This report intends to contribute to the upgrading of the hydraulic infrastructive in existing lowland schemes, where water quality (acidity) problems occur. A summary of the contents of this report is given below: Chapter II presents an overview of the already implemented lowland schemes in Indonesia and describes some alternatives for lmproving the Baramai-Seluang-Belawang-Muhur unit. Chapter VII covers a cost-benefit analysis for this intepretation. These data concern hydrometry, geometry and acidity. Chapter IV discusses the set up of an unsteady flow model, which is based on the PENPAS programme. This is foliowed by the scherr.atization of the study area, (defining nodes, branches, boundary conditi.ons and init ia l conditions), the calibrations and the verification of the rnodels, based on field data. This chapter is co mple t ed by the presentation of the results and an analysis of the alternatives. Chapter V covers the interpretation of the results. Furthermore each alternative is discussed. From the computational results it can be concluded that the convective transport in the system is very dominant. By introducing the flushing canal without any regulatin g structure, it can create only very limited net outflow for each of the secondaries. It does nat give signif.icant d.ifferences between the system without flushing canal and with flushing canal (bath with improved tertiary canals) or with interupted flushing canal. So, in order to have a better flushing effect, a system with a larger net outflow (wider secondary caoals or with a regulating structure) is needed. This idea (wider secondary canals) can be applied for the secondary left of Barambai and the secondary of Seluang. For the wet season condition it wil! give an improved circulation in the system, but unfortunately for the dry season condition, a deadlock problem will occur in two of the secondary canals (the Barambai right and Muhur). So, in these canals sedimentation may occur besides poor refreshment of the canal water. To avoid this problem, a regulating structure must be introduced for example at the end of those secondary canals. Then an optimalization study must be carried out in order to have an optima! salution for a water management strategy. Chapter VI discusses erosion and sedimentation problems in the canal system, by means of sourees of sediments and proteetion works against the local scouring. Chapter VII covers a cost benefit analysis for this upgrading work based on the internal rate o f retu rn of 15%. (RUN 04). Chapter VIII contains the conclusions and recommendations for impravement of the water mana ge ment system of the Barambai-Seluang-Belawang-Muhur unit in particular, and for new lowland development and other upgrading actlvities in general. References are given after chapter VIII. Annex 1 briefly describes the theoretica! background of long waves and the formulae used for calculation of transport of dissolved matter. Annex 2 describes the PENPAS computer program and its facilities. Annex 3 describes about Hydraulic Levelling in Swampy Areas which was also presented during the Third Congress of the Asian and Pacific Regional Devision (APD) of the IAHR (August 1982, Bandung, Indonesia). Annex 4 gives examples of the input and output files of the alternative Run04. Annex 5 presents Hjulstrom's graph related to theerosion and deposition of the particles.