Planning exhaust duct should provide a cost breakdown of the execution and maintenance of the minimum. Segments of the channel should be stable against erosion and sedimentation should be minimal at every cross-section and must be balanced. With the waster water from rice fields to be cleaner than the sediment. Erosion in the discharge channel will be the decisive criterion.
Free flow of the plan should not exceed the maximum allowable speed.
Maximum permitted speed depending on soil type and condition. Waster channel designed in the lowest and through the depressed areas. The natural slope of the land determines the slope of the discharge channel extends. When the bottom slope is too steep and maxi-mum speed will be exceeded, it must be made of the building falls. Free plan should be taken at or near the maximum allowable speed, because the discharge plan or peak discharge is not often the case, the discharge and velocity of water flow in the discharge channel will be lower under average conditions.
If the discharge flow is low, the flow will tend to be meandering when the basic channel width. Therefore typically designed relatively narrow discharge channel and in comparison to the irrigation channel. Variations in water level at the rate that varies, usually does not have significance in other discharge channel. The cross-section will provide a more economical solution. In planning for land drainage system there are some data that must be provided, namely, (1) a description of the physical environment of the drainage system, (2) land use, (3) other infrastructure, (4) topography, (5) the natural flow patterns.
A. Description of the Physical Environment Drainage Systems
In planning the layout of the drainage network. description of the physical environment is a very important information. Channel placement. density of buildings and the number of such facilities will be strongly influenced by the condition of the region will be affected oieh conditions of the plan area. In this regard, a planner is required to always be sensitive in interpreting the data provided in the form of secondary data such as base maps and flood phenomena that have occurred, as well as the existing natural flow patterns. Where information about the natural flow patterns can also be obtained and direct observation in the field when it rains (floods).
B. Land Use
A land use map which can describe the pattern of the lawyer-use of land area drainage plan. The pattern of land use in question should include on existing conditions as well as plans for future development. The information is needed to determine the scope of the necessary drainage system and to plan drainage level according to the category of land use of the area.
C. Other infrastructure
Information about the other infrastructure shall include road networks and other networks which are expected to cause a disruption in the drainage system. It is intended as a consideration in determining the height of the drainage channels and to identify the type of building which required investigation.
D. Topography
The information required to determine the direction of drainage channels and boundaries penanmpungnya. Mapping the contours on a farm needs to be done on a scale of 1: 5000 or 1: 10,000 with different contours on a flat area of 0.5 meters, and 1.0 meters depending on the contours of the steep terrain. Mapping the need to refer to a bench mark in the field known.