox

stream flow separated into quickflow (considering overland) and baseflow (considered ground) on a hydrograph

headwater streams have rapid response in flow to rain (new water), yet after a rain the stream water still has characteristics of the old water…

how is it that new rain pushes out old water? esp when old water is considered the GW

water capacity holds water

old water paradox displacement flow

/piston flow

discharge is often not the overland flow we think it is

new water is pushing old water into stream

hydrograph comparisons

characteristics depend on watershed size, steepness, infiltration rate, wetlands/lakes, soils, climate, storm magnitude, etc

so for example a large watershed has longer lag time but higher peak flow, more steep means higher peak flow, plains have higher peak and lower lag as compared to forests, and impermeable soils will have lower lag and higher peak

hydrological regime components

magnitude - timing and peak of baseflow, annual runoff, R/P

variability - frequency/duration of exceedance, flashiness (spikey), predictability

nival regime

streamflow dominated by snowmelt, followed by generally receding flow during summer

glacial regime

streamflow dominated by glacial meltwater, peaks during summer months

pluvial regime

streamflow dominated by rain events during a wet season - winter months in coastal canada

mixed regime

streamflow with characteristics of more than one

anthropogenic regime

dams, urban, forest harvesting, irrigation

hydrological regime exceedance prob

on a flow duration curve, shows percent of time where discharge is at a specific level