【正文】 of the city, New Orleans lies in a bowl with the downtown area under about 3 m below mean sea level. () the storm surge created by hurricane can threaten the city from the sea and from the tidal Lake Pontchartrain to the north. During Mississippi floods the river itself threatens the city. The entire urbanized area is surrounded with levees, floodwalls and steel gates (to be closed above a critical level).Once the city is inundated, the water has to be pumped to drain from the lowlands. Long time immerging duration will make the infrastructures and property damaged more seriously. The flood water caused by hurricane Katrina cost 6 months to be pumped out pletely. Rapid land subsidence in recent years makes flood protection situation worse. The recent topographic survey to the elevation of the land surface in New Orleans indicates“Considering the rate of subsidence and sea level rise, the area of New Orleans and vicinity that are presently to 3 m below mean sea level will likely be to m or more below mean sea level by 2100.” The sinking land surface threatens New Orleans’ infrastructure and handicaps the city’s ability to survive the lake and gulf surges of powerful hurricane. Topography of New Orleans4 Coastal erosion During the 20th century, coastal Louisiana has lost over 4800 km2, an area more than 25 times larger than Washington, . During the decade of 1990 to 2000, land loss approximately 66 km2 per year that is an entire football field every half hour, largely through conversion of vital coastal wetlands to open water (about 25% of wetlands lost in last 50 years). This loss accounted for an estimated 80% of the coastal wetland loss in the entire continental United States during 1990s. The Louisiana shoreline will advance inland as much as 52 km in some areas because of land loss. Scientists estimate that if recent loss rates continue into the future, even taking into account current restoration efforts, then by 2050 coastal Louisiana is expected to lose more than 1800 km2 of coastal marshes, swamps, and islands. The loss could be greater, especially if worstcase scenario projections of sealevel rise are realized, but in some places there is nothing left to lose.Many studies have been conducted to identify the major contributing factors and agreed that land loss and the degradation of the coastal ecosystem are the result of the cumulative effects of human and natural activities in the coastal area which severely impaired the deltaic processes and shifted the coastal area from a condition of net land building to one of net land loss.l Decrease of freshwater and sediment delivered from Mississippi River. In the last century, the levees and associated navigational works of the Mississippi River prevent the overflow of fresh water and sediments into the adjacent marshes during spring floods. These structures extend to the river39。 2) the efforts from single sector can not address flood problem and coastal erosion. people started to reconsider hurricane protection plan bining with coastal restoration from sustainable, longterm and prehensive vision. Excepting existing programmes like the Coastal Wetlands Planning, Protection, and Restoration Act (CWPPRA)。 the Coastal Impact Assistance Program (CIAP)。 and the US Army Corps of Engineers (USACE) Louisiana Coastal Protection and Restoration (LACPR) Study, some international exchanging projects are ongoing, which are providing the experience and lessons about flood management in coastal areas between countries. For flood management in Mississippi River Delta, broader and more intensive partnership are promoted and required, determining the success of any integrated management in the flood control related sector. It is obvious that no single sector can be expected to shoulder the management burden alone, and that far more integrative strategies need to be devised for each new project that is undertaken. “Multiple lines of defense” strategy for hurricane protectionBarrier islands, healthy marshes, natural ridges adjacent to bayous, and cypress swamps provide a natural buffer during storms by slowing down and reducing ining surges of water. This function, bined with manmade levees and other flood control measures, has allowed Louisiana’s working coast to exist in a floodprone area.l The concept of natural lines of storm surge defense is based on the hydraulic principle that surge elevation is effectively reduced by the friction of flowing over a vegetated land mash. l Historically an engineering “rule of thumb” has been used for estimating potential storm surge reduction in coastal Louisiana. The engineering “rule of thumb” for the effect of coastal wetlands in reducing storm surge elevation provides for an estimated of surge reduction for each 6km of wetlands over which the surge must flow. Innovative flood control structuresAs hurricane protection options are considered for the coast, a balance must be struck between two urgent needs. On one hand, residents need storm protection. These munities could not exist without levees. In recognition of the need for structural protection, levees are remended in high risk areas that must be protected if we are to avoid severe consequences for the state and nation.On the other hand, there is legitimate concern that building levees across wetlands can stop the natural flow of water, creating impoundments that flood munities and lead to further land loss. Finding the right mix of options requires that innovative technologies to build modern flood control systems. It bears little similarity to the traditional earthen levee embankments that have historically dominated Louisiana’s flood control plans. Levees must be built with innovative designs, since we now recognize the importance of tidal exchange and natural hydrology in sustaining wetland ecosystems. If a levee is deemed appropriate for an estuarine basin, we must do the following things: