Base Flow of Michigan Streams

This data set provides estimates of the ground-water contribution to stream flow, frequently referred to as base flow, in cubic feet per second. The baseflow of a stream or river is the amount of groundwater discharged from an aquifer to the watercourse. This discharge occurs year-round, and fluctuates seasonally depending on the level of the water in the aquifer. Baseflow is supplemented by direct runoff during and immediately after precipitation or melt events, resulting in peaks on a hydrograph showing stream flow through time. The process of dividing these peaks into base flow and runoff is called hydrograph separation. Hydrograph separations were completed for all USGS stream- flow gaging stations in Michigan that had more than 10 years of daily records. Sites that were clearly affected by upstream impoundments (lakes, dams) were excluded. No attempt was made to detect or correct for trends in the data. This may lead to some errors in the comparison of streams with data from different time periods if there is an underlying temporal trend in the data, but inclusion of all records in the analysis was necessary to increase the data pool and provide better spatial coverage. Watersheds were delineated for each of the 208 stream-flow gaging stations, and various characteristics of each watershed, such as topographic relief, surficial geology, land cover, growing degree days, annual and winter-season precipitation, and others were tabulated. Regression modeling, described in the Technical Report, was used to estimate the baseflow for each steam segment of the 1:100,000-scale National Hydrography Dataset.本数据集提供了地下水对河道径流的贡献量估算值，该贡献量通常被称为基流（base flow），单位为立方英尺每秒。河道或河流的基流，指含水层向河道排泄的地下水总量。此类地下水排泄常年发生，并随含水层水位的变化呈现季节性波动。在降水或融雪事件发生期间及发生后，直接径流会对基流进行补给，这会在表征河道径流随时间变化的水文过程线（hydrograph）上形成峰值。将此类峰值区分为基流与径流的过程，被称为水文过程线分割（hydrograph separation）。研究人员对密歇根州内所有拥有10年以上日监测数据的美国地质调查局（USGS）河道流量监测站完成了水文过程线分割工作。受上游蓄水设施（湖泊、水坝）显著影响的监测站点被排除在外。本次研究未对数据中的趋势进行识别与校正。若数据中存在潜在的时间趋势，这可能会导致不同时段河道径流数据对比时出现一定误差，但为扩充数据集规模并获得更优的空间覆盖度，将所有记录纳入分析是必要的。研究人员为208个河道流量监测站分别划定了流域，并对每个流域的多项特征进行了制表汇总，这些特征包括地形起伏、表层地质、土地覆被、生长度日（growing degree days）、年降水量与冬季降水量等。本研究采用技术报告中提及的回归模型，对1:10万比例尺国家水文数据集（National Hydrography Dataset）中的每一段河道河段的基流进行了估算。