river discharge

Question 1

Runoff equation

Answer 1

Runoff (L/T) = discharge (L^3/T) / catchment area (L^2)

Question 2

Streamflow definition

Answer 2

volume of water flowing through stream channel

Question 3

Stream discharge definition

Answer 3

volume of water that flows past a given point in a stream in a unit of time

Question 4

Stream discharge equation

Answer 4

Discharge = width x depth x velocity
-reported in cubic feet per second (cfs) or m^3/sec or L/sec

Question 5

single-instance flow estimation methods

Answer 5

-floating object and measurement of travel time (apply correction factor)
-manual measurment of width & depth AND dilution gauging for velocity
-velocimeters

Question 6

continuous flow estimation

Answer 6

-continuous water depth & velocity measurements (costly & logistically difficult)
-continuous water depth AND rating curves

Question 7

Dilution gauging

Answer 7

instantaneous water velocity for a given location obtained by dumping dye in upstream water and calculating the time before dye in the stream reaches someone downstream
-useful for small and rough stream

Question 8

velocity area equation

Answer 8

discharge = average flow velocity x transversal section area

Question 9

velocimeters method

Answer 9

give instantaneous water velocity for given river location
-should be measured at 60% of full river depth (where average velocity occurs)

Question 10

Acoustic Doppler Current Profilers (ADCP)

Answer 10

measure instantaneous/continuous water velocity AND depth
-using soundwave to measure 3D velocity of whole water column

Question 11

Pressure transducers & velocimeters

Answer 11

measures continuous water depth & velocity
-can be directly in river OR in gauge house connected to river by pipe

Question 12

Pressure transducers definition

Answer 12

measures water pressure exerted on top of instrument and use calculations to transform in into water depth

Question 13

weirs & flumes

Answer 13

artificial controls to force flow through critic depth at which Q is known
-flume: concentrate flow at one particular location
-weirs: using V-shape to concentrate flow at bottom of V

Question 14

rating curves usage

Answer 14

used to convert water depth into discharge based on statistical relationships

Question 15

rating curves considerations

Answer 15

errors occur when measuring flow velocity
diff rating curves for diff seasons
changes shape when river floods

Question 16

Steps to build rating curves

Answer 16

1. measure water velocity at diff water lvl
2. use stream flow equation to calculate discharge
3. build relationship between water lvl and discharge value
4. use rating curve to predict discharge from any water lvl value

Question 17

hydrograph definition

Answer 17

graphical representation of stream discharge VS time
-how watershed as a whole responds to precipitation event
-can be for single event, season, year, etc.

Question 18

2 types of hydrograph assessment

Answer 18

-hydrograph separation
-hydrograph analysis

Question 19

hydrograph separation components

Answer 19

breaking hydrograph to distinguish generic flow components
-stormflow: portion fed by rapidly moving runoff in response to rainfall or snowmelt (subsurface & overland flow)
-baseflow: portion fed by slowly moving runoff even in absence of rainfall or snowmelt (GW)

Question 20

hydrograph separation methods

Answer 20

-Linsley’s fixed interval method
-recession limb method
-isotope-based hydrograph separation
-chem hydrograph separation
-straight line method

Question 21

Linsley’s fixed interval characterstics and formula

Answer 21

formula: A^0.2
-only need watershed area
-create multi-segment line

Question 22

straight line characteristics and formula

Answer 22

formula: 0.05 pi^3 x h^-1 x A
-only for watershed smaller than 20 square miles
-slope proportional to watershed area
-most frequently used

Question 23

rising limb definition

Answer 23

period when stream discharge increase in response to rainfall or snowmelt event

Question 24

falling limb definition

Answer 24

period when stream discharge decreases after rainfall or snowmelt event

Question 25

rising limb shape and runoff types

Answer 25

steep: quickly generates & fast-moving runoff (overland flow)
less steep: slower moving runoff (subsurface flow)

Question 26

Lag time 2 definitions:

Answer 26

1: time interval between center of mass of precipitation and center of mass of event stream hydrograph
2. Time interval between peak precipitation and peak of event stream hydrograph
-short = overland flow/ slow = subsurface flow

Question 27

time to peak

Answer 27

time from beginning of rising limb to occurrence of peak discharge
-good indication of dominant runoff (short = more surface runoff)

Question 28

Time to concentration

Answer 28

time from end of precipitation to inflection point of recession limb of event hydrograph
-how much time until last raindrop feed stream via runoff

Question 29

time base

Answer 29

duration of the event stream hydrograph during which quick flow occurred

Question 30

elongated VS circular watershed timing

Answer 30

circular: shorter distance in watershed = short time of concentration / higher peakflow/ shorter lagtime/ shorter peak duration
elongated: longer time of concentration/lower peak value/ longer lag time/ longer peak duration

Question 31

Runoff ratio definition and formula

Answer 31

Amount of precipitation that was made into runoff and made it to the outlet -> computed by dividing the volume of stormflow by the volume of water input
2 formulas option:
- Rp = total stormflow/total precipitation
-Ry = total stormflow/ effective precipitation

Question 32

9 Most IMP factors affecting runoff and storm hydrographs

Answer 32

-watershed area
-stream order
-shape of watershed
-regional climate/ type of precipitation/ antecedent moisture conditions
-topography
-geology and soil
-land use and land cover
-drainage condition -> (natural drainage density, tile drains, etc.)
-depression storage feature -> (wetlands, man-made reservoirs, etc.)

Question 33

arid VS humid climate hydrograph

Answer 33

arid:
-soil characteristics & hydrophobicity -> HOF = shorter lagtime
-larger volume of water with overland flow = higher peak
-quick flows because overland = small peak duration
Humid:
-mostly subsurface flow = longer lag time
-lower & flatter peak -> water doesn’t reach stream all at same time

Question 34

climate as natural watershed factor

Answer 34

-precipitation
-antecedent conditions
-time of year/season
-other conditions affecting evapotranspiration

Question 35

characteristics of watershed as natural factor

Answer 35

-watershed area
-shape of watershed
-elevation
-slope
-lenght & slope of valley

Question 36

river network as natural factor

Answer 36

-routing and detention
-drainage density
-river conditions
-size of river (stream order)

Question 37

surface depression as natural factor

Answer 37

-storage, hydrologic balance

Question 38

reservoir as natural factor

Answer 38

-store IMP volume
-prevent/delay runoff
-water extracted reduced stream discharge
-dry reservoir = temporary storage during flood

Question 39

geological & soil characteristics as natural factors

Answer 39

-bedrock permeability
-soil permeability
-thickness of soil
-infiltration capacity
-initial conditions

Question 40

Land use as anthropogenic watershed factors

Answer 40

-irrigation & drainage ditches
-tillage on wetlands and subsoil compression
-urbanization
-direct influence on retention capacity & many water budget components

Question 41

measures to mitigate high streamflow

Answer 41

-increase afforestation
-increase meadow area at expense of arable land
-limit construction of impervious surface
-promote implementation of infiltration areas & permeable pavements

Question 42

flood frequency use

Answer 42

long term analysis of daily/ weekly flows allowing determination of important seasonal differences

Question 43

perennial stream definition

Answer 43

water flowing year-round with water table above the streambed for most of the year -> GW is primary source of water and direct precipitation and runoff are supplemental ones

Question 44

intermittent stream

Answer 44

water is flowing during certain time of the year only when GW provides water to the stream (when the water table is high enough)
-may not have flowing water during dry period

Question 45

ephemeral stream

Answer 45

water flowing only for short period of time after rain events as event runoff triggers streamflow (streambed above water table = no GW as source)

Question 46

flow duration curve definition

Answer 46

cumulative frequency curve showing the percentage of time that a specified discharges value are equaled or exceeded
-highest flow -> lowest % of exceedance

Question 47

flood definition

Answer 47

occurs anytime a waterbody overtops natural/ artificial banks in any reach of a stream -> water above bankful level

Question 48

high water definition

Answer 48

highest water level reached during a flood

Question 49

flood implication for envr and society

Answer 49

-high risk & damages to human with extreme floods
-regular natural events that trigger ecological processes and shape river channel
-floodplain are important ecological system that help attenuate flood waves and are used for agriculture

Question 50

what is a 100-year flood

Answer 50

it is a flood of given size that has a probability of 1 over 100 chance of occurring every year based on historical data

Question 51

structural flood control measures

Answer 51

measures linked to engineering efforts
-embankments
-channelization
-diversion
-storage structures (dams & reservoirs)

Question 52

non-structural flood control measures

Answer 52

measures linked to sound floodplain management
-identification of high-risks areas
-zoning regulations for development