的 波西米亚溢洪道 is located in Plaquemines Parish on the east bank of the Mississippi River about 35 miles southeast of New Orleans, LA. 在20世纪20年代，密西西比河在新奥尔良的水位越来越高，越来越有威胁, and so the 波西米亚溢洪道 was authorized in 1924 by the Louisiana State legislature for the purpose of creating a river flood relief outlet and reducing flood risk to New Orleans. 的 波西米亚溢洪道 was completed in the Fall of 1926 by the Orleans Levee District with the removal of the artificial Mississippi River levees, 值得一提的是，就在1927年大洪水爆发的两个月前. 的 spillway has a broad elevated river bank (natural levee) that slopes gently to the marsh and to Breton Sound. 自1926年以来, the natural levee of the 波西米亚溢洪道 has been periodically overtopped 在洪水 on the Mississippi River.
路易斯安那州普拉克明教区波希米亚溢洪道的位置. 泄洪道长达11英里，1926年在这里拆除了防洪堤. When the river rises, water overtops the natural levee and water spills into the forests and marshes.
研究波西米亚溢洪道提供了一个观察自然过程的机会. 在大堤建成之前, 在洪水, the river would overtop the natural levee of the Mississippi River and water would spill into the adjacent forests and wetlands. 而河流的现状(最大流量, sediment load) and the receiving basin (presence of canals and trenasses) have changed over time, the 波西米亚溢洪道 still offers a glimpse into the past of the way the river may have operated before human intervention. It also offers a glimpse at the historical interaction between the river and the wetlands before the river levees were built. 的 spillway also allows us to see the effects of pulsed overbank flow on wetlands which may inform future operation of river diversions.
密西西比河上涨时，波希米亚溢洪道就会溢出, 创造有趣的学习过程. 在一些地方(左上)，溢顶导致了向上游的侵蚀。, 随着河水上涨，贯穿泄洪道的道路开始溢出(右上)。, the forest along the natural levee becomes flooded when the river rises (bottom left) and the road becomes flooded completely when the river stage is high.
PC has been investigating the spillway since 2007 and in this time was able to study the effects of the floods of 2008 and 2011. In 2010 a survey was conducted of the Bohemia Road that runs the length of the spillway along the natural levee. This allowed us to determine (for the most part) the controlling elevation for overtopping along the length of the spillway. 换句话说, the elevation of the natural levee (in most cases the road) would be the elevation the river would need to top for the spillway to flow water. 2011年洪水期间，我们对溢洪道进行了广泛的水文调查. 这项调查的结果可以在我们题为"路易斯安那州东南部的波西米亚溢洪道:历史, 一般的描述, 2011年水文调查”(电子邮件 info@ScienceForOur海岸.org (复印一份)此外还有溢洪道的水文情况, 我们还进行了地貌分析和2010年植被调查. Additionally we used a novel technique to closely analyze the land loss and land gain in the spillway over time.
We conducted extensive research during the 2011 Mississippi River flood by walking the entire 11 mile road that runs the length of the spillway. 在一些地方, 水几乎齐腰高(左上), 我们用一个有标记的PVC杆测量不同地点的水深, 这是与河流阶段相关的(右上), we measured flow with a flow meter where it was deep enough (bottom left) and we used an orange to measure flow in shallow locations by timing how long it tool the orange to travel a certain distance (bottom right). 的 pink ribbon helped determine direction of flow by recording compass direction lined up with the ribbon (bottom right).
It was discovered during the 2011 Mississippi River flood survey that overtopping waters were captured quickly by small natural channels, 洪水漫过天然堤坝后不久就形成了沟槽和沟渠. 坡面流较少, 在天然堤坝旁的森林里，没有到达邻近的沼泽地.
It was also discovered through our land loss analysis from 1932 to 2010 that there have been low land loss rates in the spillway since 1975. Most of the land loss that occurred before 1975 is from the dredging of oil and gas and navigation canals and borrow pits. 的 波西米亚溢洪道 does not seem to suffer the same interior land loss due to subsidence as other parts of the coast. This stability may be the result of periodic pulses of water received from the Mississippi River 在洪水 but could also be due to underlying geology, 或者两者的结合.
1932年至2010年，波希米亚溢洪道的土地流失. Notice there is little land loss except what is associated with canal dredging and shoreline erosion.
在我们广泛的调查中, 我们还观察到航运和油气运河填充, 这在路易斯安那州南部很罕见. 人工运河的存在通常会加强海水入侵的侵蚀, 海浪能量增加，将风暴潮引向内陆.
波西米亚溢洪道的运河正在进行填筑. This is a rare occurrence in southeast Louisiana where canals usually expand and contribute to interior marsh loss.
的 vegetation survey revealed that the patterns at the 波西米亚溢洪道 are what to be expected given the environment. 的 narrow swath of forest present along the Mississippi River resides on the natural river levee and is therefore at a slightly higher elevation than the adjacent marsh. 海拔, 当一个人离开河流, drops quickly and the landscape quickly grades into a narrow band of scrub/shrub and then into expansive marshes. 的 species composition in the brackish and salt marshes is typical of these environments in Louisiana.
波西米亚溢洪道中的植物群落. 典型的沿河地区, 海拔较高的天然防洪堤上有一片橡树/朴树林, 然后迅速进入沼泽.
通过我们的观察和研究, we have concluded that the pulsed flow from the Mississippi River in flood years since 1926 has contributed to the sustainability and resiliency of marshes in the 波西米亚溢洪道.
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路易斯安那州东南部的波西米亚溢洪道:历史, 一般的描述, 2011年水文调查