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Development of Technical and Financial Norms and Standards for Drainage of Irrigated Lands

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Development of Technical and Financial Norms and Standards for Drainage of Irrigated Lands DEVELOPMENT OF TECHNICAL AND FINANCIAL NORMS AND STANDARDS FOR DRAINAGE OF IRRIGATED LANDS Volume 2 Supporting information relating to the updating of technical standards and economic feasibility of drainage projects in South Africa Report to the WATER RESEARCH COMMISSION By AGRICULTURAL RESEARCH COUNCIL Institute for Agricultural Engineering Private Bag X519, Silverton, 0127 Mr FB Reinders1, Dr H Oosthuizen2, Dr A Senzanje3, Prof JC Smithers3, Mr RJ van der Merwe1, Ms I van der Stoep4, Prof L van Rensburg5 1ARC-Institute for Agricultural Engineering 2OABS Development 3University of KwaZulu-Natal; 4Bioresources Consulting 5University of the Free State WRC Report No. 2026/2/15 ISBN 978-1-4312-0760-2 January 2016 Obtainable from: Water Research Commission Private Bag X03 Gezina, 0031 South Africa [email protected] or download from www.wrc.org.za This report forms part of a series of three reports. The reports are: Volume 1: Research Report. Volume 2: Supporting Information Relating to the Updating of Technical Standards and Economic Feasibility of Drainage Projects in South Africa. Volume 3: Guidance for the Implementation of Surface and Sub-surface Drainage Projects in South Africa DISCLAIMER This report has been reviewed by the Water Research Commission (WRC) and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the WRC, nor does mention of trade names or commercial products constitute endorsement or recommendation for use. © Water Research Commission EXECUTIVE SUMMARY This report concludes the directed Water Research Commission (WRC) Project “Development of technical and financial norms and standards for drainage of irrigated lands”, which was undertaken during the period April 2010 to March 2015. The main objective of the Project was to develop technical and financial norms and standards for the drainage of irrigated lands in Southern Africa that resulted in a report and manual for the design, installation, operation and maintenance of drainage systems. BACKGROUND In South Africa an area of 1 399 221 ha was irrigated and 1 675 822 ha registered for irrigation during 2008 (Van der Stoep & Tycote 2014). It is estimated that 241 630 ha (Scotney et al. 1995) is affected by rising water tables and salinisation and problems appear to be expanding. There are many causes of drainage problems in South Africa. Some typical causes of drainage problems are: • inefficient and badly managed irrigation systems, specifically in the case of very shallow soils and insufficient natural drainage. Salts then start to accumulate and the end result is that the land has to be withdrawn from production, • leaking earthen dams and irrigation furrows, • in some areas terraces are designed and established in order to obtain the right slopes for flood irrigation but, unfortunately, sooner or later drainage problems start to occur at the bottom of these terraces, and • where natural waterways are being cultivated, wet conditions are expected and therefore drainage problems. The main centres where there are drainage problems in the country include: • the areas along the Orange River, especially at Vaalharts, Douglas and Upington, • winter rainfall area at Robertson, Worcester, Swellendam, Ceres and Wellington with undulating topography, • KwaZulu-Natal Region – Pongola and Nkwalini in the sugar producing areas with very heavy clay soils, • Eastern Cape – Gamtoos valley, Sundays River valley and Great Fish River valley, • Mpumalanga, Limpopo and North West region – Loskop and Hartbeespoort Irrigation schemes, and • mainly where there is irrigated agriculture. Planning and design of sub-surface drains was undertaken up to 1965 by members of the Soil and Irrigation Institute, and the staff of the Directorate of Agricultural Engineering. Various approaches were tested and at present designs are carried out according to i selected norms and formulas like the Borehole Method of “Van Beers” to determine the hydraulic permeability, the drain spacing formula of Hooghoudt, and the use of derived formulas from Manning for determining the pipe diameter. Various techniques are currently used to assist the engineering practitioners in the field to quickly determine the layout spacing, pipe diameter, drain slope, etc., from various inputs. Good practices, approaches and design techniques do exist in soil conservation (surface drainage) and need to be revisited, upgraded and compiled in a comprehensive format. With the extensive research internationally and locally, practical experience and testing of drainage techniques and materials by personnel of the Soil and Irrigation Research Institute, the Directorate of Agricultural Engineering and others, a sound foundation of knowledge has been established 25 years ago and the need to update knowledge in this regard is essential. RATIONALE The extent and severity of drainage problems in South Africa is estimated at 241 630 ha (Scotney et al. 1995) and the problem of rising water tables and salinisation appear to be expanding. There are indications that the costs of drainage installation have increase quite significantly. Apart from isolated projects for specific reasons, there has been no comprehensive research on drainage in South Africa over the past 25 years. The existing drainage design, installation and maintenance norms and standards have been adjusted by means of ad hoc studies. Consequently there is a need to revise and publish up to date norms and standards for South Africa. The timing of these revisions is critical because there are only a handful of experts in the drainage field and there is an urgent need to train new practitioners. By extension, it is then expected that these revised standards should form the basis for training of students at tertiary level and guiding of practitioners. The demand for the design of drainage in the field by far exceeds the available capacity. Research output and modelling approaches available internationally should be assessed for applicability in South Africa. Also new ways of managing drainage should be introduced instead of only a narrow focus on the current available solutions. Due to poor quality water, more water for leaching is required which increases the need for drainage under field condition. Leaching is required because yields are declining and economic returns are negatively affected. Old drainage systems are no longer functional or coping because of a lack of operation and maintenance. Unfortunately new drainage systems have not been introduced to cope with the excessive water. The technical lifespan of existing drainage systems has expired, and with new technology the systematic replacement of current drainage systems needs to take place. ii It is essential (actually imperative) to assess the financial feasibility of replacing and installing new drainage systems and this requires decision making support. For existing and new schemes surface runoff has to be realigned and aligned effectively with sub-surface drainage. In the case of revitalisation of irrigation schemes a big component of the funding is allocated to surface and sub-surface drainage. There is a need to justify financial incentives or grants and determine the financial feasibility of drainage at farm and scheme level. Reclamation of irrigation land through drainage will improve production on existing schemes and this will decrease the pressure or need to develop new areas. Effective management of the operation and maintenance of drainage systems will increase water use efficiency and lead to water savings which will support food security in rural areas. OBJECTIVES AND AIMS Main Objective: To develop technical and financial standards and guidelines for assessment of the feasibility of surface and sub-surface drainage systems under South African conditions. Specific Aims: 1. To review internationally and nationally available norms and standards and to give an overview of current drainage systems, practices and technology; 2. To evaluate the interaction between irrigation, drainage practices and impact on the natural environment; 3. To describe technical/physical/biological/financial requirements for drainage; 4. To refine and develop technical standards for drainage with reference to soil types, crops, irrigation method, water tables, salinisation, water quality and management practices; 5. To refine and develop financial standards for drainage with reference to capital investment, financing methods, operation and maintenance expenditure and management practices; 6. To evaluate the technical and financial feasibility of drainage based on selected case studies; 7. To develop guidelines for design, installation, operation and maintenance of drainage systems. METHOD The research method followed in the research project was tailored to answer the specific aims. The specific method followed for the specific aims are summarised as follows: iii Aims 1, 2 and 3 Literature reviews of local and international books, journal articles and internet publications were conducted, and from these sources the terminology, definitions, practices and technology of the various drainage approaches were identified and documented. The descriptions included engineering, soil science, environmental and economic approaches on drainage. The review of literature also provided an overview of current drainage systems, practices and technologies worldwide, and those suited to South African conditions. Appropriate research study sites were identified based on available
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