Location of 24 extensometers used to measure compaction in the Central Valley

This digital dataset describes the location of 21 extensometers used for observations of subsidence in the Central Valley Hydrologic Model (CVHM). The Central Valley encompasses an approximate 50,000 square-kilometer region of California. The complex hydrologic system of the Central Valley is simulated using the USGS numerical modeling code MODFLOW-FMP (Schmid and others, 2006). This simulation is referred to here as the CVHM (Faunt, 2009). Utilizing MODFLOW-FMP, the CVHM simulates groundwater and surface-water flow, irrigated agriculture, land subsidence, and other key processes in the Central Valley on a monthly basis from 1961-2003. The total active modeled area is 20,334 square-miles. Water levels, water-level altitude changes, and water-level and potentiometric-surface altitude maps; streamflows; boundary flows; subsidence; groundwater pumpage; water use; and water-delivery observations were used to constrain parameter estimates throughout the calibration of the CVHM. Measured compaction from data collected by extensometers in the valley was used as a subsidence calibration target. Subsidence monitoring observations can provide valuable information about hydrologic parameters such as elastic and inelastic skeletal specific storage. The CVHM was adjusted to fit the range of measured compaction at the extensometer sites utilizing UCODE-2005 (Poeter and others, 2006) and manual calibration. The calibration target was the measured compaction from several extensometers in the region. Compaction though delayed drainage and re-pressurizing of aquitards was not simulated. The CVHM is the most recent regional-scale model of the Central Valley developed by the U.S. Geological Survey (USGS). The CVHM was developed as part of the USGS Groundwater Resources Program (see "Foreword", Chapter A, page iii, for details).

本数字数据集记录了用于加州中央山谷水文模型（Central Valley Hydrologic Model, CVHM）地面沉降观测的21台伸长计的布设位置。该山谷位于美国加利福尼亚州境内，总面积约5万平方千米。加州中央山谷复杂的水文系统采用美国地质调查局（U.S. Geological Survey, USGS）的数值模拟代码MODFLOW-FMP进行模拟（Schmid等，2006），本模拟即为本研究中所称的CVHM模型（Faunt，2009）。借助MODFLOW-FMP代码，CVHM模型以月为时间步长，模拟了1961—2003年间加州中央山谷的地下水与地表水径流、灌溉农业、地面沉降及其他关键水文过程。模型的有效模拟总面积为20334平方英里。在CVHM模型的全流程率定过程中，水位、水位高程变化、水位与测压面高程分布图、径流量、边界流量、地面沉降量、地下水抽采量、用水量及输水观测数据均被用于约束参数估算。本山谷内通过伸长计采集得到的实测压密量，被用作地面沉降率定的目标值。地面沉降监测观测数据可为水文参数估算提供关键支撑，例如弹性与非弹性骨架比储水系数。研究人员借助UCODE-2005软件（Poeter等，2006）结合手动率定，对CVHM模型进行调整，以匹配各伸长计测点处的实测压密量范围。本次率定的目标为该区域内多台伸长计采集的实测压密量。本模型未模拟通过弱透水层延迟排水与再加压过程产生的压密现象。CVHM模型是美国地质调查局（U.S. Geological Survey, USGS）开发的最新一代加州中央山谷区域尺度水文模型。该模型作为美国地质调查局地下水资源计划的一部分开发完成，详细信息可参见"前言"A章节第iii页。