Animal, Plant & Soil Science Animal, Plant & Soil Science E4-9 Drainage

Interest Approach Ask the students if they have ever seen crops growing in standing water and how the standing water might affect the health of the crops. Have them give examples. Ask if they know how the drainage problem can be corrected.

Objectives 1 Determine the need for drainage and describe the benefits of tile drainage. 2 Examine subsurface drainage techniques and determine the equipment and types of pipe available.

Terms aquifers artesian aquifer chain trencher drain tile drain tile breathers drainage drainage plows drainage system

Terms geotextiles groundwater groundwater flow hardpan infiltration laser level perched water table percolation

Terms rockwheel trencher spring surface water throughflow trencher water table

How is the need for drainage determined, and what are the benefits of tile drainage? I. Drainage is the natural or artificial removal of surface and groundwater from a given area. Drainage is important to agricultural production and to manage water supplies.

How is the need for drainage determined, and what are the benefits of tile drainage? A. Precipitation falls to the oceans and land. Precipitation that falls on land either runoffs to form streams, rivers, and lakes or it soaks into the ground. Water that forms streams, rivers, and lakes is referred to as surface water. Water enters the soil layer in a process known as percolation. The downward movement of water through the soil is called infiltration. Some of this water flows horizontally and is known as throughflow. Water found in the pores, cracks, and openings in soil and rock is groundwater. Groundwater can be a long-term source of natural water. Groundwater slowly returns to the oceans. The horizontal movement of groundwater is groundwater flow.

How is the need for drainage determined, and what are the benefits of tile drainage? 1. Groundwater can be extracted through wells. Some wells tap into large underground reserves of water called aquifers. Aquifers may contain vast amounts of water that have collected over thousands of years in underground gravel, sand, and fractured bedrock. 2. An artesian aquifer is one in which the groundwater is confined. In some cases pressure can cause the water to flow up through wells without pumping.

How is the need for drainage determined, and what are the benefits of tile drainage? 3. At some point the ground becomes saturated with water. The top of this saturation zone is called the water table. It is also defined as the surface where the water pressure is equal to atmospheric pressure. 4. A spring occurs when a water table reaches the soil surface resulting in a natural flow of water. Springs are often associated with perched water tables. 5. A perched water table occurs when groundwater meets an impervious layer above the main water table.

How is the need for drainage determined, and what are the benefits of tile drainage? B. Indications of poorly drained soils include standing water that is slow to drain after rainfall, soil that is slow to dry, and stunted crops. Poor drainage is counterproductive to agricultural production. Many crops grow poorly or not at all in poorly drained soils. Plant roots fail to develop due to lack of oxygen and plant growth is stunted. Poorly drained soils also restrict the use of tractors, implements and other machinery.

How is the need for drainage determined, and what are the benefits of tile drainage? C. There are some reasons or situations that soils need improved drainage for agricultural use. 1. Wetlands converted to agricultural use require drainage. Wetland soils tend to have high organic matter content and are suited for vegetable production. 2. River deltas and coastal regions may have high water tables that require drainage if they are to be used for agricultural purposes.

How is the need for drainage determined, and what are the benefits of tile drainage? 3. Regions that receive heavy precipitation that cause the soil to become waterlogged require drainage. 4. Clay soils that drain slowly may require drainage. 5. Soils with an impervious layer of mineralized soil, known as a hardpan, drain poorly. Relatively shallow soils over impervious bedrock also may drain poorly. These situations may call for additional drainage. 6. Irrigated fields in drier climates may require drainage to prevent a build up of soluble salts.

What are subsurface drainage techniques and the equipment and types of pipe available? II. A drainage system can alleviate problems of surplus water. A drainage system is a network of channels, ditches, and drain tile that provide drainage for a field. By removing excess water from the soil, air exchange is improved and thus, growing conditions. Frequently a combination of surface and subsurface drainage will produce the best results.

What are subsurface drainage techniques and the equipment and types of pipe available? A. Surface water can be drained by the contours of the land, ditches, and by pumping. A surface drainage system is effective in draining land with tight soils and steep topography.

What are subsurface drainage techniques and the equipment and types of pipe available? B. The best solution for the removal of groundwater from soil with good hydraulic conductivity is through subsurface drainage. The most common method involves a system of drain tiles. Drain tile is installed below the surface of the soil in order to collect and remove sub-surface water.

What are subsurface drainage techniques and the equipment and types of pipe available? 1. Drain tile may consist of plastic pipe with drain holes or short lengths of burned clay or concrete pipes laid end to end. However, plastic pipe is the most common drain tile material used today. 2. Another option involves the use of gravel and geotextiles. Geotextiles are permeable fabrics that prevent silt or other soil particles from clogging a drain. In this system a trench is dug, lined with a geotextile, filled with grave, folded over the gravel, and covered with soil.

What are subsurface drainage techniques and the equipment and types of pipe available? C. Installation of a drainage system begins with a plan. An engineer may be called on to design a complex system of interconnected drains. 1. Drain tile can be installed in random patterns, parallel, or herringbone patterns based on the topography and water to be removed. Random systems have been traditionally used in poorly drained spots in the fields. The herringbone pattern works well in narrow depressions. Parallel systems have been used to increase productivity on flat, regularly shaped fields.

What are subsurface drainage techniques and the equipment and types of pipe available? 2. The drains are positioned on an angle so water will drain naturally by the force of gravity. A laser level is often employed to ensure an accurate drop in tile elevation. 3. Drain tile breathers or relief pipe are small diameter pipes placed vertically at junctions where the grade of the buried tile changes. The purpose of drain tile breathers is to prevent vacuums from developing as water drains.

What are subsurface drainage techniques and the equipment and types of pipe available? D. Trenches are dug in which to place the tile. Bucket- type excavators may be used for this purpose. However, a trencher is commonly used for digging trenches. Two common types of trenchers are chain trenchers and rockwheel trenchers. 1. A chain trencher looks like a giant chainsaw. It has a digging chain that digs as it rotates around a boom. The depth of the trench can be controlled by adjusting the angle of the boom. The machine creeps backward as the trench is cut. A chain trencher can cut ground and can dig through soil too hard to cut with a bucket- type excavator.

What are subsurface drainage techniques and the equipment and types of pipe available? 2. A rockwheel trencher uses a toothed metal wheel that looks like a giant circular saw. As the wheel rotates it digs a trench. Rockwheel trenchers can cut harder ground than a chain trencher. 3. Drainage plows can be pulled by farm tractors. As they cut into the soil they insert plastic drain tile.

REVIEW 1. How is the need for drainage determined, and what are the benefits of tile drainage? 2. What are subsurface drainage techniques and the equipment and types of pipe available?