Runoff Spring 13 Part 1

8/10/2019 Runoff Spring 13 Part 1

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GEOG370 Hydrology Spring 2013 D.L. Peters

9.1 Runoff Processes

flow of water over land in thin layers & channels includesmany direct & indirect components:

river discharge, Q [L3 T-1] in channel as m3s-1

channel precipitation, Qp often small river area 1-2% of basin

overland flow, Qo (aka excess ppt, Pe)

sheetflow, rills, gullies ppt impact & erosion

throughflow, Qt lateral downslope flow above water table

groundwater flow, Qg

emergent baseflow in rivers & springs


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Hortons (1933) overland flow

first conceptual model to partition stream flow Q into runoff

(Qo) & groundwater (Qg) components

land surface partitions water into infiltration vs. surface runoff

components

when rainfall intensity (i) > infiltration capacity (f), excess ppt (Pe) will

flow as Qo

infiltration excess overland flow or Hortonian overland flow (HOF)

all other moisture percolates to groundwater table

based on observations in arid basins with low permeability

limitations? rarely occurs in forested basins!


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Hortonian overland flow (HOF)

i = rainfall intensity

f = infiltration rate

t = point in time

Pe= excess P

Qo = runoff

rainstorm onto

semi-arid

landscape


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Partial Area Concept

Building upon the scarcity of observed infiltration excess, the

partial area concept (Betson 1964) was proposed

Horton overland flow from only a small area of the catchment

is required to produce the storm hydrograph


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Subsurface Flow

By 1960s recognized that most of precipitation

infiltrates the soil surface of forested catchments and

the subsurface flow is the major source of stormflow

number terms all basically denoting same process

subsurface stormflow (Hursh 1936; Hewlett & Hibbert 1967) Interflow (Hertzel 1936; Beven 1989)

saturated interflow (Betson et al. 1968)


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Hewletts (1961) saturated overland flow

on land surfaces, most P infiltrates very little Qo

via HOF infiltration & throughflow (Qt) cause soil zone to reach

saturation, water table rises & eventually emerges as

return flow combines with surface ppt inputs as saturated overland

flow, Qo(s)

thus, only saturated areas provide quickflow allothers absorb & infiltrate very little HOF


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Pressure potential in a straight hillslopeduring course of storm

Soil water close to gravity drainage

Surface layer become wetted

Saturated layer start to form

Flow from upper area

Throughflow (Qt) (fig. 6.21)

especially pronounced

on sloped surfaces re-emergence at base as

return flow

Qo(s)


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Hewletts (1961) Saturated OF


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Variable Source Area Concept (Hewlett & Hibbert 1967)

As a result of infiltration and

subsurface flow the water table in thenear-stream areas rises to ground

surface and expanding the saturated

stream channel area


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Contributions of Hewletts model

more suitable for vegetated, humid-temperate basins

saturated overland flow, Qo(s) as major component of runoff up to 85% of total

50-60% total storm discharge (quickflow) in rivers

30-40% of delayed storm discharge (baseflow)

very small portion (


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Groundwater ridging (fig. 7.9)

originally, Hewlett suggested all

flow infiltrates & travels via Qt

Qo

only on lower slopes by

saturated return flow Qo(s)

later modified to include

groundwater ridge on lower

riparian slopes (Slash &Farvolden 1979)

migrates toward channel &

contributes groundwater pulse

to river flow

delayed baseflow


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Subsurface Preferential Flow (Beven & German 1982)

Flow through soil matrix in forested soils may not be entirely

uniform

preferential flow pathways (macropores) that bypass the soil matrixrapidly transmit subsurface flow to stream channel

Water conducted ahead of wetting front & flow turbulent

Darcian matrix flow uniform laminar flow through soil


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Hillslope Runoff Measurement


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Relative importance of pathways and mechanisms involved in

streamflow generation affected by:

Basin characteristics

climate

topography

pedology

geology

Spatial and seasonal characteristics

maximum saturation contribution in northern areas

occurs during spring when stream valley areas

saturated as result of large water input by snowmelt

quantity of runoff produced will also vary depending on

the moisture within basin prior to storm - wet or dry


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9.2 Stream discharge, Q

volume of water moved per unit time (m3 s-1) through cross-

section of a river channel

calculated using the area-velocity method

Q = A v

where A is area m2 and

v is velocity m s-1

generation, timing & amount of Qs depends on how runoff is

partitioned into Qo, Qo(s) Qt, Qg each has different response time


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Streamflow (Q) Hydrograph

Sto rm d i s ch a rge a t R i t he t C reek We i r ( Jan . 28 -Feb . 17 , 1995 )

0

20

40

60

80

100

120

140

160

1/28/95 2/2 /95 2/7 /95 2/12 /95 2 /17 /95

D at e

Discharge(m

gd)


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Streamflow (Q) Hydrograph

A n n u a l D is c h ar g e fo r R i th e t C r eek (1 995)

0

100

200

300

400

500

600

700

1/1 /95 1/31 /95 3 /2 /95 4/1 /95 5 /1 /95 5/31 /95 6/30 /95 7/30 /95 8/29 /95 9/28 /95 10 /28 /95 11/27 /95 12/27 /95

D at e /t i m e

Discharge(m

gd)


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Measurement of Q: Weirs

Discharge rating curve for Judge Creek - triangular profile flat V weir

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0.0 5.0 10.0 15.0 20.0 25.0 30.0

discharge (m3

s-1

)

stage(m)


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Other examples of weirs

Weirs also used to raise water level


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Rating curves: summer vs winter

208

210

212

214

216

218

220

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000

Discharge (m3 s-1)

Waterlevel(masl)

1964

1967

1968

1980

1990

1996

1972

Peace R. @ Peace Pt. Peace R. @ Peace Pt.

Athabasca R. @ Ft MacMurray

Peace R. @ Peace Pt.

What about a large river?


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Measurement of Q: velocity-area method


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Estimate of Q: Slope Area Method

Difficult or impossible to make measurements during flood

events

Possible to estimate discharge by taking measurements of high

water lines, cross sectional area, and channel slope Use this data in an equation such as Mannings to estimate flow

Manning equation

Q = C/n A R 2/3 S 1/2

Q - discharge (m3 s-1)

C - 1.0 for SI units

S - energy (surface water) slope (m m-1) [head loss per unit length of channel]

R - hydraulic radius [area (m2) divide by length wetted perimeter (m)]

A area (m2)

n roughness coefficient (Mannings)


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0.009-0.011Polyvinyl Chloride (PVC) with smooth inner walls d,e

0.018-0.025Corrugated Polyethylene (PE) with corrugated inner walls c

0.009-0.015Corrugated Polyethylene (PE) with smooth inner walls a,b

0.013Unplaned Wood

0.012Planed Wood0.025Masonry

0.025Earth0.016Asphalt

0.029Gravel0.015Brickwork

0.014UnfinishedConcrete

0.014Clay Tile

0.012Finished Concrete0.010Glass

Non-Metals

0.15Trees0.022Corrugated Metal

0.075Heavy Brush0.012Smooth Steel

0.050Light Brush0.013Cast Iron

0.035Pasture, Farmland0.011Brass

FloodplainsMetals

0.035Stony, Cobbles

0.030Weedy0.040Sluggish with Deep

Pools

0.025Gravelly0.035Major Rivers

0.022Clean0.030Clean and Straight

Excavated Earth ChannelsNatural Streams

Manning nMaterialManning nMaterial


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Hydrograph separation

Conventional hydrograph separation methods rely onsome type of straight-line extrapolation drawn under thestorm hydrograph to partition it into stormflow (alsoreferred to as quickflow & direct runoff) and baseflow(delayed flow & groundwater runoff) components

Q = QB + QS

where Q is the monitored total discharge, QB and QS are the inferredbaseflow and stormflow components of discharge; all have units ofvolume per time


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Baseflow - streamflow generated from relatively slow,long-term drainage of groundwater and delayedsubsurface flow, which sustains streamflow betweenstorms and also provides a continuing flow component

during the storm hydrograph

Stormflow - streamflow generated by a number of rapidrunoff processes (ie. Horton/saturation overland flow and

rapid subsurface flow) which can deliver water to thestream channel in time to contribute to the stormhydrograph


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Line 4

a horizontal line is drawn from the initial rise until it intersects therecession limb of the hydrograph

Use method explained

in lab similar to #3

Documents

Runoff Spring 13 Part 1