Summary of Gronddreineringstelsels en Beplanning

## Introduction Soil drainage systems remove excess groundwater from agricultural land so crops can grow well. High water tables make soil wet, reduce aeration in the root zone, cause salt buildup and can drown plants that are not adapted to wet conditions. Proper drainage improves crop health and farm productivity. > **Definition:** Soil drainage is the controlled removal of excess water from soil to maintain suitable moisture and aeration for plant growth. ## Why drain soil? - High water table = wet soil = poor crop growth - Poor aeration in the root zone reduces root activity and nutrient uptake - Salts (brackish salts) can accumulate when water does not drain - Low-lying areas or land near rivers often have naturally high water tables - Leaking irrigation canals and dams can raise the groundwater level in intensive farming areas ## Factors that determine the drainage system - **Soil texture and class:** sand, clay, or mixed soils affect how water moves - **Depth of the groundwater table:** determines how deep pipes should be placed - **Impermeable layers:** clay layers, limestone, or rock limit downward movement of water and influence design After investigating the above you can decide: 1. Which **crops** to grow 2. Which **irrigation method** to use 3. Which **drainage system** to implement ## Types of drainage systems ### Open drains (ditches) - Laid out following the land contour - Advantages: quick to construct, low cost - Problems: weeds and pests breed in ditches, restrict tractor movement, and soil loss from edges ### Pipe drainage systems Pipes collect and carry water away from the field. - **Earthen (unglazed clay) pipes**: diameter $75$–$200\,\text{mm}$, segments usually $3\,\text{m}$ long; water enters through openings between segments - **PVC pipes (polyvinyl chloride)**: diameter $50$–$150\,\text{mm}$, lengths about $6\,\text{m}$; have narrow slots in the walls to prevent fine sand and roots entering > **Definition:** PVC is polyvinyl chloride, a common plastic used for drainage pipes because it is smooth, durable and comes in long lengths. ## Design considerations for pipe drainage - **Spacing of drains** depends on: soil texture and depth of impermeable layers - Coarser soils (sandy) allow wider spacing; finer soils (clayey) need closer spacing - **Correct pipe sizing:** too large increases cost; main lines must be large enough to carry flow from lateral lines - **Minimum slope (fall):** at least $0.2\%$, which is a fall of $20\,\text{mm}$ per $10\,\text{m}$ length > **Example:** For a $100\,\text{m}$ lateral with $0.2\%$ fall, the total drop required is $0.2\%\times 100\,\text{m} = 0.2\,\text{m} = 200\,\text{mm}$. ## Planning the drainage layout - Draw a sketch of drainage lines so blocked pipes can be located and repaired easily - Choose a drainage pattern based on land shape: 1. Natural system: follow existing wet patches and natural drainage paths 2. Herringbone (fishbone) system: used where land forms a valley; laterals feed into a central collector 3. Grid (or lattice) system: used on flat land with a gentle slope to one side ## Safety and maintenance precautions - Install service (inspection) pits at regular intervals along the drainage system - Service pits must be large enough for a person and have a strong cover to prevent falls - Protect pipe outlets with wire mesh to stop mice and rodents entering and nesting, which can block pipes > **Definition:** Service pit (inspection pit) — an access chamber that allows inspection, cleaning and maintenance of drainage pipes. ## Comparison table: Open drains vs Pipe drains | Feature | Open drains (ditches) | Pipe drains | |---|---:|---| | Cost | Low | Moderate to high | | Installation speed | Fast | Slower, needs planning | | Weed/pest problem | High | Low | | Loss of soil | Yes | Minimal | | Machinery access | Restricted | Unaffected |