Stream Ecology (NR 280)
Chapter 2 – Stream flow
The Water Cycle and Water Balance
Simple Stream Hydraulics
Measuring Stream Velocity and Discharge
Summarizing Stream Discharge
Distribution of the Earth’s Water
Fresh
Water (3%)
Other (0.9%)
Ground
Water
(30.1%)
Saline
(oceans)
97%
Earth’s
Water
Ice Caps
and
Glaciers
(68.1%)
Surface
Water
(0.3%)
Rivers (2%)
Swamps (11%)
Lakes
(87%)
Fresh Water
Fresh Water
(All)
(Available)
http://ga.water.usgs.gov/edu/waterdistribution.html
If ~half of Ground Water is available, then maybe ~0.75% of Earth’s Water is “available”.
The Water Balance
𝐺𝑎𝑖𝑛𝑠 − 𝐿𝑜𝑠𝑠𝑒𝑠 = 𝐶ℎ𝑎𝑛𝑔𝑒 𝑖𝑛 𝑆𝑡𝑜𝑟𝑎𝑔𝑒
𝑃 + 𝐺𝑖𝑛 − 𝑄 + 𝐸𝑇 + 𝐺𝑜𝑢𝑡 = ∆𝑆
𝐼𝑓 ∆𝑆 = 0
𝑃 + 𝐺𝐼𝑁 = 𝑄 + 𝐸𝑇 + 𝐺𝑜𝑢𝑡
𝑄 = 𝑃 + 𝐺𝑖𝑛 − 𝐸𝑇 + 𝐺𝑜𝑢𝑡
𝑄 = 𝑃 − 𝐸𝑇 + 𝐺𝑖𝑛 + 𝐺𝑜𝑢𝑡
𝑄 = 𝑁𝑒𝑡 𝑃𝑟𝑒𝑐𝑖𝑝𝑖𝑡𝑎𝑡𝑖𝑜𝑛 + 𝑁𝑒𝑡 𝐺𝑟𝑜𝑢𝑛𝑑𝑤𝑎𝑡𝑒𝑟 𝐼𝑛𝑝𝑢𝑡
Example Regional Water Balances
Allan and Castillo Fig 2.3
World Water Balance
(inches per year)
P = RO + Ev
RO = ROGW + ROSW
Even at this gross level of aggregation,
potential water resource problems are evident.
Images from the 1927 Flood
Colchester, Rt 15 and Ft. Ethan Allan in foreground, right
Downtown Montpelier
Champlain Mill, Winooski, city side
Photos: UVM Landscape Change Program
Why predict runoff?
• Estimate water supply (seasonal, annual)
• Estimate flood hazard, flood flows (eventbased)
• Design infrastructure – detention basins,
culvert sizing (“design storm”)
• Understand system behavior
Runoff Production
Precipitation rate, p (mm/hr)
Infiltration rate, i (mm/hr)
Horton overland flow (Robert E. Horton)
p > i  overland flow
time
Runoff Production
Horton Overland Flow
http://www.ceg.ncl.ac.uk/thefarm/
Kidsgeo.com
R5 Catchment, Oklahoma.
Photo: K. Loague, Stanford Univ.
Runoff Production
Variable Source Area model
(John D. Hewlett and later Thomas Dunne)
Ward & Trimble, Fig 5.3
Runoff Production
Variable Source Area model
Source: Taiwan Forestry Research Institute
http://oldpage.tfri.gov.tw/book/2000/23e.htm
Gaining and Losing Streams
Allan and Castillo Fig. 2.6
Water flows downhill
(…really, down potential)
ΔL
ΔH
ΔH/ΔL = hydraulic gradient, a
“pushing” force that can do work
Water flows downhill
(…and through the substrate if possible)
ΔL1
ΔH1
ΔL2
ΔH2
ΔL3
ΔH3
The hyporheic zone
Velocity Profiles in a Stream
Velocity is not uniform
Plan View
Depth (z)
0.2 * z
0.6 * z
0.8 * z
Width (w)
Side View
Use 0.6*z for z<0.75m
Use mean of 0.2*z and
0.8*z for z>0.75m
Velocity
Width (w)
Depth (z)
Velocity
Flow Dynamics
Source: USGS
Measuring Velocity
• Floating object
- Requires a correction factor
• Electromagnetic
• Direct current
• Acoustic Doppler, others
• pubs
oranges
rubber duckies
sontekcom
benmeadows.com
USGS
hachwater.com
Measuring Discharge
The Velocity-Area Method
Q = Flow area * Flow velocity
Q = Depth * Width * Velocity (Units: m*m*(m/s) = m3/s
Q = Σ (Di x Wi x Vi), over many subsections, i = 1 to n
For example: 0.2 m * 0.34 m * .09 m/s = .006 m3/s
Measuring Discharge
• Obtain Q measurements at
various stages
• Relate to Q to stage
• Fit a line or curve (may take
multiple fits)
• Apply equation to past or
future stage measurements
• Assumes relation between Q
and stage remains constant
Images: U.S. Geological Survey
• Labor intensive and therefore
expensive. Subject to change.
Challenges
tfhrc.gov
tfhrc.govusace.army.gov
• Taking measurements in
the exactly the same spot
is difficult
• The velocity-area method
is time consuming
• If the channel shape at the
“control section” changes,
so does the rating curve
Discharge Control Structures
V-notch weir
Parshall flume
Weir and Flume Equations
Rectangular weir
“V” notch weir
C and k = f(θ)
Q = C hn
where Q is in m3/s and h is in m
Coefficiens C and n are
computed as a function of
“throat” width, b.
Source: http://www.lmnoeng.com/Weirs/
Discharge (Gaging) Stations
Telemetry
Mechanical Float
and Recorder
Electronic pressure
transducer and data
logger
The Chezy, Manning, and
Darcy-Wesibach Velocity Formulas
We will explore these more in lab
2
𝑉 = 𝐶 𝑅𝑆
1.49 ∗ 𝑅 ∗ 𝑆
𝑉=
𝑛
3
1
2
V=Velocity (L/T)
C=Chezy Friction Coefficient (L1/2/T)
R = Hydraulic Radius (L)
S = Slope (L/L, dimensionless)
n = Manning’s Coefficient
g = acceleration of gravity (constant)
f = Darcy-Weisbach Friction Factor
𝑉=
8𝑔𝑅𝑆
𝑓
Modeling
HEC-RAS Modeling Software (US Army Corps of Engineers)
http://www.hec.usace.army.mil/software/hec-ras/index.html
Area Specific Discharge
10 km2 watershed
Avg. Flow = 17 m3s-1 / 10 km2
= 1.7 m3s-1/ km2
= 14.7 cm d-1
2 km2 watershed
Avg. Flow = 3 m3s-1/ 2 km2
= 1.5 m3s-1/ km2
= 12.6 cm d-1
The Hydrograph
Specifically, a storm hydrograph
Ward & Trimble, Fig. 5.11
Surface Water Hydrograph
Seasonal Water Table Hydrograph
Short-Term Water Table Hydrograph
Pembroke NH Well Hydrograph (Blow Up)
20-Jul-11
8.9
Water table depth (feet)
9
9.1
9.2
9.3
9.4
9.5
9.6
9.7
Time (hourly data in July and August 2011)
27-Jul-11
3-Aug-11
Lake Level Hydrograph
Factors affecting runoff
• Precipitation– Type, duration, amount, intensity
• Watershed Characteristics
– Size, topography, shape, orientation, geology, soils
• Land Cover and Land Use
– Forestry, wetlands, agricultural, urban density,
impervious area,
Stream flow (cubic feet per sec)
Impacts of Development on
Stormwater Quantity
• Higher highs/lower lows
• Intensification/flashiness
• Flow regime modification
Rainfall
Runoff - undeveloped
Runoff - developed
Runoff – “managed”
Time (hours)
Effect of Stream Order on Hydrograph
As flow accumulates, Rainfall
resistance to flow
causes the hydrograph
to spread (dispersion)
1st Order
and the peak flow is
increasingly delayed.
2nd Order
3rd Order
4th Order
Flow (Anything) Duration
• Obtain data series
(Any regular series)
• Rank in descending order
(Regardless of date)
• Probability of Exceedence
Pe = (rank#)/(max. rank + 1)
• Plot data vs Pe
# Data for the following site(s) are contained in this file
# USGS 04290500 WINOOSKI RIVER NEAR ESSEX JUNCTION, VT
# ----------------------------------------------------------------------------------#
#
agency_cdsite_no
datetime
cfs code
5s
15s
16s
14s
14s
USGS
4290500 1/25/1929
920 A
USGS
4290500 1/26/1929
890 A
USGS
4290500 1/27/1929
990 A
USGS
4290500 1/28/1929
1150 A
USGS
4290500 1/29/1929
980 A
USGS
4290500 1/30/1929
840 A
USGS
4290500 1/31/1929
730 A
USGS
4290500 2/1/1929
700 A
USGS
4290500 2/2/1929
600 A
USGS
4290500 2/3/1929
450 A
USGS
4290500 2/4/1929
850 A
USGS
4290500 2/5/1929
880 A
USGS
4290500 2/6/1929
910 A
USGS
4290500 2/7/1929
650 A
USGS
4290500 2/8/1929
590 A
USGS
4290500 2/9/1929
500 A
Extreme Events
The “Annual Maximum Series”
• Obtain data series
(Annual Maximum only)
• Rank in descending order
(Regardless of year)
• Probability of Exceedence
Pe = (rank#)/(max. rank + 1)
• Return interval is
RI = 1/Pe
• Plot data vs Pe or RI
#
# U.S. Geological Survey
# National Water Information System
# Retrieved: 2011-09-04 23:57:41 EDT
#
#
#
agency_cd
site_no peak_dt
peak_tm peak_va peak_cd gage_ht
5s
15s
10d
6s
8s
27s
8s
USGS
4290500
11/4/1927
113000
7
50.4
USGS
4290500
3/17/1929
19300
11.64
USGS
4290500
1/9/1930
21300
12.6
USGS
4290500
4/11/1931
22600
13.22
USGS
4290500
4/13/1932
23600
13.68
USGS
4290500
4/19/1933
34600
18.6
USGS
4290500
4/13/1934
31600
17.32
USGS
4290500
1/10/1935
30900
6
16.96
USGS
4290500
3/19/1936
45300
6
23.54
USGS
4290500
5/16/1937
26400
6
15.07
USGS
4290500
9/22/1938
34300
6
18.72
Water Use in
the US
(2000)
What is
“consumptive
use”?
Is it “small”
or “large”?
Fig 1.8 in Ward and Trimble
We often ‘use’ water without realizing it
1 automobile
400,000 liters
(106,000 gallons)
1 kilogram
cotton
10,500 liters
(2,400 gallons)
1 kilogram
aluminum
9,000 liters
(2,800 gallons)
1 kilogram
grain-fed beef
7,000 liters
(1,900 gallons)
1 kilogram
rice
1 kilogram
corn
1 kilogram
paper
1 kilogram
steel
5,000 liters
(1,300 gallons)
1,500 liters
(400 gallons)
880 liters
(230 gallons)
220 liters
(60 gallons)
Miller (2004)
Fig. 13.6, p. 298
We use more water than most
Environment Canada (http://www.ec.gc.ca/water/e_main.html)
The basic structure of water
The water molecule is a “dipole”
Water as a Solvent
S. Berg, Winona College
What happens to the water we use?
Ward and Trimble Table 1.7
Where does the used water go?
Discharge of untreated
municipal sewage
(nitrates and phosphates)
Nitrogen compounds
produced by cars
and factories
Discharge of
detergents
( phosphates)
Discharge of treated
municipal sewage
(primary and secondary
treatment:
nitrates and phosphates)
Lake ecosystem
nutrient overload
and breakdown of
chemical cycling
Dissolving of
nitrogen oxides
(from internal combustion
engines and furnaces)
Stormwater
Natural runoff
(nitrates and
phosphates
Manure runoff
From feedlots
(nitrates and
Phosphates,
ammonia)
Runoff from streets,
lawns, and construction
lots (nitrates and
phosphates)
Runoff and erosion
(from from cultivation,
mining, construction,
and poor land use)
Miller (2004)
Fig. 19.5, p. 482
Biological
Condition
(Phosphorus)
Biological
Condition
(Nitrogen)
Impaired
Rivers
Burton and Pitt (2002) Stormwater Effects Handbook
Impaired
Lakes
Burton and Pitt (2002) Stormwater Effects Handbook
Biological
Condition
(Taxa)
Why should we care?
• Drinking water
• Irrigation
• Contact (swimming, wading)
Friday, August 6, 2004
“U.S. beach closures hit 14year high - Unsafe water
caused by runoff, lack of
funding, report says”
• Recreation (fishing, boating)
• Waste purification
• Aesthetics
• Ecosystem integrity
Credit: Center for Watershed Protection