Your Result:

There are many challenges and limitations associated with the hydrological analysis of spate river systems. Which of the following would you regard as the most significant?

	a) Rainfall and run-off processes in the catchments of spate-irrigated areas that are mostly located in arid and semi-arid areas are subject to a much larger variability between and within years than in perennial river systems. Long-term data records are needed, but measured data is usually either very sparse or nonexistent in spate-irrigated areas. Hydrological analysis thus cannot usually be based on existing long-term rainfall and run-off records.
	b) Most of the run-off occurs during short spate events. Spate flood hydrographs usually have a very rapid rising limb followed by a longer recession. This is quite different to a triangular hydrograph assumed in some standard rainfall run-off models.
	c) Spate floods are usually generated by intense rainfall occurring only over a part, in large catchments possibly only a small part, of a catchment area. Some storms may only be partly represented or even completely missed by the sparse rain gauge networks found in many catchments.

CORRECT ANSWER:
a) Rainfall and run-off processes in the catchments of spate-irrigated areas that are mostly located in arid and semi-arid areas are subject to a much larger variability between and within years than in perennial river systems. Long-term data records are needed, but measured data is usually either very sparse or nonexistent in spate-irrigated areas. Hydrological analysis thus cannot usually be based on existing long-term rainfall and run-off records.

Measured data is usually sparse or nonexistent in spate-irrigated areas. In this situation, which of the methods listed below describes the best approach for deriving hydrological information needed to support the design of intakes, water distribution and cropping systems?

	a) Application of rainfall/run-off modelling.
	b) Monitoring programmes to quantify catchment rainfall and run-off at proposed diversion sites.
	c) Application of local/regional empirical relationships that predict annual run-off and flood magnitudes from catchment characteristics and rainfall.
	d) Use local knowledge of the timing, numbers and sizes of floods in different years, supplemented by water level/discharge calculations, to develop estimates for expected flood discharges and volumes available for irrigation. When existing schemes are to be improved, determine existing irrigated areas and interview farmers to establish how often fields in different parts of the system are irrigated, and how this varies between years. (The hydrology is on the ground!).

CORRECT ANSWER:
d) Use local knowledge of the timing, numbers and sizes of floods in different years, supplemented by water level/discharge calculations, to develop estimates for expected flood discharges and volumes available for irrigation. When existing schemes are to be improved, determine existing irrigated areas and interview farmers to establish how often fields in different parts of the system are irrigated, and how this varies between years. (The hydrology is on the ground!)..

Weirs are used at diversion sites to raise and stabilize command levels. What is the morphological impact of weirs located in steep channels carrying high sediment loads?

	a) A raised weir heads up flows facilitating diversion to canals. Some bed scour occurs downstream from the weir.
	b) The pool formed upstream from a weir rapidly fills with sediment, and upstream bed levels rise to the weir crest level. Initially quite severe bed scour occurs downstream from the weir, until the coarse sediment supply is re-established as the upstream bed levels rise.

CORRECT ANSWER:
a) A raised weir heads up flows facilitating diversion to canals. Some bed scour occurs downstream from the weir.

Sedimentation is a major feature in spate irrigation schemes, due to the very high sediment loads transported by spate rivers. Which of the statements below describe the best approach to managing sedimentation?

	a) Prevent high sediment loads from entering an irrigation scheme by excluding or trapping sediments at the river intake.
	b) Spate systems "grow" their own soils. In most areas cropping is only possible because of the deep deposits of fine alluvial sediments that settle on the fields, and an annual supply of nutrients carried with the silt and clay fractions. Ensure that fine sediments diverted from the river are conveyed to the fields.
	c) Fine sediments are needed on the fields while coarse sediments settle and block canals and water control structures. Exclude or remove the coarsest sediment fractions at intakes, and design canals to ensure that fine sediments are transported through to the fields.

CORRECT ANSWER:
c) Fine sediments are needed on the fields while coarse sediments settle and block canals and water control structures. Exclude or remove the coarsest sediment fractions at intakes, and design canals to ensure that fine sediments are transported through to the fields.

What is the most effective method of minimizing the entry and deposition of coarse sediments in spate irrigation canals?

	a) Locate an irrigation intake at the outside of a channel bend.
	b) Limit abstractions of very high flood flows, as these carry the highest concentrations of coarse sediments.
	c) Provide a "sediment-excluding" intake.
	d) Remove coarse sediment with a sediment extractor or settling basin.
	e) Make provision for routine canal desilting to maintain canal discharge capacities.

CORRECT ANSWER:
a) Locate an irrigation intake at the outside of a channel bend.