THE EYE ON ATLANTIS: FLOOD MONITORING
Radar estimation of rainfall is widely used and is not strictly “emerging”. Radar provides an aerial indication of rainfall, and so provides a better distributed measurement than from point rain gauge measurements, with the output lending itself well to use in grid based models. There are a number of limitations in measurement accuracy such as range, attenuation of
signal and calibration, but second-generation radar instruments, particularly Doppler radars, have overcome some of the attenuation problems. Smaller radar instruments (C and X-band radars), sometimes portable, are useful for local monitoring, especially in urban areas. The combination of radar with NWP used in short lead time forecasting models has resulted in a
considerable scientific advance, allowing prediction of cell development and decay as well as trajectory. There are two other persistent problems relating to radar, the first being cost and the second being the means of transferring radar information from purely visual to digital inputs.
Currently 28 space agencies along with 20 other national and international organizations participate in CEOS (Committee on Earth Observation Satellites) planning and activities. The NASA satellite monitoring programme produces both real-time and research-merged 3-hour global precipitation products available on an ftp server for public access. However, this service requires considerable resources to support ground validation sites and research. The capabilities of geo-stationary satellite systems have improved steadily, providing more rapid updating (time scales shorter than 30 minutes) and increasing spatial resolution. Rainfall estimation from geostationary satellite platforms uses infra-red (IR) sensing based on the relationship between cloud-top growth and surface precipitation, and is best for convective rainfall.
PREVENTION AND MITIGATION OF FLOODING
Floods prevention and mitigation involves the management and control of flood water movement such; as reducing flood runoff through the use of flood walls and flood gates. It also involves the management of people through measures such as excavation and dry/wet proofing properties.
It can be studied in three levels
- Creation of a flood risk map and emergency communication plans. Flood risk maps would stipulate areas which are unsafe for habitation hence reducing the amount of property and life that would be lost to flooding. Emergency communication plans would warn the population in the floodplain in time to reduce the loss of life.
- Individual properties; property owners may fit their homes to stop water from entering the house. Personal flood plans may involve blocking doors and air vents, water proofing important areas and sandbagging the edges of the building.
- Protection of communities; when more homes, shops and infrastructures are threatened by the effects of flooding, rivers running through large urban developments are often controlled and channeled. This defense can be done by raising the edge of the water with levees, embankments or walls.
METHODS OF FLOOD PREVENTION
- Sea/coastal defense walls: Sea walls and tide gates have been built in some places to prevent tidal waves from pushing the waters up a shore. In some areas sandbags are made and placed in strategic areas to retain flood waters
- Retaining walls: Retaining walls, levees, lakes, dams, reservoirs or retention ponds having been constructed to hold extra water during times of flooding.
- Town planning: it is important for builders to acquire permission before buildings are erected. This will ensure that water ways are not blocked. Also drainage systems most be covered and kept free from objects that may choke them. This way water can easily run through if it rains and minimize any chance of town flooding. Drainage systems should be covered to prevent litter from getting into them.
- Education: in many developing countries drainage systems are choked with litter and people having little knowledge of the effects that it can have during a rain. When it rains finds its way into streets and into people’s homes. Educating people on this aspect will reduce the probability of floods occurring hence saving property and lives.
- Detention basin: small reservoirs built and connected to water ways. They provide temporary storage or flood waters. This means in an event of flooding water is drained into the basin first giving people more time to evacuate. It can also reduce the magnitude of down slope flooding.
- Vegetation: trees, shrubs and grass help to protect the land from erosion by moving water. People in low lying areas must be encouraged to use a lot of vegetation to help the power of moving flood water and also help to reduce erosion.
- Avoid living in flood prone areas.
- Building artificial levees along the banks or fivers by filling of bags with gravels along flooded areas.