Streamflow - Small watersheds - Small Watershed 6. Rognel Heights. This is a 7.8 ha urban watershed with no natural drainage network. Samples (weekly grab and flow-weighted composite) are taken in a stormwater drainage pipe BES ID 527-

Participants Gary Fisher, U.S. Geological Survey (oversees stream flow monitoring) Ed Doheny, U.S. Geological Survey (oversees stream flow monitoring) Ken Belt, U.S. Forest Service (oversees weekly station checks) I. Collection of Flow Data at USGS Stream Gage Stations BES stream chemistry samples are collected at gaging stations built and maintained by the U.S Geological Survey and which are funded mainly by LTER funds. However a number of the stations are funded by other sources, including the USGS, Maryland Department of the Environment, Baltimore County DEPRM, and Baltimore City DPW. Stage at each gage site is measured to about 0.01 ft accuracy and is recorded at 15 minute (or shorter) intervals using either a float gage or pressure transducer. These stage records are converted to flow records using stage-discharge relationships (see below). Crest-stage recorders (floating cork gages) indicate high water marks and provide a backup source of high water in case recording gages are compromised in flooding conditions. Stilling wells are installed at each site, either in the channel or via piping to the channel, to provide quiescent locations for sensing of stage. General Approach to Discharge Measurement and Flow Ratings In a measurement of discharge (volumetric flow per unit time), a number of velocity measurements are taken across a transect located near the gage using a wading rod and propeller current meter (usually a mini (pygmy) velocity meter). Velocities (ft/sec) for each sub section are multiplied by their respective sub section areas (sq. ft.) and these discharges (cubic feet per second) are then summed to get a total discharge measurement for the section. Generally, an attempt is made to include enough velocity measurements across the transect such that no more than 10 % of the total discharge is contained in each sub section, although this may not be achievable for higher flows. Each total discharge measurement, along with the concurrent stage reading constitutes a point on a stage-discharge rating curve. Over time, discharge measurements are obtained for a range of stages so that a complete, accurate and current stage-discharge rating curve (graph) can be constructed. USGS field crews visit all sites about every six weeks to download data, check and calibrate equipment, and to do a low flow discharge measurements to check the stage-discharge rating for shifts, and to observe the channel section for potential changes in the high flow rating. A single USGS hydrologist is assigned to the BES stations to provide continuity and to maximize familiarity with the stations. These USGS visits are augmented by weekly visits by BES field crews who do a number of checks under the guidance of a Forest Service Hydrologist (see below, II. Stream Gage calibration & Flow Rating QAQC: Weekly Checks). High flow velocities cannot be measured in-stream, and are metered by USGS crews from bridges near the gaging station. Discharge measurements during runoff events are repeatedly conducted until the high flow portion of the rating is defined. Extremely high flow discharges that cannot be measured are estimated by a slope area curve method using cross section geometry, channel roughness and surveyed elevations of high points of the hydraulic grade line indicated by debris left by the receding limb of the hydrograph. Data are recorded at 15 minute intervals at the larger watersheds and at 5 minute intervals at small watersheds. Records are downloaded electronically and processed at the USGS office where adjustments are made for calibration problems, backwater corrections (due to debris and ice buildup), missing records, shifts in the rating, etc. Small changes in the low flow portion of the stage-discharge rating are handled using参与者包括：加里·费舍尔（Gary Fisher）、美国地质调查局（U.S. Geological Survey, USGS，负责径流监测）；埃德·多赫尼（Ed Doheny）、美国地质调查局（负责径流监测）；肯·贝尔特（Ken Belt）、美国林务局（U.S. Forest Service，负责每周站点巡检）。 一、美国地质调查局水文测站流量数据采集 BES流域化学样品采集点设于由美国地质调查局建设维护的水文测站，此类站点主要由长期生态研究（Long-Term Ecological Research, LTER）经费资助，另有部分站点由其他渠道提供资金支持，包括美国地质调查局、马里兰州环境部、巴尔的摩县环境与资源管理部（DEPRM）以及巴尔的摩市公共工程部（DPW）。 各测站的水位测量精度可达约0.01英尺，采用浮式测尺或压力传感器，以15分钟（或更短）间隔记录数据。上述水位记录将通过水位-流量关系（详见下文）转换为流量记录。洪峰水位记录仪（浮动塞规测尺）可记录高水位标记，作为洪水期间记录仪损坏时的高水位备份数据源。各站点均安装静水井（stilling well），设于河道内或通过管道连接至河道，为水位传感提供平稳的测量环境。 二、流量测量与流量率定通用方法 流量指单位时间内的体积流量，测量时需采用涉水杆（wading rod）和旋桨式流速仪（propeller current meter，通常为微型（侏儒型）流速仪）在测站附近的河道断面上开展多点流速测量。将各子断面的流速（单位：英尺/秒）乘以对应子断面面积（单位：平方英尺），再将所得流量值（单位：立方英尺每秒）求和，即可得到该断面的总流量测量结果。通常会在断面上布设足够多的流速测点，使每个子断面的流量占比不超过总流量的10%，但高流量工况下可能无法满足该要求。 每次总流量测量结果与同步水位读数共同构成水位-流量率定曲线的一个数据点。随着时间推移，针对一系列水位开展流量测量，从而构建完整、准确且时效性强的水位-流量率定曲线（图表）。 美国地质调查局野外人员每约六周到访所有站点，完成数据下载、设备检查与校准，并开展低流量测量以校验水位-流量率定曲线是否发生偏移，同时观测河道断面以评估高流量率定相关的潜在变化。指定一名美国地质调查局水文专家负责BES站点，以保障工作连续性并最大化对站点的熟悉程度。 除美国地质调查局的巡检外，BES野外人员每周开展站点巡检，相关工作在林务局水文专家的指导下进行（详见下文"二、水文测站校准与流量率定质量控制：每周巡检"）。 高流速无法在河道内直接测量，美国地质调查局人员通过测站附近的桥梁开展流速测量。径流事件期间需反复开展流量测量，直至明确率定曲线的高流量段。对于无法直接测量的极端高流量，采用比降面积曲线法进行估算，该方法利用断面几何形态、河道糙率以及由退水段水文过程线（hydrograph）遗留碎屑所指示的水力坡线高点的实测高程。 大型流域的数据以15分钟间隔记录，小型流域则以5分钟间隔记录。数据通过电子方式下载并在美国地质调查局办公室进行处理，针对设备校准问题、回水校正（backwater correction，由河道碎屑堆积与冰堵引发）、缺失数据记录、率定曲线偏移等问题开展调整。水位-流量率定曲线低流量段的小幅调整采用[原文未完整提供后续内容]。