Operational concept

Main canal structure

Function of structure

Advantages

Disadvantages

Application or design notes

Practice to improve operation

Project and country

1. FIXED UPSTREAM CONTROL

Proportional dividers

Divide incoming flow into predetermined (and generally fixed) proportions at each bifurcation point.

· No gate movements needed.
· No communications required.
· No decisions needed by operators.
· Less silt deposited in main and secondary canals than with other methods because of flow.

· Theoretical equity is not actually achieved because it is virtually impossible to design and install outlets so that they function as predicted over a range of flows.
· Even if outlets are precisely designed and installed correctly, hydraulic conditions would change over time (situation, changing cross sections, changing roughness) yet system can not be adjusted to match changes.
· If anything unexpected happens, there is no ability to respond.
· Water levels in canals fluctuate greatly with flow-rate changes, causing lining damage and often putting some offtakes above water level.

In warabandi of NW India and Pakistan, lower branches may be ungated and use a right rotation.

In Bali, Nepal and Fayoum (Egypt) project are pure flow division.

· If proportional control is needs for rotation farther down the system, main and secondary canals should still be operated with improved control methods to avoid disadvantage listed.
· Assumption that simple, nonadjustable proportional control will prevent tampering ignores reality that adjustments must be made over time to fine-tune any changing hydraulic parameters in order to achieve quality.

· Numerous, NW India and Pakistan

2. GATED UPSTREAM CONTROL

- with flow-level control

· Typically sluice or radial gates.
· Manual operation

Structure should maintain a constant water level. Instead, operators are instructed to use structure as flow-control devices.

None

This is a very common misapplication of upstream control. Operators are asked to do the impossible: with upstream control a constant flow rate cannot be obtained both through the turnout and the check structure.

- with water-level control

· First gate, inlet to canal (and generally an undershot or orifice-type gate) controls flow into canal.
· No other check structures and control flow; they control upstream water level.
· All structures are independently controlled.

· Low initial cost relative to more modern control techniques.
· Operation instructions for structures in main canal should be extremely simple: just keep upstream water level constant.

· Flows must be known in advance and be controlled at inlet all outlets to minimize tailender problems.
· Excellent person-to-person communications needed among canal operations if deliveries have flexibility in order to adjust the turnouts (offtakes) from the main canals.
· Tailender problems are pronounced.

· Suitable for arranged deliveries, rotations or proportional control from tertiary canals.
· 1-2 day delivery flexibility to offtakes (tertiary canals) is only possible if single canals are shorter than about 50 km, unless large buffer reservoirs are used throughout the system.

· Install buffer (balancing) reservoir throughout system.
· Have large canal section; use special head-insensitive turnout design to allow pool storage to be varied for operational flexibility.
· Install remotely monitored water-level sensors at tailends of canals and buffer reservoirs.

- with structure for manual operation

· Sluice gates (underflow).
· Motorized manual movements

· Large forces required to move the gates.
· Often stick in place and become inoperable.
· Hourly adjustment needed.
· U/S head varies greatly with change in flow, resulting in changing turnout flow rates.

Use side weirs with constant split (back into the canal) to reduce number of gate movements.

· Radial gates (underflow).
· Motorized manual movements

· Small forces required to move them if counter-balanced; they do not stick easily.

· Hourly adjustments needed.
· Upstream head varies greatly with change in flow.

· Use several smaller parallel gates rather than a few large gates.
· Use side weirs with constant spill (back into canal) to reduce number of gate movements.

· Rio Sinaloa and Yaqui, Mexico

Stoplogs

· Only a few minor changes needed per day. Upstream head varies much less with change in flow than if underflow gate is used.

· Stoplogs may be stolen for firewood.
· Stoplogs can become stuck and if too large can be difficult to remove and replace.
· Often the walkway above the structures unsafe for the operator.

· Use stoplogs with maximum dimensions of 2m x 5cm x 10 cm to facilitate handling.
· Construct a very stable catwalk for operator convenience and safety.

· Madera ID, California and many western districts, USA

Long-crested weirs

· Upstream head variations during a day may be almost negligible.
· Almost no operator intervention needed.
· Extremely simple.

· Do not allow for different controlled water during different flow regimes; will silt up unless underflow gates are provided at downstream ends.

Maximum effective design length is a about 8-10 times the channel width.

· Install underflow gates at downstream points in each structure to flush silt through the structure.
· Adjust the opening of underflow gates if major flow-rate changes occur in canal to minimize the upstream head variation.

· Mocanbinho, Brazil
· Mac Tang, Thailand
· Kemubu, Malaysia
· Coello, Colombia

- with structures for automatic operation

Automatic electrical controls, undershot or overshot gates

· Able to maintain very precise upstream water levels automatically
· Target depth can be changed

· Power outages or poorly trained or supplied maintenance personnel will result in failure.
· Preventive maintenance is crucial.
· Sometimes controllers are too complicated for operators (and maintenance personnel) to understand and adjust.
· If control program is not correct, gates will cycle badly, especially if installed in series.

· Can be motored and controlled remotely in case target depth is changed, or in an emergency.
· Make certain that controllers can be adjusted in field and have manual (electrical) over-ride.
· Gates must also be movable by hand if electricity fails.

· Use industrial-grade controllers and water-level sensors.
· Only use equipment and programs with a proven history of success.
· Use side weirs with continuous overflow if gates are undershot. Only move one gate at a time (if several gates are parallel at a site).

· Munda, Malaysia
· Friant-Kern Canal, California, USA
· Imperial ID, California, USA.

Hydraulic constant upstream level gates

· Very simple.
· Almost no maintenance.
· For some types, no adjustments are needed after initial installation.
· Sturdy and reliable.

· May be grater initial cost than electrically controlled automatic gate.
· Water-level control is within a design decrement (does not have the precision of control of electrical controllers).
· Target (controlled) water depth cannot be changed on many of these gates.

· Decrement can be reduced if small gates are used in parallel rather than one large gate

· To reduce prince, install one automatic gate in parallel with some manual gates. Manual gates can be adjusted for large flow-rate changes; hydraulic gate can handle daily or hourly fluctuation.

· Sorraia, Portugal
· Benil Amir, Morocco
· Dudly ridge WD, California, USA

3. DOWNSTREAM CONTROL WITH TOP LEVEL CANALS

· Gates always automatic
· Either electric or hydraulic

· Maintains a constant water level immediately downstream of gates there by supplying flow into downstream pool, as needed.
· For ordinary operation, flow rates into and through the main canals may not be known.
· Flow rates may be checked to see if there are capacity problems.

· Offtakes can be shut off or flow reduced at any time without advance notice.
· Very simple, reliable operation of main canal system.
· In effect, this method of operation puts a reservoir at each tertiary or distributary canal.
· Tailender problems are eliminated.

· Longitudinal slope should generally be less than 0.0003.
· Higher construction costs than upstream-controlled canals because of large cross-section needed and level tops.
· Operators of offtakes from these canals must generally be very responsible, or they will withdraw more water than canal can supply. If capacity of main canal is sufficient, this is not a problem.

· Demand operation of main and secondary canals is not to be confused with on demand deliveries to individual farmers, chaks, or watercourses.
Those deliveries are generally still scheduled or may even be operated on rotation.
· The need for human communications to operate main and secondary canals is almost eliminated.

· Turnouts should be located at headends of each pool rather than at tailend of pools.
· Emergency siphons or spillways (escapes) must be installed upstream check structure, or in case of drainage water entering canal when demand is low.

Automatic electrical control with undershot or overshot gate.

Same as upstream electrical.

Same as upstream electrical

Hydraulic constant downstream level gates

Same as upstream hydraulic gates.

Same as upstream hydraulic gates

· Sidorejo, Indonesia.
· Massa, Morocco
· Retail office du Niger, Mali
· Tranquillity ID, California, USA
· Victoria, Australia
· Bas Rhone-Languedo, France.

4. UPSTREAM & DOWNSTREAM COMBINED CONTROL

· Automatic upstream and downstream control hardware.
· A buffer reservoir must exist in main canal at point where upstream control shifts to downstream control.

· First gate, at inlet to upper main canal, is used for flow rate control into system.
· All other gates in system only provide water-level control.
· Buffer reservoir stores or releases incremental volume differences between anticipated system demand and actual demand.
· Inlets to secondary canals can be operated with a very high degree of arranged flexibility as all discrepancies will be absorbed in buffer reservoir.

Less expensive than a complete downstream-control system, yet with about same simplicity and advantages.

· System must be operated on an arranged basis (more) restrictive schedules flow into the top of canal is based upon approximate anticipated demands.
· Requires a large buffer reservoir in the system (enough for 1-2 days of operational volume discrepancy between orders and actual deliveries).

· Ideal for a canal with an initial steep slope that ends on flatter topography.
· Buffer reservoir should be located to side of main canal rather than having full canal flow pass into it (for example, to reduce sedimentation).
· Flow-rate changes into canal inlet are based upon daily changes in orders, plus observations of buffer reservoir storage.

· Use modeling to predict wave travel time from inlet to buffer reservoir.
· Make 2 to 3 changes in canal inlet flow rate per day (based upon buffer reservoir water level), rather than only once per day.

· Friant-Kern, California, USA
· Doukkala Sidi-Bennour, Morocco.

5. CENTRALIZED CONTROL

- with non-responsive scheduling

Often manually upstream controlled gates.

Operators are told by central control how to operate gates for each day’s needs, which are generally predicted by some model in central office.

· Central office does not need to listen to field.

· Rarely if ever works as intended, because the control is “open-looped” without any feedback; design and operation assumptions are usually incorrect. In order to even partially of hydraulic parameters work, extensive field calibration of hydraulic parameters must be done.

This is not really a control technology but rather a method of management. It is frequently proposed, however, in recent literature as a means of control.

NE Irrigation Thailand Upper Pampanga, Aurora-Penaranda,
Philippines

- with arranged delivery

· Electrically controlled automates gates
· Micro-processors at each gate
· All gates are electrically moved from a remote centralized control center
· Turnouts are generally not automated, nor are they remotely controlled

· All gates respond to commands from a centralized control center.
· Gates may maintain water levels or pool volumes.
· Central office may use some transfer functions and prediction techniques to send water down canal in anticipation of orders.

· Allows fast response throughout system in case of an emergency, all gates can be shut down quickly.
· Response time in some system is theoretically the wave travel time across one pool rather than along whole canal length, as gates can be moved simultaneously.

· These methods generally require 1-2 day’s advance notice of any turnout flow-rare change responsive.
· Flows are generally input into a simulation program that estimates proper gate settings. Those gate settings are often changed manually from the remote, centralized location.
· Requires extremely dedicated, well-trained. And well-funded staff, maintenance program, communications system, and equipment and sensors.
· Generally these techniques do not maintain constant water levels in pools.

· Suitable for very large canals and primarily for conveyance.
· Especially valuable for areas prone to earthquakes and flooding where quick shutdown of canals is important.

Use same hardware and communications system, but modify the control logic to utilize dynamic regulation (explained below).

· California Aqueduct, USA
· Central Arizona Project, USA

6. RESPONSIVE SYSTEM FOR SLOPING CANALS

· Electrically controlled, automated gates
Micro-processors at each gate
· Some methods have independently controlled gates; others are moved together.
All these systems need centralized monitoring.

· Responds to computer instructions.
· Some maintain water levels; others maintain pool volumes.

· Similar in function to downstream control on level tops. System will automatically provide water to downstream pool as needed, without human intervention and without knowledge of flow rates.
· Fast and automatic response to flow-rate increase or decreases at the offtakes.
· Minimal human intervention needed for actual operation.
· Canal cross sections can be smaller than for level-top canals.

· High risk if personnel, maintenance, initial equipment quality, power backup, communications are not superb.
· Require a high degree of initial planning and modeling maintenance and operation personnel.

Centralized dynamic regulation methods may be compatible with inline hydroelectric installation operations; independent control methods are not.

Large canal cross sections and buffer reservoirs always make control easier even with sophisticated modeling and control.

- with independent controllers

· Radial gates are generally used.
· Remote monitoring is highly recommended.

· Controls flow rate into a pool in order to maintain a specified water level at some point in that downstream pool (that is, they operate on demand)
· BIVAL maintains level at midpoint; CARDD and EL-FLO maintain level in downstream end of pool

· Small, relatively inexpensive controllers.

· These control methods have not had wide application. Knowledge is still being gained regarding design rules and technique for determining proper control algorithm constants.

· Methods do not appear to work well on steep slopes.
· Since they are still in development, a full history of past research and applications is advised before use.
· They are listed, however, because they appear to be very promising once theory becomes transferable and rules for design and limitations are known.

· Tehema-Colusa, California, USA
· Canal du Sahel, Niger

- with dynamic regulation

· Centralized, computerized control center.
· Radial gates are generally used.

· Controls flow in order to maintain desired water level or pool volume.
· Movement of any single gate is calculated in conjunction with other gate movements.

· Very fast, responsive operation.
· Capable of complex operation, such as integration of pumping stations, reservoirs and hydropower generation along the canals.
· Potentially capable of all advantages of independent controllers and centralized arranged and centralized arranged system combined.

Highly sophisticated equipment.

· Several successful systems are in place.
· Proven technology.

· Canal de Provence, France
· Canal de Haouz, Morocco

7. PRESSURIZED SYSTEM

Closed pipe system

· For main and secondary distribution, pipelines are generally high-pressure pipe.
· Similar to municipal system.

· Highest conveyance efficiency.
· Minimal maintenance if property designed and installed, and low silt levels in water.
· No spill
· Simple operation unless complex pumping is needed.
· Minimal land out of production.
· Easy cross-section.

· May require expensive pumping.
Initial investment generally higher than canals.
· Pressure regulators are necessary at turnouts because pressures may fluctuate hourly because of flow changes from turnouts.

· Automatic screening needed at entrance to prevent inlet blockage and subsequent pipe damage during refilling.
· Adequate pressure relief and air venting designs needed.

· Common problem is to undersize the pipes; systems can be very flexible if pipes are large enough.
· Ideally suited for volumetric deliveries.
· Flow measurements of turnouts are simple if water is screened at pipe inlet.

· Westlands WD, Belridge WD, Wheeler Ridge WD in California, USA
· Nehbana, Tunisia