6.10
SHARC Software usage for
Spate irrigation
John Paul van der Ham
Content
 Irrigation schools
 Highlights of Spate Irrigation
 Introduction to SHARC
 Components of SHARC
 SHARC and Spate Irrigation
 DORC – DOSSBAS
 Workshop Engineering
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Irrigation schools
 Historically there are four main schools of
irrigation technology
• British
• Dutch
• French
• American
British school
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From mid 19th century
Sudan, Indian sub continent
Large canals in morphologic unstable soils
Low sediment load
Long canals, proportional
Regime theory developed (empirical, 1930’s Lacey)
NO variation in canal water flow!!
 Productive and protective systems
 Head-tail end problems
Dutch school
 Indonesia, humid tropics
 Flashy floods in short rivers
 Main problem: stability of head works
 regime theory, refined by Vos and Vlugter who
found v times S should be constant or increase in d/s
direction
 Irrigation: water and fertile silt
 Development of the Romijn weir
 Drainage problem incorporated in distribution
structures
French school
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Based on Po-plains traditional technology, further
developed in North Africa (early 20th century)
Clean water (erosion ‘control’ and reservoirs) in
water scarce areas
 check on maximum canal velocities and lining
of canals, detailed distribution according to crop
requirements
Strict water distribution up to farm level
Variation in water flow part of design
Complicated technology
Step-wise distributor, AVIO gates etc
USA (American) School
 Clean water (erosion control and reservoirs)
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in water scarce areas
Reservoir irrigation
Large farms; no tertiary unit
Strict water ownership rules
 Canal design: check on maximum flow
conditions, prevent losses ( lining)
Tractive force theory in canal design (shear
stress depending on slope and water depth)
Distribution methods
 Continuous flow / proportional flow
 Rotational systems (on-off systems)
 On-demand systems
 Protective / Productive irrigation concept.
Highlights of Spate Irrigation
 Spate systems vary in size, layout, structures and
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management.
Management of floods requires direct irrigation.
Combined with heavy sediment loads
Uncertain water availability and unpredictable flood
discharges
Spate irrigation requires a strong organisation and
management to take care of the operation and
maintanance activities including the technical and
financial aspects.
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Introduction SHARC
 SHARC is a suite of integrated programs designed to
assist in the identification and solution of sediment
problems at intakes in rivers and canal systems.
 Developed to assist in design and rehabilitation of
large systems…
 Consists of 6 modules:
-Problem diagnosis and initial options
-Preliminary Economic Screening
-Design Tools (4 design programs)
-Hydraulic Simulation
-Environmental Impact
-Economic Analysis
Components of SHARC
 Problem diagnosis and initial options
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Sediment control structures that are technically feasible can be
identified on the basis of the intake type and the possibility of
hydraulic sediment flushing.
 Preliminary Economic Screening
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The preliminary economic screening module enables preliminary
estimates to be made of the allowable costs for sediment control
structures, that provide a specified Internal Rate of Return (IRR).
> (Savings and or increased irrigated area)
Components of SHARC
 Design Tools (4 design programs)
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The Intake Model can be used to provide an indication of the
impact of modifying an existing conventional intake.
Three programs that are used to design of alluvial canals,
(DORC), sediment extractors (DACSE) and settling basins
(DOSSBAS).
The methods in DORC enable canal designs to be matched to
the expected incoming sediment load through the use of one of
the design philosophies (four schools).
DOSSBAS is a suite of programs, which assists the design of
sluiced or mechanically excavated settling basins. The program
predicts the sediment concentrations and sizes passing a basin.
It can be used to model still pond regulation at an intake.
DACSSE provides a set of methods to aid the design of vortex
tube and tunnel sediment extractors.
Components of SHARC
 Hydraulic Simulation
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Hydraulic simulation to investigate the impact of different
sediment management scenarios on sedimentation rates and
water deliveries through canal networks.
 Environmental Impact
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Is intended to be used for project where environmental impacts
are to be identified by non-specialists.
 Economic Analysis
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Enables a cost-benefit analysis to be undertaken on potential
solutions identified using the other SHARC modules.
SHARC and Spate Irrigation
 Adventage – SHARC gives possibilities to
analyse and determine interventions to deal
with sedimentation issues.
- Gives range of interventions
- Can indicate cost and benefits
 Word of caution – Also SHARC requires
inputs, for spate these are commonly based
on rough estimations since they are hard to
measure and to predict.
DORC – DOSSBAS
 The module Design Tools with DORC and
DOSSBAS require not to many inputs and
can support with canal design and settling
basins.
 2 evening workshops, one for DORC and one
for DOSSBAS.
Recommend formula for spate canal design
no scouring – no silting” criteria – not for spate
“Regime” design methods mostly for canals carrying low
sediment loads but Simons and Albertson method include
equations for canals with sand beds and cohesive banks,
carrying “heavy” sediment loads – have been used in spate
systems
 Rational methods provide the most logical method of designing
canals to achieve a specified sediment transporting capacity.
Chang, 1985 method provides predictions of slopes and bed
widths that are similar to that observed in many spate systems.
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Use canal surveys to aid design in modernised
schemes
 Canal designs in modernised schemes are best
based on the slopes and cross sections of (stable)
existing canals. Design of enlarged, extended or new
canals can then be derived using the Chang
equation, with a judicious choice of input parameters
to provide a good match with the slopes and cross
sections observed in existing canals.
Workshop Engineering
 Using 12 Computers
 Using SHARC software
 Using Software Manual
-Working Through Tutorial 3 (a) to (d)
-Working Through Tutorial 5 (a) to (d)
 Working in couples
After workshop..
 Can always ask support from:
p.lawrence@sediments.plus.com