GAGES-II: Geospatial Attributes of Gages for Evaluating Streamflow

This dataset, termed "GAGES II", an acronym for Geospatial Attributes of Gages for Evaluating Streamflow, version II, provides geospatial data and classifications for 9,322 stream gages maintained by the U.S. Geological Survey (USGS). It is an update to the original GAGES, which was published as a Data Paper on the journal Ecology's website (Falcone and others, 2010b) in 2010. The GAGES II dataset consists of gages which have had either 20+ complete years (not necessarily continuous) of discharge record since 1950, or are currently active, as of water year 2009, and whose watersheds lie within the United States, including Alaska, Hawaii, and Puerto Rico. Reference gages were identified based on indicators that they were the least-disturbed watersheds within the framework of broad regions, based on 12 major ecoregions across the United States. Of the 9,322 total sites, 2,057 are classified as reference, and 7,265 as non-reference. Of the 2,057 reference sites, 1,633 have (through 2009) 20+ years of record since 1950. Some sites have very long flow records: a number of gages have been in continuous service since 1900 (at least), and have 110 years of complete record (1900-2009) to date.

The geospatial data include several hundred watershed characteristics compiled from national data sources, including environmental features (e.g. climate – including historical precipitation, geology, soils, topography) and anthropogenic influences (e.g. land use, road density, presence of dams, canals, or power plants). The dataset also includes comments from local USGS Water Science Centers, based on Annual Data Reports, pertinent to hydrologic modifications and influences. The data posted also include watershed boundaries in GIS format.

This overall dataset is different in nature to the USGS Hydro-Climatic Data Network (HCDN; Slack and Landwehr 1992), whose data evaluation ended with water year 1988. The HCDN identifies stream gages which at some point in their history had periods which represented natural flow, and the years in which those natural flows occurred were identified (i.e. not all HCDN sites were in reference condition even in 1988, for example, 02353500). The HCDN remains a valuable indication of historic natural streamflow data. However, the goal of this dataset was to identify watersheds which currently have near-natural flow conditions, and the 2,057 reference sites identified here were derived independently of the HCDN. A subset, however, noted in the BasinID worksheet as “HCDN-2009”, has been identified as an updated list of 743 sites for potential hydro-climatic study. The HCDN-2009 sites fulfill all of the following criteria:
(a) have 20 years of complete and continuous flow record in the last 20 years (water years 1990-2009), and were thus also currently active as of 2009,
(b) are identified as being in current reference condition according to the GAGES-II classification,
(c) have less than 5 percent imperviousness as measured from the NLCD 2006, and
(d) were not eliminated by a review from participating state Water Science Center evaluators.

The data posted here consist of the following items:- This point shapefile, with summary data for the 9,322 gages.- A zip file containing basin characteristics, variable definitions, and a more detailed report.- A zip file containing shapefiles of basin boundaries, organized by classification and aggregated ecoregion.- A zip file containing mainstem stream lines (Arc line coverages) for each gage.

本数据集命名为"GAGES II"，全称为河流水位站评估地理空间属性 第二版（Geospatial Attributes of Gages for Evaluating Streamflow, version II），为美国地质调查局（U.S. Geological Survey, USGS）维护的9322个河流水位站提供地理空间数据与分类信息。该数据集是原版GAGES的更新版本，原版GAGES于2010年发表于《Ecology》期刊官网的数据论文（Falcone等人，2010b）。

GAGES II数据集包含的水位站需满足以下任一条件：自1950年起拥有至少20个完整年度（无需连续）的流量观测记录；截至2009水文年仍处于运行状态，且其流域位于美国境内（包括阿拉斯加、夏威夷与波多黎各）。参考水位站的遴选依据为：基于美国12个主要生态区的大区域框架，其所在流域为受干扰程度最低的区域。在全部9322个监测站点中，2057个被归类为参考站点，7265个为非参考站点。在2057个参考站点中，有1633个截至2009年拥有自1950年起的20年以上观测记录。部分站点拥有极长的水文序列：有多个水位站自1900年起便持续运行至今，完整记录时长可达110年（1900年至2009年）。

该地理空间数据包含数百项从国家级数据源汇编得到的流域特征指标，涵盖环境特征（如气候——包括历史降水、地质、土壤、地形）与人为影响因素（如土地利用、道路密度、水坝、运河或发电厂的分布）。数据集还包含美国地质调查局当地水科学中心基于年度数据报告出具的、与水文改造及影响相关的注释信息。本次发布的数据还包含GIS格式的流域边界数据。

本数据集与美国地质调查局水文气候数据网络（Hydro-Climatic Data Network, HCDN；Slack与Landwehr，1992）性质不同，后者的数据评估截止至1988水文年。HCDN遴选的水位站在其历史中曾存在代表天然流量的观测时段，并标注了天然流量对应的观测年份（例如，即便在1988年，也并非所有HCDN站点都处于参考状态，如站点编号02353500）。HCDN仍是历史天然河流水文数据的宝贵参考源。然而，本数据集的目标是遴选当前接近天然流量状态的流域，本次确定的2057个参考站点均独立于HCDN生成。不过，其中一个以"HCDN-2009"标注于BasinID工作表的子集，被确定为用于潜在水文气候研究的743个更新站点列表。HCDN-2009站点需满足以下全部标准：
(a) 近20年（1990-2009水文年）拥有完整连续的20年流量观测记录，且截至2009年仍处于运行状态；
(b) 根据GAGES-II分类标准，被确定为当前处于参考状态；
(c) 基于2006年全国土地覆盖数据集（National Land Cover Database, NLCD 2006）测算的不透水面占比低于5%；
(d) 未被参与评估的各州水科学中心评审排除。

本次发布的数据包含以下内容：
- 包含9322个水位站汇总数据的点形状文件（point shapefile）；
- 包含流域特征、变量定义及详细报告的压缩包；
- 包含按分类与聚合生态区组织的流域边界形状文件的压缩包；
- 包含各水位站干流河道线（Arc line coverages）的压缩包。