Lecture 2 hydrological and demand survey

Hydrological and demand survey (7hours)

 Plant factor and load factor,
 Hydrograph and flow duration curve,
 Hydrological cycle,
 Matching power supply with demand,
 Capability and demand survey,
 Methods of finding ADF (annual average daily flow),
 Methods of head measurements,
 Methods of flow measurements,
 load demand curves of various loads,
 Peak demand forecasting,
 Optimum generating installed capacity,
 Geological consideration.

Hydrograph
 A hydrograph is a graph showing the rate of flow (discharge) versus time past a specific point in a
river, or other channel or conduit carrying flow.
 It shows how flow varies throughout the year.
 It also help to know the time for which specific flow is available..
E.g. Discharge of 200 l/s is available only 9 months.

Exceedance Curve / Flow Duration Curve
 The FDC shows how flow is distributed over a period (usually a year).
 The vertical axis gives the flow,
 the horizontal axis gives the percentage of the year that the flow exceeds the value given on the y-axis.
How to convert hydrograph to FDC?
By taking all the flow records over many years and placing them the highest figures on
the left and the lower figures placed progressively over to the right.

Importance of Flow Duration Curve:
 FDC is more useful when calculating the energy available for a hydro-power
scheme.
 The FDC can immediately indicate the level of flow that will be available for at
least x% of the year (known as Qx).
 Helps in determining minimum and maximum flow.
 This is a useful planning tool, allowing a choice of size of turbine and indicates
required variable flow performance of turbine

Steep Flow
A steep flow duration curve is bad for micro-hydro. It implies a ‘flashy’
catchment – one which is subjected to extreme floods and draughts.
Factor which cause a catchment to be ‘flashy; are:
 Rocky, shallow Soil
 Lack of vegetation cover
 Steep, short streams
 Uneven rainfall (frequent storms, long dry periods)
Flat Flow
A flat flow duration curve is good because it means that the total annual flow will be spread more
evenly over the year, giving a useful flow for longer periods, and less severe floods.
Characteristics of a flat FDC are:
 Deep Soil
 Heavy vegetation
 Long, gently sloping streams
 Bogs, marshes
 Even rainfall ( temperate or two monsoons)

Compensation Flow
A portion of the flow, historically called the compensation flow (but now also referred to as the ‘residual’,
‘reserved’, ‘prescribed’ or ‘hands-off’ flow), may need to by-pass the scheme for aesthetic or environmental
reasons. In schemes where water is diverted from the main course of the river this compensation flow is needed
to maintain the ecology and aesthetic appearance of the river in the depleted stretch.

Hydrological cycle
The water cycle, also known as the hydrological cycle or the hydrologic cycle, describes
the continuous movement of water on, above and below the surface of the Earth

Load Factor
 The load factor is defined as the average load divided by the peak load in a
specified time period
𝐹𝐿𝐷 =
𝐴𝑣𝑒𝑟𝑎𝑔𝑒 𝐿𝑜𝑎𝑑
𝑀𝑎𝑥𝑖𝑚𝑢𝑚 𝐿𝑜𝑎𝑑 𝑖𝑛 𝑔𝑖𝑣𝑒𝑛 𝑡𝑖𝑚𝑒 𝑝𝑒𝑟𝑖𝑜𝑑
𝐹𝐿𝐷 =
𝐷 𝑎𝑣𝑔
𝐷 𝑚
 The higher the load factor is, the smoother the load profile is, and the more the
infrastructure is being utilized.
 The highest possible load factor is 1, which indicates a flat load profile.

Plant factor
 The ratio total energy consumed in a particular period to the maximum energy available from the
plant in the same period.
𝑃𝐹 =
𝑡𝑜𝑡𝑎𝑙 𝑒𝑛𝑒𝑟𝑔𝑦 𝑐𝑜𝑛𝑠𝑢𝑚𝑒𝑑 𝑖𝑛 𝑡𝑖𝑚𝑒 𝑇
𝑚𝑎𝑥𝑖𝑚𝑢𝑚 𝑒𝑛𝑒𝑟𝑔𝑦 𝑎𝑣𝑎𝑖𝑙𝑎𝑏𝑙𝑒 𝑓𝑟𝑜𝑚 𝑡ℎ𝑒 𝑝𝑙𝑎𝑛𝑡 𝑖𝑛 𝑡𝑖𝑚𝑒 𝑇
 Plant factor shows to what extent the energy available from the plant has been used.

Plant factor from Calculation of FDC

Importance of Plant factor
 The plant factor shows the extent of energy use from the available energy potential.
 A lower plant factor means less energy consumption, less revenue generated and a longer
payback periods which may even increase the plant cost. A plant factor of 0.4 in the initial
years and 0.6 or more in the subsequent years is desirable. Plant factor can be improved by
matching power supply and demand through a careful capability and demand survey.

Matching Power Supply and Demand
Matching the supply and demand is very important !!!
In the case that demand exceeds capacity
 Power shortages
 Downsize supply area
 Limit power usage
 In the case that demand is much less than capacity
 More costly than that of appropriate capacity
 Possible to extend the supply area
 Possible to introduce battery charging systems
 Possible to Encourage to introduce livelihood equipment

How To Match Power Supply & Demand?
 Decide what priority you give to each use of water.
 Consider how the water demand variation throughout the year compares
with water availability. To do this, prepare a demand/supply graph for a
typical year.
 Prepare a demand supply graph for a typical day.
 Calculate the plant factor considering only the primary loads.
 Calculate the plant factor with addition of secondary loads.
 Consider minimum down time and modify the plant factor accordingly.
 Calculate the unit energy cost and compare with other available
alternatives.

For example,
A micro hydro is proposed with following demand and supply data:
Gross head: 25 meters
Flow as shown in the hydro graph
Electrical lighting: 20 KW, 6pm to 12 pm
Milling: Miller desires 12 KW, but is ready to do with 6 KW if not possible, 8 am to 4 pm
Battery charging: 1 KW: anytime
Heat storage cookers: Only 10 villagers, 200 watts each: anytime
Irrigation demand: Water needed for 3 dry months, 400 hectares, each hectare needs 5 m3 per
day, demand will double within 4 years.
Is there enough water to satisfy this demand? If so will the proposed scheme be financially justified
against a diesel option offering a unit energy cost of 8 cents per kilo watt hour? Scheme Cost $40000
and 10% of the scheme as O+M cost

Step 1: Setting Priority
 Priority I: Irrigation
 Priority II: Lighting (20 KW from 6pm to12 pm)
 Priority III: milling (12 KW for 8 hrs from 8 am to 4 pm) : Primary loads
 Priority IV: Battery charging (noncommittal basis): Secondary loads
 Priority V: HS cookers (noncommittal basis): Secondary loads
Step 2: Is there enough water to satisfy all these demands?
Consideration of irrigation demand
Water requirement=5*400*2=4000 m3/day
Water availability=.160*3600*8 (8 hrs only are available in a day for irrigation)=4608 m3/day
Hence there is enough water to satisfy the irrigation demand as well.
Step 3: Prepare a demand supply graph for a typical day

Step 4: Plant factor for primary loads
={(20*6)+(12*8)}/(20*24)
=216/480
=0.45
Step 5: Plant factor considering the secondary loads(on yearly basis)
=0.45+{(0.5+2)*9 months}/(20*12months)
=0.54
Step 6: Modified plant factor considering 1 month breakdown time
=(11/12)*0.54
=0.5
Step 7: Per unit cost of micro hydro
=(4000+400)/(20*0.5*8760)
=5 cents/kWh which is less than per unit cost of diesel i.e. 8 cents/kWh
Hence micro hydro is financially justified

Capability and Demand Survey
Why?
To explore whether the scheme will be effectively managed over
its life in terms of tariff collection, maintaining financial accounts,
resolving conflicts, distributing welfare benefits etc. and to assess
the assistance required to raise capability of locals to required
level.
To explore what demand is there for a new scheme, how much
and where it is needed and in what form, whether there is
willingness and ability to pay and how would the new scheme
bring the benefit to less advantaged people and what are the
disadvantages of the scheme.

Items to be covered by Capability and Demand Survey(1)
 Map of village showing distances and position of house and possible future commercial activities
 Types of people and their comments on how the proposed scheme will affect their economic security and
opportunities in the future.
 Summary of institutions, organization etc who may help in financing the scheme.
 Description of current irrigation system and its management and future plans for irrigation and how people
expect hydropower to affect their irrigation system
 Assessment of capability of local organization to manage complex scheme involving finance, welfare
distribution, operation and machinery and maintenance of machinery

Items to be covered by Capability and Demand Survey(2)
 Interview notes from people/ institution
 Quantity of energy required, what for and when it is required
 Description of new appliances and the way how they are purchases, maintained and
operated
 Assessment of likelihood of effective and long lasting distribution of benefits from the
scheme to the poor member of the community.
 Recommendation for organizational precondition for raising capability of locals
 A plan for management system explaining how tariff and revenue would be collected

Selection of micro hydro sites

Methods of finding ADF (annual average daily flow)
Catchment Area
W
Y
Z
1
0
2
3

Steps:
1. Select a site for micro hydro.
2. Record the location of three rain gauge say W, Y, and Z. Let x, y and z be their annual average rainfall in
mm/yr.
3. Connect the rain-gauge location and bisect them to get a common point as shown in figure.
4. Find area covered by each rain gauge.
i. Area W = portion bounded by 1-0, 0-2 & catchment boundary,
ii. Area Y = portion bounded by 1-0, 0-3 & catchment boundary,
iii. Area Z = portion bounded by 2-0, 0-3 & catchment boundary.
iv. Total Area (Catchment Area) = Area W + Area Y + Area Z
5. Then the average rainfall in this catchment area is given by,
=(Area Z / Total Area) * z + (Area Y / Total Area) * y + (Area W / Total Area) * w
6. Find the runoff (mm/yr)
1. Runoff = Rainfall – Evaporation
2. Runoff by Rainfall_Runoff Graph
3. Runoff = 50% of Rainfall  Rough method
7. Volume of run off in mm3/yr = run off mm/yr * catchment area mm2
8. Finally, ADF= Vol. of run off in m3/s

NET Flow
Net Flow = ADF - ADFirrigation - ADFseepage

For an example:
In graph plot,
Area W=45squares
Area Y=40squares
Area Z=50squares
w=2000mm/yr
y=2500mm/yr
z=3000mm/yr
Scale of map: 1square-box=1mm2 and 1mm=300m
Total area = 45+40+50 = 135 squares
Average rainfall = (45/135)*2000+(40/135)*2500+(50/135)*3000
= 2518.52mm/yr
Run off in mm/yr = 50% of 2518.12 = 1259.26
Catchment area = 135 * 3002* 106 mm2
Volume of run off in m3/s = 135 * 3002* 106 * 1259 mm3/yr
ADF = (135 * 3002* 102 * 1259 * 10-9) / (365 * 24 * 60 * 60) m3/s = 0.49 m3/s

What to do in absence of Rain Gauge??
 If you have one or two year time to wait for planning and financial clearance, immediately install a flow
measuring device such as a notched weir into the stream, and monitor as frequently as possible.
 Setup and monitor at least one rain gauge in the region of interest.
 Do not use short-term records on their own, as two years’ data can be misleading (fifteen years’ data are
required) but correlate them with other data
 Consult a professional hydrologist.
 Use the flow correlation method.
 Often data in the form of isohyetal maps are available. These shows lines of constant rainfall. They
should never be used as a single indication of rainfall, but are sometimes useful as a check on other
indications. Should be avoided as catchment area is too small for accuracy.

Flow correlation method
assignment

Head
 Important parameter in designing micro-hydro
 Must be accurate (3% )
 Atleast measured by three separate method
Methods of Head measurement
 Water-filled tube (with rods or person)
 Water-filled tube and pressure gauge
 Sighting meters (Abney Level)
 Altimeter

Water- filled tube
 Useful for low head sites.
 Cheap and reasonably accurate
 Must repeat the process for good accuracy
 Easy to handle
 No need for skilled engineer.
 Relatively accurate.
Material Required:
Nylon Hose
Height Marker
Prepared Record Sheet

b. Using graded rods
i. Person Y measures height A1 at expect forebay surface level.
ii. Person Y stays in the same place and measures B1, just as person X has moved downhill and
measures A2
iii. Finally all heights are summed
H1=A1-B1
H2=A2-B2
H3=A3-B3
Hn=An-Bn
Head=H1+H2+H3+Hn

Builders’ levels
 Accuracy 1mm
 Expensive
 Heavy
 Slow
 Skill operator are needed
 Not suitable for steep, wooden sites.
theodolites
 Expensive
 Heavy
 Fast and accurate work where ground is clear.
 Slow on wooded sites and lots of error.
Note:
 Both requires calibration and re-calibration.
 Do not trust on borrowed theodolites. You must calibrate it again.

Methods of FLOW measurement
1. Velocity Area Method
2. Bucket Method
3. Salt Dilution Method
4. Weir Method

Float-Area Method
The amount of water passing a point on the stream channel during a given time is a function of
velocity and cross-sectional area of the flowing water.
Q = A*V
where Q is stream discharge (volume/time), A is cross-sectional area, and V is flow velocity
You need:
 tape measure
 watch or stop-watch
 rod, yard or meter stick to measure depth
 buoyant objects such as a weighted block of wood or oranges (objects that float immersed at the water
surface)
 stakes for anchoring tape measure to stream banks
 wader
Site Selection:
 straight section of stream
 uniform in grade
 minimum surface agitation

Lecture 2 hydrological and demand survey

Velocity
V = travel distance/ travel time
Because surface velocities are typically higher than mean or average velocities
V mean = k Vsurface where k is a coefficient that generally ranges from 0.66 to 0.75, depending on channel
depth.
Procedure:
 Choose a suitable straight reach with minimum turbulence (ideally at least 3 channel widths long).
 Mark the start and end point of your reach.
 If possible, travel time should exceed 20 seconds.
 Drop your object into the stream upstream of your upstream marker.
 Start the watch when the object crosses the upstream marker and stop the watch when it crosses the
downstream marker.
 You should repeat the measurement at least 3 times and use the average in further calculations.
Ex. Travel Distance = 50 feet 1st run = 34 sec.
2nd run = 32 sec.
3rd run = 28 sec.
k = 0.7
average run = 31.3 sec.
Velocity = (50 feet / 31.3 sec.) * 0.7 = 1.1 feet/sec.

Area
Area = average width * average depth
 Measure stream’s width and depth across at least one cross section where it is safe to wade.
 If possible, measure depth across the stream's width at the start and stop cross sections and average
the two but if only measuring one cross section choose the one downstream.
 Use a marked rod, a yard or meter stick to measure the depth at regular intervals across the stream.
 Five depth measurements are typical but more is better, especially in larger streams.
 Average your cross-sectional areas (A)
Using the average area and corrected velocity, you can now compute
discharge, Q.

Errors
 Error in Width
Minimized by taking segments at equal distances and the total surface width
be measured with more sophisticated instruments available now.
 Error in Depth
Minimized by taking segments at equal distances and the depth measured by
more sophisticated instruments available now.
 Error in Area Measurement
Minimized by correction of width and depth.
 Error in time measurement
 Error in length measurement
 Error in Mean Velocity at Verticals
Minimized by taking average velocity

BUCKET METHOD
Direct measurement with a bucket
Small river flow

The salt gulp or salt dilution method
The Salt Dilution Gauging method is a technique used for investigating the
discharge of turbulent rivers.
 Easy to accomplish
 Accurate (7%)
 Less time required (10 min)

EQUIPMENT
 Thermometer
 An Electrical Conductivity Meter
 A stick or apparatus to stir the solution
 Pure table salt (Sodium Chloride)
 A Bucket
PROCEDURE
 Decide on the amount of salt, and the distance between injecting the salt and monitoring
conductivity.
 Take a temperature reading of the stream and record it.
 Collect a bucket of water from the river and measure the natural conductivity and record it.
 Then add a known quantity of table salt to the bucket.
 Throw the bucket of solution into the river at approximately 20 times the width of the river
being sampled.
 Then measure the conductivity downstream and record the reading on the meter every 5
seconds until the reading stabilizes.
 Plot graph between Conductivity and time.

Example
In a flow measurement process using salt gulp method, 100 gram of salt was mixed with water in a
bucket and poured into the stream at a point which is 20 meter up from the location of the conductivity
meter. The readings of conductivity meter when plotted v/s time gave a total of 130 squares each square
being 5 second X 5 ohm -1 X 10-6.
If the temperature of water is 22 oC, find the flow of the stream in liter/sec.
Reciprocal of the conversion factor K-1 for 22 oC is 2.04X10-6 ohm-1/mgl-1.
Mass = 100 gm
Conversion factor =k=1/k-1
Area = no. of square * time *Conductivity

Examples of bad and good reading

Weir method
Q = C*L*H1.5
𝐶 = 1.838 1 +
0.0012
𝐻
∗ 1 −
𝐻
𝐿
1
2
10
Where,
Q = River flow (m3/s)
L:; Opening width of weir (m)
H: Overflow depth (m)

load demand curves of various loads
A graphical plot showing the variation in demand for energy of the consumers on a source of supply
with respect to time is known as the load curve.
If this curve is plotted over a time period of 24 hours, it is known as daily load curve . If its plotted for a
week, month, or a year, then its named as the weekly, monthly or yearly load curve respectively.
Commercial load

In general, the demand for electricity at night is bigger than that in the daytime.
The demand forecast is done for the nighttime.
Demand = Pr + Pp + Ld + α
where,
Pr: Power consumed by residents (kW)
Pr = Nh × ε × y × pr
where,
Nh: Number of households (HH)
ε: Households increase rate (HH/year)
y: Years considered (years)
pr: Power consumption per household (kW/HH)
= 0.1 ∼ 0.2 (kW/HH) in rural areas
Pp: Power consumed by public facilities (kW)
Ld: Loss over distribution line (kW)
= about 10% of power consumed
α: Other consumption for specific facilities
Demand Forecast

Optimum Generating Installed Capacity
All technical, economic and reliability indices are considered in a trade-off relation
for this purpose.
Using this approach, determine the annual energy potential by using flow duration
curve in different months.
Then, after specifying the income and costs of the plant, the economic indices of
different alternatives including all the benefits are extracted.
The reliability indices are then calculated.
Ultimately, through comparison of the technical, economic and reliability indices, a
superior alternative can be selected, determining the optimal installation capacity.

Geological Consideration
The visit to the proposed site should include a geological survey. It is aimed to return home with some
idea of the following:
Future Surface Movements: for example, loose rock slopes that may be disturbed by construction
work or by heavy rainfall, dry mud indicating mud flows, storm gulley's that may take torrents, and rock
flow during heavy rainfall, signs of flood behavior at valley base level;
Future Sub-surface Movements: for example, landslip and subsidence;
Soil and Rock types: information is a need in order to design the foundation of civil works, to decide
which materials to use in channel construction and to assess which building materials are available
on-site.

References
 Adam Harvey, “Micro-hydro design manual”
 Tri Ratna Bajracharya, “Mini and Micro Hydropower System
Design”
 Tokyo Electric Power Co. (TEPCO)
 khullabs.com

Lecture 2 hydrological and demand survey

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