Flooding in Louisiana

Flooding in Louisiana

Introduction

Louisiana has problems with flooding. The Mississippi River borders the East Side of the state and often floods due to precipitation. Other for reasons flooding includes dam failure or land problems. The flooding has a major affect on the people in the state since they must . deal with the water and all of its damage. The scope of the problem is precipitation. Hurricanes can hit Louisiana and cause flooding in the lower Mississippi. Also heavy rains often hit the state. "A slow moving weather system dropped large amounts of rain over northern Louisiana..."(FEMA, Feb 1, 99). The amount of time in which rain falls is an uncontrollable factor causing the state tobe well prepared for all types of flooding. Dams are a good way to help the flooding. Flooding is an earth science related problem in Louisiana.

Physiographic Province

Louisiana lies in the Mississippi River valley and borders the Gulf of Mexico. The problem flooding areas are those closest to the Mississippi River and the delta. The other states that touch the river are Minnesota, Wisconsin, Iowa, Illinois, Missouri, Tennessee, and Arkansas.

New Orleans is a city that is very vulnerable to flooding because much of

the city is below sea level. The below sea level parts of the city must be keep dry by constantly pumping water into the Mississippi or to the sea, otherwise those areas would flood from groundwater alone. Even the portions of New Orleans that are not below sea level are a part of the vast Mississippi flood plain. Flood plains are places where rivers flood

during normal conditions. Dam-like ridges form along the banks of rivers on flood plains and under normal conditions keep the river in its channel. During floods rivers flow over the tops of levees and flood the flood plains that lie adjacent to the river channel. Man has constructed channel walls to "beef up" the natural levees to protect the flood plains. However, all of New Orleans and the flood plain beyond the city is constantly threatened by flooding of the Mississippi River (Madsi, July 99).

Flooding

A flood is a temporary overflow of a river onto adjacent lands not normally covered by water. Causes for flooding include higher than normal amount of precipitation. Furthermore, cooler than normal temperatures can make the ground cold so there is less evaporation of water (NSC, February 98). Rainstorms are short periods of very heavy rain that fall over a small area. They can cause flash floods, as rivers become torrents (Wood). However that may soon change. The National Weather Service is responsible for predicting the weather and warning people about severe weather. Up until now, meteorologists could only guess when a flash flood would occur. Now, they have a new tool, called Doppler radars, which can track rainfall street by street. This should provide more accurate flash flood warnings across the country. The new radar systems should allow meteorologists to provide warnings before a flash flood occurs (PBS). In any given stream, river, or watershed, annual flood pulses may be common, but large-recurrence intervals, major flood events are rare (Michener).

Precipitation

Exceptional precipitation makes the Mississippi River flood in Louisiana. Usually when combined with several other factors and exceptional precipitation flooding occurs. The coast floods due to hurricanes and high tides. Global warming can also cause the seat to rise on the coast.

Streams

A stream channel is the conduit for water being carried. The volume of water passing any point on a stream is called the discharge. When the discharge becomes to high, the stream widens its channels by overtopping its banks and flooding the low-lying areas surrounding the stream. Straight channels are rare; they are relatively straight in direction. Meandering channels were straight at one time. They migrate back and forth on the flood plain. Braided channels have islands and bars in them.

Deltas and drainage systems

A delta is when a stream enters a standing body of water (Fig 1). They build outward from the coast. Drainage systems develop in such a way as to efficiently move water off the land. Each stream in a drainage system drains a certain area, called a drainage basin.

Figure 1, Delta

In a single drainage basin, all water falling in the basin drains into the same stream. Drainage basins can range in size from a few km2, for small streams, to extremely large areas, such as the Mississippi River drainage basin, which covers about 40% of the contiguous United States. (Fig 2) These are types of drainage patterns (Nelson, March 2000).

Figure 2, Drainage Patterns

Erosion

Streams erode because they have the ability to pick up rock fragments and transport them to a new location. The size of the fragments that can be transported depends on the velocity of the stream and whether the flow is laminar or turbulent. Turbulent flow can keep fragments in suspension longer than laminar flow. Streams can also erode by undercutting their banks resulting in mass-wasting processes like slumps or slides. When the undercut material falls into the stream, the fragments can be transported away by the stream. Streams can cut deeper into their channels if the region is uplifted. As they cut deeper into their channels the stream removes the material that once made up the channel bottom and sides.

Levees

Natural levees are constructed as a result of flooding, but natural levees tend to be relatively low and do not offer much protection from large discharge because they can easily be overtopped. Human made levees, such as those on the Mississippi River, are much higher and are constructed to prevent flooding from high discharges on the River. Most levees are constructed of piles of dirt with a concrete cover on the riverside of the levee. Such levees often give a false sense of security for those living on the flood plain. The levee was built to protect, because failure of such levees can lead to flooding, either because discharge can become great enough to overtop the levees or the levees can become weakened and fail (Nelson, March 2000). The levees are constructed by the federal government and are maintained by local interests, except for government assistance