Performance Evaluation of Drainage Systems in the Bontanga Irrigation Scheme in the Guinea Savannah Ecological Zone of Ghana

Waterlogging and high salinity levels have been largely due to poor agricultural drainage management. The productivity of agricultural lands could be greatly increased if agricultural drainage systems are properly monitored. This study was conducted in the Bontanga irrigation scheme in the Guinea Savannah Ecological Zone of Ghana to evaluate the performance of the drainage system using drainage performance indicators. Mapping of the components of the drainage system using GPS coordinates and GIS and installation of six (6) observation wells to account for waterlogging intensity and water-table fluctuations with time was done. Three (3) composite soil samples were taken two (2) times during the cropping season at depths of 0–20, 20–40, and 40–60 cm. Drainage coefficients values were computed using a water-balance approach. The findings indicated that the current drainage network conforms with the components of an agricultural drainage system. Electrical conductivity of the soil in the scheme ranged from 0.025 to $0.039\mathrm{dS}/\mathrm{m}$ before planting and 0.065 to $0.098\mathrm{dS}/\mathrm{m}$ after harvesting. Mean sodium values of the scheme ranged from 5.31% to 6.68% before sowing and 6.53% to 10.98% after harvesting. Waterlogging intensity ranged from 155 to 235.5 cm.days for April and 140–240 cm.days for May. Drainage coefficients were found to range from 5.1 to $5.7\mathrm{mm}{\mathrm{day}}^{-1}$ for April and 6.6 to $7.4\mathrm{mm}{\mathrm{day}}^{-1}$ for May. Scheme managers should collaborate with the Water Users’ Associations to enforce bylaws prohibiting the cultivation in the drains, ensuring every farmer maintains the drains and adhere to good water management strategies.

The study was conducted to investigate the drainage system at the Bontanga irrigation scheme in Ghana. The research looked at the components of the drainage system, salinity levels of the soil, waterlogging situation, sodium levels in the soil, and drainage coefficients of the scheme. The findings on the salinity, sodicity, and waterlogging levels of the soil were within acceptable limits. Worth noting is that, though the salinity and sodicity levels were in acceptable ranges, there has been an increase with time. After computation of the drainage coefficient of the scheme using a water balance approach, it was found to be within the range for rice cultivation. The scheme has the components that should be in an agricultural drainage system. However, there are challenges with regards to the maintenance of the drains by the farmers. To ensure proper management of drainage system in irrigation schemes, management should integrate drainage as a key component of the irrigation system and ensure collaboration with water users association at scheme level.