Concepts

Question 1

Catchment Water Balance

Answer 1

Inputs: precipitation P + groundwater inflow IGW
Outputs: evapotranspiration E + groundwater outflow OGW + streamflow Q

Question 2

When to use velocity-area?

Answer 2

• calmer, predictable flows, weak mixing

- can be made by wading, cable spanning the channel, hydro-acoustic

Question 3

When to use dilution gaging?

Answer 3

• highly turbulent, cross-sectional area difficult to measure, hazardous conditions, mobile bed, rapid mixing
• tracer must be conservation, found naturally in low concentrations, and not pose a significant risk to aquatic life

Question 4

Constant rate injection

Answer 4

best suited to smaller streams/lower flows (<1 m3/s)

Question 5

Slug injection

Answer 5

“relative concentration method” (pre-mixed)
limited to discharges up to about 10 m3/s due to logistical challenge of mixing and handling larges volumes of salt solution

Question 6

Slug injection of dry salt

Answer 6

“mass balance method”
has been used to measure discharges of 100s of m3/s
best if salt is at least partially dissolved in brine to avoid dry salt setting on bed of stream

Question 7

Rating Curve

Answer 7

concurrent measurements of stage and discharge plotted
rating curves are not always stable
monitoring sites should be stable, low turbulence, easy to read

Question 8

Hydraulic Structures

Answer 8

Geometrically defined controls constricting flow to generate a consistent stage-discharge relation

• Weirs: designed to minimize approach velocity, trap sediment
• Flumes: velocity approach, allows sediment to flush through, self-cleaning

Question 9

Gauge under catch causes

Answer 9

Mainly wind, also:

• wetting: initial rain held on funnel surface by adhesion and to recorded
• measurement height: lower height = decrease wind speed, but increased possibility of splash-in from ground
• changes in vegetation or land use near gauge can introduce spurious change sin measured precipitation

Question 10

Orographic processes

Answer 10

Upward deflection: air forced over topographic barriers
Orographic augmentation of other lifting mechanisms
Fictional effects: increased duration of storms
Topographic convergence
Seeder-feeder mechanism

Question 11

Characteristics of convective precipitation

Answer 11

Summer, esp. in afternoons on sunny days.
Scattered cell each 1-10 km in scale
Minutes to an hour
High intensity

Question 12

Characteristics of frontal precipitation

Answer 12

Dominantly autumn and winter
Spatially expensive (10s-100s of km), warm fronts more extensive than cold fronts
Hours to days, warm fronts longer than cold fronts 
Low to moderate intensity (warm fronts), cold fronts be can more intense

Question 13

Elevation and Continentality

Answer 13

Variations with elevation
Rain shadow effect
Interactions between topography and weather systems
Lake effect
Seasonal variation

Question 14

Extreme value assumptions

Answer 14

1. events are independent
2. the precipitation events are generated by the same meteorological mechanism
3. the event probabilities do not vary through time

Question 15

Interpretation of extreme value graphs

Answer 15

1. if all assumptions are valid, data points should fall roughly along a straight line
2. it is not uncommon to have one or two outliers at the upper end due to sampling
3. “dog-legs” indicate possibility that more than one type of event is represented: one responsible for lower intensity values and another for higher intensities

Question 16

Functions of interception

Answer 16

Reduces amount of water reaching the ground
Modifies spatial pattern of water reaching the ground
Can reduce kinetic energy of water reaching the ground
Modifies chemistry of water reaching the ground

Question 17

Controls on interception

Answer 17

Canopy characteristics: species (shape and orientation of foliage and branches), canopy density or leaf area index
Weather/climate: storm intensity (shaking), storm duration (does the canopy become saturated), wind speed (shaking), air temperature, humidity, solar radiation

Question 18

Empirical vs process based-models

Answer 18

Empirical: require less input data, need to be calibrated to data, and may not be transferable to other situations. Based on a linear relation between IL and P

Process-based: in principle require little or no calibration and are transferable in time and space, typically require extensive input data that are frequently unavailable especially in operational situations

Question 19

Tensiometer

Answer 19

Moisture content in an unsaturated soil is related to water pressure (“soil moisture retention curve”)
Measures water pressure and provides an indirect measure of soil moisture changes
Complicated by “hysteresis” in the relation between soil water potential and water content

Question 20

Well

Answer 20

Water level inside indicates depth of the water table

Question 21

Piezometer

Answer 21

Water inside has the same hydraulic head as water in soils surrounding the screen at equilibrium

Question 22

Hysteresis

Answer 22

Differences in contact angle between wetting and drying phases
Entrapped air bubbles on wetting phase
Ink bottle effect

Question 23

Causes of anisotropy

Answer 23

Orientation of clay minerals in sedimentary deposits and soils, layering (e.g. fluvial deposits)

Question 24

Factors causing the decline of hydraulic conductivity with decreasing water content

Answer 24

Volume of soil that is conducting water decreases
Velocity of flow decrease as water films get thinner (increased friction)
“Tortuosity” of flow paths increases (longer flow path = longer travel time)

Question 25

Green and Ampt

Answer 25

• assume uniform soil properties and initial water content, no confining layers, water table far below surface
• invoking the water balance for the assumed condition, the infiltration rate
• early in event, hydraulic gradient is dominated by pressure head gradient, leading to high infiltration rate
• later in event, pressure head gradient declines, and hydraulic gradient becomes dominated by gravity

Question 26

Hyporheic exchange

Answer 26

• involves the infiltration of stream water into the bed or banks, after which it flows some distance downstream before discharging back into the stream
• depends on morphology of stream and riparian zone

Question 27

Evaporation pans

Answer 27

E = P - h
h = change in water level
heat exchange across sides and bottoms
small water bodies tend to have higher evaporation than larger water bodies due to their reduce "fetch" 
heat storage changes seasonal timing

Question 28

Potential Evapotranspiration Models

Answer 28

Thornthwaite’s: empirical, based on measurements of E from well-watered pyrometer, requires only air temperature and day length
Hergreave’s: empirical, calibrated using well watered lysimeters
Penman’s: combines energy balance with aerodynamic formulae for Qh and Qe
Priestly-Taylor:

Question 29

Models of actual evapotranspiration

Answer 29

Penman-Monteith: assumes canopy can be treated as a big leaf
Soil-moisture balance: assumes plants act like passive wicks, coming approach in operational hydrological models
Modified Priestley-Taylor: uses empirically defined coefficient 𝛼’ which varies with soil moisture (due to the effect of soil moisture on hydraulic conductivity and ability of water to move in soil)

Question 30

Snow storage controls

Answer 30

Elevation, wind, vegetation, avalanches, interactions

Question 31

Snow albedo depends on

Answer 31

snow grain size and shape, dry versus wet, fractions of direct and diffuse radiation, incidence angle for direct radiation

Question 32

Lysimeters (snow)

Answer 32

Measures vertical water drainage

Drain hole with stone placed to minimize clogging by leaves and needles

Question 33

Time of concentration

Answer 33

The time taken for a molecule of water to travel from the most remote part of a catchment to the catchment outlet

Question 34

Infiltration-excess

Answer 34

“Hortonian overland flow”
Occurs when rainfall intensity exceeds infiltration capacity of soil
“fill and spill” in depressions– controls connectivity between upslope areas and stream channel
stormflow is “direct runoff”

Question 35

Saturation-excess

Answer 35

Rising water table

Total “saturated-excess overland flow” = direct precipitation on saturated source areas + return flow

Question 36

Source area concept

Answer 36

Areas contributing water to streamflow vary intimate and space, primarily controlled by soil moisture conditions

Question 37

Partial-Duration curves

Answer 37

Analyze all peak flows above some threshold

Statistical theory less well developed

Question 38

Annual extreme flood series

Answer 38

Analyze only the highest flow each year

Statistical theory well developed

Question 39

Bank storage

Answer 39

Channel water infiltrates banks on rising limb, reducing streamflow in channel; water discharges back into the channel on the falling limb

Question 40

Role of forests

Answer 40

Transpiration, increased interception with age, high infiltration capacity