Science to Inform Management of Floodplain Conservation Lands on the Middle Mississippi River

Within large-river ecosystems, floodplains serve a variety of important ecological functions. A recent survey of 80 managers of floodplain conservation lands along the Upper and Middle Mississippi and Lower Missouri Rivers in the central United States found that the most critical information needed to improve floodplain management centered on metrics for characterizing depth, extent, frequency, duration, and timing of inundation. These metrics can be delivered to managers efficiently through cloud-based interactive maps. To calculate these metrics, we interpolated an existing one-dimensional HEC-RAS hydraulic model for the Middle Mississippi River, which simulated water surface elevations at cross sections spaced (less than 1 kilometer) to sufficiently characterize water surface profiles along an approximately 800 kilometer stretch upstream from the confluence with the Mississippi River over an 80-year record at a daily time step. To translate these water surface elevations to inundation depths, we subtracted a merged terrain model consisting of floodplain LIDAR and bathymetric surveys of the river channel. We completed these calculations for an 800 kilometer stretch of the Missouri River, spanning from Rulo, Nebraska to the river's confluence with the Mississippi River. Analyzed areas include the entirety of the Mississippi River floodplain, with the exception of the St. Louis metropolitan area in which analysis was constrained to currently unleveed areas only. This approach resulted in a 29,000 plus day time series of inundation depths across the floodplain using grid cells with 30 meter spatial resolution. This dataset presents 14 metrics for each of two scenarios, one using a baseline timeseries of stages from the HEC-RAS simulation and one using a timeseries of stages adjusted to account for removal of existing levees from the floodplain. These metrics are calculated on a per pixel basis and encompass a variety of temporal criteria generally relevant to flora and fauna of interest to floodplain managers, including, for example, the average number of days inundated per year within a growing season. We also include the base elevation layer that we generated to calculate depth of inundation from interpolated water-surface elevations.

在大型河流生态系统中，泛滥平原（floodplain）承担着多种关键生态功能。近期一项针对美国中部密西西比河上游、中游以及密苏里河下游沿岸80处泛滥平原保护地管理人员的调研显示，优化泛滥平原管理所需的核心信息，集中于表征洪水淹没深度、范围、频次、持续时长与发生时机的各类指标。上述指标可通过基于云端的交互式地图高效传递给管理人员。为计算上述指标，我们针对密西西比河中游的现有一维HEC-RAS水力学模型进行插值处理：该模型以每日时间步长，在80年的观测序列中，对间距不足1公里的断面处的水面高程进行模拟，以此充分刻画密西西比河汇流点上游约800公里河段的水面形态。为将水面高程转换为淹没深度，我们通过减去融合了泛滥平原激光雷达（LIDAR）与河道水深测量数据的地形模型来实现。我们针对密苏里河从内布拉斯加州鲁洛（Rulo）至其与密西西比河汇流点的800公里河段完成了上述计算。本次分析覆盖密西西比河泛滥平原的全部区域，但圣路易斯都会区除外——该区域的分析仅局限于当前未设防堤的地块。该方法生成了空间分辨率为30米的网格单元对应的泛滥平原淹没深度时序数据，时长超29000天。本数据集包含两种情景下的14项指标：一种采用HEC-RAS模拟得到的基准水位时序数据，另一种则采用针对泛滥平原现有防洪堤拆除情况进行调整后的水位时序数据。上述指标均以单个像素为单位计算，涵盖了泛滥平原管理人员关注的动植物相关的多种时序特征，例如生长季内年均淹没天数。本数据集同时包含我们为通过插值水面高程计算淹没深度而生成的基础高程图层。