Chapter 4 Surface Runoff and Flow Measurement 2024.pdf

Chapter 4: Surface Runoff and Flow
Measurement
(5 hours)
Prof. Dr. Hari Krishna Shrestha
Contact: hari.k.shrestha@gmail.com
Last update: April 18, 2024
Chapter 4: Surface Runoff and Flow Measurement (5 hrs) (17%)
1. Drainage basin and its quantitative characteristics
2. Factors affecting surface runoff
3. Rainfall-runoff correlation (linear)
4. Stream gauging, selection of site, types of gauges and their selection
5. Stream flow measurement
1. Velocity area method, current meters, floats, velocity rods & dilution
techniques
2. Slope area method
6. Development of rating curve and its uses

4.0 Surface Runoff- Process
• Precipitation
• Infiltration
• Percolation
• Sub-surface flow
• Interflow
• Surface flow – runoff
• Sheet flow
• Concentrated flow – rivulet, brook, stream, river

Precipitation
Interception
Evaporation
Transpiration
Stem Flow
Runoff
Throughfall
Infiltration Subsurface Flow
Evaporation
Uptake
Runoff
Streams
Rivers

4.1 Drainage Basins and its Quantitative Characteristics
• A drainage basin (river catchment) is an area of land drained by a river and its
tributaries; when it rains in this area, the water goes towards the main river and
ends up at the river’s mouth.
• Quantitative Characteristics:
1. Catchment area and hypsometric curve
2. Catchment Centroid (x, y) in degrees/meters or northing/easting, z in meters (mamsl)
3. Catchment Slope, maximum and minimum elevations of the catchment divide
4. Land use/Land Cover (LULC) and local depression areas
5. Average infiltration for different return-period rainfall events, and Runoff Coefficient
6. Length and Slope of the Main River and major tributaries
7. Drainage Density and order of the tributaries
8. Surface soil type and the area of each soil type
9. Spatial distribution of rainfall in the catchment
10. Time series data of rainfall in the catchment (average, maximum and minimum)
11. Evapotranspiration from the catchment
12. Time series data of radiation, temperature, humidity, pressure, and wind speed
13. Intensity-Duration-Frequency and Depth-Area-Duration curves of the catchment
14. Groundwater recharge rate and volume in the catchment
15. Long term flow, peak flood flow, minimum flow from the river mouth of the catchment
16. Sediment type and discharge of each sediment type out of the catchment
Additional info: https://www.youtube.com/watch?v=jPF8oXSEx4s&ab_channel=learnsomethingtoday
http://www.ijstm.com/images/short_pdf/1415296455_P39-50.pdf

4.2 Factors Affecting Surface Runoff
Kaligandaki River

The braids on the Yarlung Tsangpo (Brahmaputra) near Lhasa before it enters a series of gorges
where the world's largest hydroelectric plant is being built by China.

4.2 Factors Affecting Surface Runoff
• Catchment factors
• Basin size, shape, slope
• Nature of the valley: wide, narrow
• Elevation
• Drainage density
• Infiltration factors
• Land-use and land-cover
• Soil type & geological conditions
• Depression storages
• Channel characteristics
• Cross section
• Roughness:
– river bed, river banks
• Storage capacity
Meteorological Factors:
• Storm Characteristics
• Initial loss
• Evapotranspiration
Catchment
Basin

4.3 Rainfall-Runoff Correlation (linear)
• Various forms of rainfall-runoff relations can be
developed based on specific rainfall and associated
runoff data
• Linear relationship: Q = a P + C
• Non-linear relationship: Exponential/Power/
Polynomial
– Q = discharge (weekly, monthly) from Direct Runoff
Hydrograph
– P = Precipitation

4.3 Rainfall-Runoff Correlation
Linear type relation
• R = a P + b; R = runoff, P = precipitation, a and b are linear regression constants
• a = [N(PR) – (P)(R)]/[N(P2)-(P)2]
• b = [R – a(P)]/N
• 𝑟 =
[N(PR) – (P)(R)]
[N(P2)−(P)2] [N(R2)−(R)2]
; 𝑟 = 𝑐𝑜𝑟𝑟𝑒𝑙𝑎𝑡𝑖𝑜𝑛 𝑐𝑜𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑡
Exponential type relation
• R = Pm or
• ln R = m ln P + ln 
Multiple Regression
Y = b0 + b1 x1 +b2 x2 + b3 x3 + b4x4
Y = runoff, x1 = baseflow, x2 = autumn precipitation, x3= snow water equivalent, x4 = spring
precipitation, and bi = regression coefficients.
Unless base flow can be separated and effect of snow melt can be established (if applicable),
the relation between daily data cannot be made. Normally relation between monthly, seasonal
or annual data is made. The ratio of runoff to rainfall is Runoff Coefficient.
Steps:
Convert weekly/monthly/annual flow into depth or volume.
Convert precipitation into depth or volume.
Plot the data and find the relation using appropriate regression method.

https://www.researchgate.net/publication/3190
37166_Water_balance_study_of_Beas_river_Hi
machal_Pradesh_using_ARCGIS_technique_upt
o_Pong_dam/figures?lo=1
Similar Rainfall-
Runoff Relationship
are established on
monthly or seasonal
basis to quickly
estimate the runoff
from rainfall data.

Chapter 4 Surface Runoff and Flow Measurement 2024.pdf

4.4 Stream Gauging(site selection, gauge type)
Runoff gauged indirectly through staff gauging (stage monitoring).
Gauge Type:
A) Discreet (Non-recording)
• Staff Gauge
• Sectional Staff Gauge
• Crest Gauge
B) Continuous (Recording)
• Laser/Radar Gauge (RLS)
• Automatic Staff Gauge
• Pressure Gauge
• Bubble Gauge
Continuous data required for generation and analysis of hydrograph.
The updated number of rivers and rivulets in Nepal, Energy Development
Commission (June 2016), is 11614.
http://www.renewableenergyworld.com/articles/2016/06/nepal-seeks-investors-for-
10-gw-of-electricity-by-2026.html

Sample annual gauge
river gauge versus date/year
0
100
200
300
400
500
600
700
0
200
400
600
800
1000
1200
1400
2017/
Jan
2017/
Apr
2017/
Jul
2017/
Oct
2018/
Jan
2018/
Apr
2018/
Jul
2018/
Oct
2019/
Jan
2019/
Apr
2019/
Jul
dail;y
Rainfall
[mm/day]
Discharge[m
3
/s]
rain
obs.Q by H-Q
calc.Q
Measured Q
Snow Depth
0
100
200
300
400
500
600
700
0
200
400
600
800
1000
1200
1400
2005/
Jan
2005/
Apr
2005/
Jul
2005/
Oct
2006/
Jan
2006/
Apr
2006/
Jul
2006/
Oct
2007/
Jan
2007/
Apr
2007/
Jul
2007/
Oct
2008/
Jan
2008/
Apr
2008/
Jul
2008/
Oct
dail;y
Rainfall
[mm/day]
Discharge[m
3
/s]

This technology is gradually getting obsolete, replaced by radar/laser water level sensors.
However, its use for the calibration purpose is still intact.

This technology is gradually getting obsolete, replaced by radar/laser water level sensors.

This technology is gradually getting obsolete, replaced by radar level sensors (RLS).
Bubble Gauge

RLS for continuous river gauging RLS at Rui Khola, Chitwan for EWS

4.4 Stream Gauging (Stage Monitoring)
staff gauge, sectional staff gauge, automatic staff gauge: pressure type, float
type, laser
Staff and Crest Gauge
Automatic Gauge recorder Automatic Gauge recorder
Laser type Automatic Gauge recorder
Crest Gauge

The U.S. Geological Survey (Rantz et al., 1982) have developed nine criteria for an "ideal" gaging
site. The criteria are:
1. The stream course is straight for about 300 feet upstream and downstream of the gage site.
2. At all stages, the total flow is confined to a single channel. There is also no subsurface or
groundwater flow that bypasses the site.
3. The streambed in the vicinity of the site is not subject to scour and fill. It is also free of
aquatic plants.
4. The banks of the stream channel are permanent. They are free of brush and high enough to
contain floods.
5. The stream channel has unchanging natural controls. These controls are bedrock outcrops or
stable riffle for low flow conditions. During high flows, the controls are channel constrictions or
a cascade or falls that is not submerged at all stages.
6. At extremely low stages, a pool is present upstream from the site. This will ensure the
recording of extremely low flows and avoid the high velocities associated with high stream
flows.
7. The gaging site is far enough removed from the confluence with another stream or from tidal
effects to avoid any possible impacts on the measurement of stream stage.
8. Within the proximity of the gage site, a reach for the measurement of discharge at all
stages is available.
9. The site is accessible for installation and operation and maintenance of the gaging site. The
selection of a gaging site is again a compromise between these criteria.
4.4 Site Selection (for establishing gauge site)

Site Selection (for establishing gauge site)
Characteristics of an ideal site for river gauging:
Parameter Reason
Straight reach
No turbulence
No drops
No sharp bends
No backwater effect
Accessible/visible
No direct impact from flow
Stable water surface
Stable cross section
Stable river bed

4.5 Stream Flow Measurement by V-A methods
4.5.1 Current Meter: vertical axis, horizontal axis
4.5.2 Surface Float
4.5.3 Velocity Rods
4.5.4 Dilution (salt dilution)
• Hydraulic Structures
• Electromagnetic
• Acoustic Doppler Current Profiler
(ADCP)

← Vertical Axis Current Meter
Horizontal Axis Current Meter ↓
4.5.1 Current Meters

4.5.1 Stream Flow Measurements: Cup type current meter

Stream Discharge Measurements using cup-type current meter
Head phone to count number of revolutions Lead weight to keep hand-line vertical and
current meter stationary
Cable car for Q measurement in bigger rivers Stilling well for stage hydrograph

Stream Discharge Measurements
Winch to control position of cable car
A-frame to elevate cable of cable car
Surface velocity measurement

Acoustic Doppler
Current profiler
(ADCP)

Discharge (m3/s, cumec)
• Discharge = cross sectional area of flow × average river flow velocity
• Q = V × A [unit: m2 * m/s = m3/s] cusec?
V = ƒ (number of rotation, time) (traditional cup-type or propeller type
current meter); higher the velocity higher the rotation speed
Stream Flow Measurement methods (Direct and Indirect):
• Current Meter: vertical axis, horizontal axis (based on the axis along
which the cups/blades of current meter rotates)
• Surface Float: Average flow velocity = surface velocity * K
• Chemical – dilution, salt dilution: mostly for small rivers with high
turbulence. Why?
• Electromagnetic
• Acoustic/Acoustic Doppler Current Profilers (ADCP)
• Hydraulic (or gated) Structures: Q = ƒ (h) = C hn (weir/ notch)
• Slope Area Method (Section 4.6)

Some newer types of current meters display the flow velocity directly, without having to
count the number of revolutions. However, regular calibration of the current meters is
needed to ensure accuracy of the discharge measurement.

Total Discharge = 7.065 m3/s
Total area = 20.6 m2
Average Velocity = 0.343 m/s

Distance
from bank
(m)
Width
W(m)
Effective
Width (m)
Depth
(m)
Revolutio
n
Time
(sec)
Area
(m2)
Velocity
(m/sec)
Discharge
(m3/sec)
0.0 0
0.6 0.6 0.675 1 15 50 0.675 0.29 0.196
1.2 0.6 0.70 4 39 55 2.8 0.674 1.887
2.0 0.8 0.90 5.5 50 50 4.95 0.85 4.208
3.0 1 0.90 6.5 56 50 5.85 0.946 5.534
3.8 0.8 0.75 4.5 39 50 3.375 0.674 2.275
4.5 0.7 0.60 2.5 35 50 1.5 0.61 0.915
5.0 0.5 0.602 1 20 50 0.602 0.37 0.223
5.6 0.6 0 0
19.75 0.77 15.237
Effective width (1st) = (W1 + (W2/2))2/(2W1)
Effective width (last) = (Wn+ (Wn-1/2))2/(2Wn)
V = aN+b, a = 0.016, b = 0.05
Average (stream flow) velocity = Q / A
Numerical example of a stream discharge measurement calculation.

V= a N + b
a = 0.0113; b = 0.0059
N= no. of revolution in 60 sec
(in this example)

Sample Discharge measurement and
calculation sheet.

4.5.2 Stream Flow Computation by Slope Area Method
https://pubs.usgs.gov/twri/twri3-a2/pdf/twri_3-A2_a.pdf
https://www.yourarticlelibrary.com/water/river-training/slope-area-method-concept-and-selection-of-reach/60961
Indirect method of flow estimation, assuming uniform flow, using Manning’s Formula
Energy equation:
Z + y = h (water surface elevation above the datum; hL = hf + he
ℎ1 +
𝑣1
2
2𝑔
= ℎ2 +
𝑣2
2
2𝑔
+ ℎ𝑒 + ℎ𝑓 → ℎ𝑓 = ℎ1 − ℎ2 +
𝑣1
2
2𝑔
−
𝑣2
2
2𝑔
− ℎ𝑒
𝑍1 + 𝑦1 +
𝑣1
2
2𝑔
= 𝑍2 + 𝑦2 +
𝑣2
2
2𝑔
+ ℎ𝐿
ℎ𝑓
𝐿
= 𝑆𝑓 = 𝑒𝑛𝑒𝑟𝑔𝑦 𝑠𝑙𝑜𝑝𝑒 =
𝑄2
𝐾2
; 𝐾 = 𝑐ℎ𝑎𝑛𝑛𝑒𝑙 𝑐𝑜𝑛𝑣𝑒𝑦𝑎𝑛𝑐𝑒 =
1
𝑛
𝐴𝑅 ൗ
2
3
Average K for the reach = (k1*k2)0.5
hf = fall + (V1
2/2g - v2
2/2g) when he ≈ 0
ℎ𝑒 = 𝐾𝑒
𝑉1
2
2 𝑔
−
𝑉2
2
2 𝑔
Ke = 0.3 for gradual expansion and
0.1 for gradual contraction

During a flood flow the depth of water in a 10m wide rectangular channel was found to
be 3.0 m and 2.9 m at two sections 200 m apart. The drop in the water-surface elevation
was found to be 0.12 m. Taking Manning's coefficient to be 0.025, estimate the flood
discharge through the channel.
L = 200m W = 10m
h1 = 3m h2 = 2.9m
head loss= 0.12m Manning's n = 0.025 Flood discharge = ?
A1 = 30 A2 = 29 A = W h
P1 = 16 P2 = 15.8 P = W + 2 h
R1 = 1.875 R2 = 1.835 R = A/P
K1 = 1824.7 K2 = 1738.9 K = (1/n) A R2/3
Average K for the reach = (k1*k2)0.5 = 1781.3
hf = fall + (V1
2/2g - v2
2/2g) = 0.12 + (V1
2/2g - V2
2/2g)
Trial hf Sf Q V1
2/2g V2
2/2g hf
1 0.12 0.00060 43.63 0.1078 0.1154 0.1124
2 0.1124 0.00056 42.23 0.1010 0.1081 0.1129
3 0.1129 0.00056 42.32 0.1014 0.1086 0.1129
Note: hf value for Trial 1 is assumed to be same as head loss value of 0.12m. For
subsequent trials, it is copied from the last column. The final Q value is achieved
when hf values does not change.

4.6 Rating Curves and
its Uses
• Rating Curve: relationship
between stage and discharge
• Developed by conducting a
series of stream discharge
measurement
• The curve can change if the
cross section of the river change
due to scouring, river bed
aggradation, or bank cutting
Hysteresis in rating curve: different discharge for same gauge
height and vice versa, When a flood wave propagates through a river
corresponding to same stage higher discharges are observed during
rising stage than in falling stages resulting in looped rating curves. This
affect is popularly known as hysteresis in stage–discharge relationship

Data to plot rating curve of a river
SN Discharge GH
1 40.604 1.94
2 54.55 2.11
3 59.84 2.14
4 62.005 2.18
5 73.688 2.28
6 76.06 2.27
7 80.112 2.29
8 86.485 2.40
9 89.808 2.44
10 100.621 2.53
11 116.85 2.64
12 129.443 2.73
13 155.85 2.92
14 221.501 3.28
15 559.32 3.80
16 599.478 4.00
17 654.761 4.40
18 919.534 5.28
GH= 0.6453Q0.2946
R² = 0.9831
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
6
0 100 200 300 400 500 600 700 800 900 1000
G.H
(m)
Discharge (m3/sec)
GH= 0.6453Q0.2946
R² = 0.9831
1
10
1 100
G.H
(m)
Discharge (m3/sec)

4.6 Uses of Rating Curves
• Convert stage into discharge
• Flood Disaster Risk Management: Early Warning
System
• Flood inundation area demarcation
• Gate operation in water resources development
(WRD) projects (hydropower/Irrigation, …)
• Sediment diversion during flood events
• Monitoring minimum flow release from WRD
projects for navigation and socio-cultural and
environmental uses.

Discuss the practical uses of rating curve of a river section. How is a rating curve
developed? Why a same river section can have multiple rating curves?
Taking the rating of current meter as V = 0.03 + 0.8 N, where V is in m/sec and N is the
number of revolutions/sec, compute the stream flow (Q) from the given data. If the rating
curve of the river section can be approximated by log Q = 1.1 log S + 0.2, calculate the
discrepancy % in measurement, given the river stage (S) during flow measurement is 1.6 m.
Distance from bank (m) 0.0 0.6 1.5 2.5 5.0 7.0 7.5
Depth (m) 0 0.3 0.75 1.2 1.2 0.3 0
Revolution 0 9 25 15 30 16 30 16 5 0
Time (sec) 0 45 90 80 100 90 100 80 40 0

(h) What are the reasons for a hysteresis loop in a rating curve of a river section?
(i) Discuss the role of infiltration capacity index in determining the excess runoff depth from
precipitation data.
(k) Given the stage (GH) versus discharge (Q) data, develop a rating curve equation and
calculate the discharge when GH = 3.5 m.
GH
(m)
1.94 2.11 2.14 2.18 2.28 2.27 2.29 2.40 2.44 2.53 2.64 2.73 2.92 3.28 3.80 4.00 4.40 5.28
Q
(m3
/s)
40.60 54.55 59.84 62.00 73.69 76.06 80.11 86.48 89.81 100.6 116.8 129.4 155.8 221.5 559.3 599.5 654.8 919.5

Expected skills from this chapter:
1. Develop rainfall-runoff relation (equation) from a set of rainfall and runoff data.
2. Stream discharge measurement using a current meter.
3. Calculate stream discharge from discharge measurement data (distance from edge,
depth, number of revolutions and time).
4. Develop rating curve from given set of stage and discharge data, using MS Excel’s
Solver facility.

Chapter 4 Surface Runoff and Flow Measurement 2024.pdf

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