Abstract:
Many irrigation structures have been designed and constructed in past years. But
different researcher shows that most of design irrigation structures do not perform their
proposed uses, because of different reasons. It has been observed in various researches
that some of the schemes have failed to serve the purpose for which they are designed.
Therefore it is important to deal with cause of failure of this structure. The assessment of
problems of small scale irrigation scheme failure with the main objective to assess the
problems of failure of small scale irrigation scheme in case of SNNP Region, Hadiyya
zone in weira scheme was carried out. Failures of weira irrigation project were assessed
by using primary and secondary data. Primary data were collected through field data
measurement, questionnaires and observation. Secondary data were collected from
metrological data, other official documents and design documents. Some of the problems
attributed to the institutional, social and operational problems are lack of adequate
community participation in planning and designing, absence of WUAs, proper handing
over problem and lack of proper training and absence of proper maintenance, evaluation
and monitoring issues. Moreover, hydrologic failure was evaluated by Soil Conservation
Service (SCS) method. The findings related to hydrologic failure revealed that the peak
flood used for the design of the weir is smaller than the result obtained in this
investigation, for irrigation scheme structure of 50 years recurrent intervals were
118m3/s the calculated value of flood for 50 years 155.75m3/sec. Therefore, the other
major causes for the damage of the irrigation structures and overtopping of the canals
and weir were as the result of the flood that came from catchment areas of the streams.
Hydraulic failures were evaluated by lacey’s formula. Actual value of RL of the upstream
and downstream bottom of scour hole (m), upstream and downstream anticipated scour,
scour depth, manning’s roughness coefficient, discharge in canal and velocity, were
compared with the designed value. The finding of these scheme failure shows that there
was main canal siltation, damage on scouring sluice gate, downstream scouring and
damage on downstream apron.
