This report summarizes estimates of “natural” and “unimpaired” flows for all areas in the Central Valley tributary to the Sacramento – San Joaquin Delta (Delta) for the period spanning water years 1922-2014. A major objective of this report is to clarify the conceptual differences between natural and unimpaired flows. In spite of the Department’s previous attempts to distinguish between natural conditions and its calculation of theoretical unimpaired flows, unimpaired flow estimates have frequently been used as a surrogate measure of natural conditions, presumably because natural flow estimates were unavailable. This report contains the Department’s first published estimates of natural flows; these estimates are derived from complex simulation models and are based on published estimates of natural vegetation cover and associated evapotranspiration.

This report summarizes estimates of “natural” and “unimpaired” flows for all areas in the Central Valley tributary to the Sacramento – San Joaquin Delta (Delta) for the period spanning water years 1922-2014. A major objective of this report is to clarify the conceptual differences between natural and unimpaired flows. In spite of the Department’s previous attempts to distinguish between natural conditions and its calculation of theoretical unimpaired flows, unimpaired flow estimates have frequently been used as a surrogate measure of natural conditions, presumably because natural flow estimates were unavailable. This report contains the Department’s first published estimates of natural flows; these estimates are derived from complex simulation models and are based on published estimates of natural vegetation cover and associated evapotranspiration.

The dataset contain estimates of natural monthly streamflow for 135,118 stream segments in California, USA, from 1950 to 2012. Segments are identified per the medium resolution National Hydrography Dataset (NHD), Version 1. The dataset also contains observed monthly streamflows and estimates of natural monthly streamflows for 894 USGS stream gages in California, USA.

The dataset contain estimates of natural monthly streamflow for 135,118 stream segments in California, USA, from 1950 to 2012. Segments are identified per the medium resolution National Hydrography Dataset (NHD), Version 1. The dataset also contains observed monthly streamflows and estimates of natural monthly streamflows for 894 USGS stream gages in California, USA.

This digital dataset contains 61 sets of annual streamflow gains and losses between 1961 and 1977 along Central Valley surface-water network for 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's 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. The CVHM includes complex surface-water management processes. The hydrology of the present-day Central Valley and the CVHM model are driven by surface-water deliveries and associated groundwater pumpage. The Streamflow Routing Package (SFR1) is linked to MODFLOW-FMP to facilitate the simulated conveyance of surface-water deliveries. If surface-water deliveries do not meet the farm-delivery requirement, the FMP invokes simulated groundwater pumping to meet the demand. The surface-water network represents a subset of the entire stream network in the valley. Quantitative observations of streamflow gains and losses were available for 57 reaches of 20 major stream systems in the Central Valley for water years 1961-77 (Mullen and Nady, 1985). These observations were included in parameter estimation process and in the model-fit statistics. 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).

This digital dataset contains 61 sets of annual streamflow gains and losses between 1961 and 1977 along Central Valley surface-water network for 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's 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. The CVHM includes complex surface-water management processes. The hydrology of the present-day Central Valley and the CVHM model are driven by surface-water deliveries and associated groundwater pumpage. The Streamflow Routing Package (SFR1) is linked to MODFLOW-FMP to facilitate the simulated conveyance of surface-water deliveries. If surface-water deliveries do not meet the farm-delivery requirement, the FMP invokes simulated groundwater pumping to meet the demand. The surface-water network represents a subset of the entire stream network in the valley. Quantitative observations of streamflow gains and losses were available for 57 reaches of 20 major stream systems in the Central Valley for water years 1961-77 (Mullen and Nady, 1985). These observations were included in parameter estimation process and in the model-fit statistics. 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).

These data are monthly median observed streamflow from 32 gages in the Central Valley for comparison to the updated Central Valley Hydrologic Model (CVHM2). The locations of these gages are shown in the shape file.

These data are monthly median observed streamflow from 32 gages in the Central Valley for comparison to the updated Central Valley Hydrologic Model (CVHM2). The locations of these gages are shown in the shape file.