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 1/

Irrigation schools  Historically there are four main schools of irrigation technology British Dutch French American

British school  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  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) 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 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. 1/

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 - 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 -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) - 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 - Hydraulic simulation to investigate the impact of different sediment management scenarios on sedimentation rates and water deliveries through canal networks.  Environmental Impact - Is intended to be used for project where environmental impacts are to be identified by non-specialists.  Economic Analysis - 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.

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: