irrigation water measurement and management

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by Engineer Imran Aziz Tunio

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By: haroon1470 (119 month(s) ago)

Handful information to understand the basics

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IRRIGATION WATER MEASUREMENT AND MANAGEMENT : 

IMRAN AZIZ TUNIO B.E (Civil), M.E (Hydraulics & Irrigation) IRRIGATION WATER MEASUREMENT AND MANAGEMENT

Importance of water management : 

Importance of water management Management of irrigation water helps in water conservation and efficient use. Inefficient use not only loss of the resources conserved but lead to waterlogging, and salinity. Growth of population needs more water for food and fibre,

Contd. : 

Contd. Increased the productivity of land to support the ever increasing population. Demand for water continues due to consumption for agriculture, industrial and municipal purposes.

Contd. : 

Contd. Demand increases that effects on supply, then Disputes among different users develop. Good management practice right from inception of the project is essential; otherwise,

Contd. : 

Contd. Farmers once accustomed to irrigate with plenty of water find it difficult to change their practice during periods of scarcity. Proper management ensures not only conservation of water, but also helps in increasing the productivity

OBJECTIVES OF MEASUREMENTS : 

OBJECTIVES OF MEASUREMENTS Most economic use of available water-crop per drop of water Reliable and efficient service to the users of the water Protection and maintenance of the irrigation networks

Definition of terms used : 

Definition of terms used Discharge: Discharge is a flow of water through any conveyance channel such as canal, distributary and watercourse etc. Its unit is cusecs. cusecs is defined as volume (cubic feet) of water flowing per second,(ft^3/s).

Contd. : 

Contd. (ii) Velocity: It is a speed of water that defines the distance covered by time taken (ft/sec). (iii) Depth: It is a vertical distance from water surface to bottom of channel, (ft). Gauge height: It is similar to depth (ft).

Contd. : 

Contd. Gross command area (GCA) Culturable command area (CCA) Water Allowance RD- reduced distance RL- reduced level Outlet Perimeter X section

Contd. : 

Contd. Free Flow Submerged flow Transitional flow Sub critical flow Critical flow Supercritical flow Control structures

Conversion : 

Conversion 1 m = 3.28 feet 1 in = 2.54 cm 1 cusec = 28.31 l/sec 1 Gallon = 3.78 litre (US) = 4.55 litre (UK) 1 litre = 0.001 m3 1 AF = 43560 sq ft 1 hectare = 2.47 acre = 10,000 m2

Water measurements methods : 

Water measurements methods Cutthroat Flume Current meter Float method Control structure method Gauge calibration

METHODS OF MEASUREMENTS:1. CUTTHROAT FLUME (CTF) : 

METHODS OF MEASUREMENTS:1. CUTTHROAT FLUME (CTF)

Cutthroat Flume : 

Cutthroat Flume

Steps for using CTF : 

Steps for using CTF Level CTF on bare ground by spirit level and scratch points where the level is checked Level CTF in watercourse by spirit level following scratches marked on it. Seal sides and bottom of CTF with hard soil so that no leakage should take place.

continued : 

continued Take readings of Hu and Hd in CTF after every 10 minutes until no change in water level take place Use final readings of upstream and downstream water depth in equation and find discharge.

Formulae used in CTF : 

Formulae used in CTF Free-flow nf Qf = Cf (Hu) Qf = Free flow discharge in cusecs, Cf = Free flow coefficient, nf = Free flow exponent, Hu = Upstream flow depth in ft.

Continued : 

Continued Submerged-flow nf Cs (Hu – Hd) Qs =------------------- ns (- Log S) Qs = Sub-merged flow discharge in cusecs, Cs = Sub-merged flow coefficient, Hd = Downstream flow depth in ft, ns = Submerged flow exponent, S = Submergence = Hu / Hd

Sizes of Cutthroat Flume commonly used in Pakistan : 

Sizes of Cutthroat Flume commonly used in Pakistan

Example:Find the discharge using the following observations in the Cutthroat Flume (CTF). : 

Example:Find the discharge using the following observations in the Cutthroat Flume (CTF).

2. CURRENT METER : 

2. CURRENT METER

Use of Current meter : 

Use of Current meter

Next slide: Use of current meter : 

Next slide: Use of current meter

Current meter (Contd.) : 

Current meter (Contd.)

Current meter (Contd.) : 

Current meter (Contd.) Divide total water surface width of cross section in at least 20-25 equal sub-sections (depending on width). Fix current meter at required position on its wading rod and count revolutions of current meter for specific time Find velocity with corresponding revolution and time from rating table

Current meter (Contd.) : 

Current meter (Contd.) Measure cross sectional area of flow at each sub-section (a1=b1*d1, a2=b2*d2, and so on) Determine discharge in each portion/part (q1=v1*a1, q2= v2*a2, and so on). Sum all discharges (q1+q2+…..+qn) and find total discharge (Q)

Example: Velocity measurements and discharge computation using current meter in the watercourse. : 

Example: Velocity measurements and discharge computation using current meter in the watercourse.

Example: Use of current meter : 

Example: Use of current meter

Flow measurements at outlet and its Calibration : 

Flow measurements at outlet and its Calibration

Steps to measure discharge at outlet: : 

Steps to measure discharge at outlet: Measure dimensions of outlet in feet. Measure head of water over the crest (H) in feet. Calculate discharge using the following formulae.

Empirical formulae of most commonly used outlets in Sindh : 

Empirical formulae of most commonly used outlets in Sindh Pipe outlet Q = CA (2gH)1/2 Open Flume Outlet Q = K B H1.5 APM or Jamrao Type Orifice Outlet Q = 7.3 B Y H 0.5

Notations : 

Notations Where, Q = Discharge through outlet in cusecs C = Coefficient of Discharge [for FF 0.6 to 0.7 and for SMF 0.74] A = Area of outlet ft2 Ho = Head of water over the pipe in ft ; H = Head of water over the crest of outlet in ft Bt = Width of Orifice in ft; Y = Height of Orifice in ft Hs = Depression head measured from the upstream water level to the top of the jet leaving an orifice [H-Y]

Table: Value of K in Open flume outlet : 

Table: Value of K in Open flume outlet

RATING CURVE / TABLE : 

RATING CURVE / TABLE Take 2-3 readings of (H) and measure discharges (Q) in the watercourse Select any one measurement of H and Q. Substitute value of H and Q in an appropriate equation and determine discharge coefficient (Cd), keeping exponent constant. (If B and Y of outlet is tampered then instead of Cd, K may be determined. K will be read as Cd*B*Y

Contd. : 

Contd. Use calculated coefficient in equation and find discharge from minimum to maximum values of H and put in tabulation form. Develop a curve between H and Q values “called as rating curve”.

Rating Table: : 

Rating Table:

Gauge Calibration : 

Gauge Calibration Measure four (4) discharge readings at approx. 100%, 80%, 60% and 40% of gauge heights. Measure water surface width (WT) and area of flow (A) of each sub section WT = WT1 +WT2 +WT3 -------WT30 A = A1+A2+A3-----------------A30 Where, and so on Determine hydraulic depth (DH) DH = A / WT

Channel losses : 

Channel losses Channel losses can be evaluated for most of the reaches in the irrigation network using the inflow-outflow method. In some reaches ponding test is to be conducted prior to or after the irrigation season Channel losses should be measured periodically The seepage loss rate is often expressed in m3/day per square meters of wetted surface area, which can be converted to mm/day

Channel losses : 

Channel losses Channel losses vary with water surface elevation

Seepage losses measurements : 

Seepage losses measurements Methods of seepage losses The Inflow-Outflow method The Ponding method, and

Inflow-outflow method: Difference in inflow and outflow is called seepage loss in channel. : 

Inflow-outflow method: Difference in inflow and outflow is called seepage loss in channel. The method is used for relatively long sections (one km or more), with no or few diversions (which should then also be measured or closed). It should be ensured that leakages (rat holes, cracks, etc.) are repaired before the measurements start so as not to mix up seepage losses and leakages.

Inflow-outflow method. Contd. : 

Inflow-outflow method. Contd. The water level in the canal should be kept constant during the measurements The actual inflow and outflow measurements should be done in straight canal sections, and not near any obstructions like bridges, regulators, etc.

Seepage loss measurements : 

Seepage loss measurements Seepage loss rate in lps/100m Ql = (Qu-Qd)/L Seepage loss rate in % /100m Ql = (Qu-Qd)/ QuL Seepage loss rate in mm/day Sl = [8.64 (10) 7 (Qu-Qd)]/WPavg L

Seepage loss example: Left main canal (LMC) : 

Seepage loss example: Left main canal (LMC)

Water losses in watercourse : 

Water losses in watercourse LOSS CALCULATION Where: mg=moga; h = head reach; m = middle reach and t = tail reach.

Ponding method : 

Ponding method

Ponding Test : 

Ponding Test

Ponding Test : 

Ponding Test

Ponding Test : 

Ponding Test

Ponding method: ExampleSeepage rate= 24* (WSD*WSWavg)/(WPavg*hrs of run) : 

Ponding method: ExampleSeepage rate= 24* (WSD*WSWavg)/(WPavg*hrs of run)

Approximate Seepage losses from canals : 

Approximate Seepage losses from canals Type of soil Seepage loss (m3/m2/ day) “Impervious” clay loam 0.07-0.10 Clay loam 0.15-0.23 Sandy clay 0.23-0.30 Sandy loam 0.30-0.45 Sandy soil 0.45-0.55 Pervious gravelly soil 0.75-0.90

OPERATION : 

OPERATION Monitoring of system Daily gauges and discharge Daily gauges at tail of distributary (1.0 ft at crest of outlet ) Discharges--- head – middle and tail of channel

Operation (contd.) : 

Operation (contd.) H-Register Depth of water above crest of outlet “called H”. Observations required to record at site in a module book and later transfer to H-register. Irrigation Register This includes outlets as well as dehs information and that is being sent by Abdar to the SDO at end of each crop season.

Operation (contd.) : 

Operation (contd.) Outlet Register Outlet register (called form-100) give the sanctioned discharges and other design data of each outlet based on the CCA and the water allowance per 1000 acres.

Operational Characteristics of canal System : 

Operational Characteristics of canal System Reliability (arrival of water according to schedule); Equitable distribution; Efficient supply (minimization of canal losses); Accountability, and discipline in distribution and use of water;

Standard Performance levels of the System [According to Molden and Gate 1990] : 

Standard Performance levels of the System [According to Molden and Gate 1990]

MAINTENANCE : 

MAINTENANCE An effective maintenance components: Routine maintenance Preventive maintenance Seasonal maintenance

Maintenance (contd.) : 

Maintenance (contd.) Annual maintenance Unscheduled maintenance and Emergency maintenance.

SURVEY SHEET FOR WATERCOURSE INFORMATION : 

SURVEY SHEET FOR WATERCOURSE INFORMATION NAME OF DISTRIBUTARY: OFFTAKING CHANNEL: WATERCOURSE NUMBER: DATE:

ON FARM WATER MANAGEMENT SITUATION ANALYSIS CHECKLIST : 

ON FARM WATER MANAGEMENT SITUATION ANALYSIS CHECKLIST LAYOUT OF WATER COURSE AND FIELD LOCATION a. Mapping of watercourse (main and branches) b. Position/location of existing turnouts (Nakkas) and fields VISUAL IDENTIFICATION OF CRITICAL AREAS AND PROBLEMS a. Deteriorated portions of watercourse i) perceived by farmers ii) perceived by technical staff b. Fields causing backflow and overtopping in watercourse

VEGETATION AND TREES ON THE WATERCOURSE : 

VEGETATION AND TREES ON THE WATERCOURSE location of trees obstructing the flow of watercourse Head: Middle: Tail: Plantation along the watercourse HIGH : MEDIUM: LOW: Uses of trees: Reasons for not cutting General condition of vegetation in watercourse

FARMERS PARTICIPATION IN MAINTENANCE OF WATERCOURSE : 

FARMERS PARTICIPATION IN MAINTENANCE OF WATERCOURSE Cleaning and de-silting Banks improvement and compaction Alignment ASSESSMENT OF WATER LOSSES Head Middle Tail ADDITIONAL SOURCES OF WATER Tubewells others

PROBLEM REGARDING IRRIGATION : 

PROBLEM REGARDING IRRIGATION Water scarcity Rotation Right of way Ownership Human and animal activity rodents

Slide 65: 

Good Luck From, I.A.Tunio

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