Sanitary Engineering Lecture 11

Storm Water Runoff Storm water runoff is the precipitation which seeps into the ground if precipitation occurs faster than it can infiltrate into the ground. Runoff remains on the surface and flows into streams, rivers, and eventually large bodies such as lakes or the ocean. Infiltrated groundwater moves similarly as it recharges rivers and heads towards large bodies of water. So the runoff of water is divided into upper and lowers the ground surface.

Upper the Ground Surface Runoff: Storm water upper the ground surface is collecting or harvesting. Collecting storm water for storage or recharging the underground aquifer. Water harvesting is the process of intercepting storm water runoff from a surface (e.g. roof, parking area, land surface), and putting it to beneficial use. Intercepted storm water can be collected, slowed down, and retained or routed through the site landscape using micro basins, swales and other water harvesting structures.

Capturing and using storm water runoff also reduces site discharge and erosion, and the potential transport of storm water pollutants. The water harvesting is not cost more because the site development costs typically include design, grading, and landscaping. Long-term maintenance adds to these initial costs. There are many ways and techniques to collecting the upper runoff, every way or technique has special characters and use. Some of these techniques are:

Roof top harvesting: Roof top harvesting is an old technique and use since today it's practiced in many places throughout the world, the rain water can be diverted to the existing wells or tanks as well as use at the west bank.

Streets as harvesting facilities: The simplest and most obvious facility for harvesting of site runoff is the use of streets and roads as channels. This technique is become the storm water harvesting system for most of the countries. There are two types of road drainage:  Roof type roads.  Channel type roads.

Open Channel: This technique is more elaborate because they use does not involve flooding the streets also the channel can trap sediment. This technique is used near the high ways at Jordan Micro basin: It is a technique to collect storm water in localized basins served by small watersheds. Micro basins are appropriate for use on gently sloped or nearly flat land with low volumes of runoff water such as along sidewalks, in landscaped areas, in parking lot planters, etc. Micro basins can be used in areas with more concentrated runoff if they are arrayed in a series with spillways in between.

French Drains: French drains are rock-filled trenches that are designed to encourage rapid storm water infiltration through the sides, ends and bottom of the trench where soil and water meet. Because they are filled with rock, French drains hold only about one-third of the water that an open trench would hold. French drains can intercept low to moderate flows depending on their size. French drains are typically used on flat to moderate slopes. French drains should receive runoff water only from watershed areas that are relatively free of sediment like parking lots, rooftops, sidewalks, or areas stabilized with vegetation.

French drains should not be built in a watercourse, where silt could quickly clog the pore spaces. French drains are useful for intercepting water in areas where a level surface is needed. French drains could be used on steeper slopes where water harvesting basins would have only small storage volumes. Reservoirs: This technique is constructed to collect rain fall directly or by allow rain water to flow into the reservoirs. This may be ponds or pits out in open areas with impermeable base and walls such as concrete reservoirs

Gabions: Construct a semi permeable barrier or grade control structure to slow, but not stop, the flow of storm water in a small watercourse to help prevent or repair upstream erosion, trap rich detritus, and allow storm water to infiltrate into the channel sediments and adjacent soils. Also gabions can be used as a barrier or side wall around a reservoir for collecting storm water.

Lower the Ground Surface Runoff: After collecting the storm water from the upper runoff, the water travel to its direction under the ground surface. The lower surface techniques are:  Pipes.  Channels.  Culverts.  Inlets.  Manholes.  Pumping station.