Alexander O. Headman Jory S. Hecht 20240214 2.0 tabular digital data Reston, Va. U.S. Geological Survey https://doi.org/10.5066/P922P61Z The U.S. Geological Survey (USGS) Water Resources Mission Area (WMA) is working to address a need to understand where the Nation is experiencing water shortages or surpluses relative to the demand for water need by delivering routine assessments of water supply and demand and an understanding of the natural and human factors affecting the balance between supply and demand. A key part of these national assessments is identifying long-term trends in water availability, including groundwater and surface water quantity, quality, and use. An understanding of the impacts of reservoirs on water availability is essential for this assessment. This data release contains decadal time series of cumulative normal reservoir storage capacity upstream of U.S. Geological Survey streamgages in the National Water Information System (NWIS) conducted as part of the U.S. Geological Survey's Integrated Water Availability Assessment (IWAAs) Trends & Drivers project. These data were used to identify post-reservoir construction periods of record at these streamgages for Mann-Kendall gradual trend analyses of streamflow and stream temperature records contingent upon a subsequent screening for post-reservoir construction record completeness. This data release builds on a prior data release containing cumulative upstream reservoir storage capacity data and flow-regulation metrics (Wieczorek et al., 2018) (https://doi.org/10.5066/F7765D7V ), the National Inventory of Dams (for dam construction dates and other information about individual dams), and the IWAAs Trends and Drivers database. In particular, the Wieczorek et al. (2018) data release provides decadal cumulative storage capacity upstream of streamgages from 1930 to 2010 as well as additional information for 2013. We combine this decadal time series information with completion dates of individual dams to identify the last year during which a major change in reservoir storage took place. Abrupt changes in reservoir storage are identified using storage ratios, which we define as the ratio of cumulative upstream reservoir normal storage capacity to mean annual streamflow between 1980 and 2020. Decades during which the storage ratio increases by more than 10% of mean annual streamflow are identified. Next, to determine the final year of dam construction, we examine the years of completion for all dams constructed upstream of a streamgage in a given decade. Any individual dam which increases the storage ratio by more than 5% of mean annual streamflow, then the last year in which a dam producing such an increase is considered the end of the construction period and the post-reservoir discharge record starts the following year. Sites that did not experience an increase in storage ratio greater than 10% in a single decade but had cumulative increase above 10% were flagged but their records were not truncated. Records at streamgages that already had a storage ratio above 10% in 1930, the first year for which decadal cumulative upstream storage capacity data from Wieczorek et al. (2018) are available but did not exhibit any subsequent decadal increase in storage ratio above 0.10, were truncated to start in 1930. Three key assumptions underpin this analysis: 1. Reservoirs are assumed to have been filled within a year after dam construction was completed and, thus, the start of the year of the post-reservoir construction trend period is one year after the year of completion. This assumption may not reflect the multi-year filling periods of many large reservoirs in regions with high interannual precipitation variability. 2. Identification of a single post-reservoir construction period for trend analysis implicitly assumes that reservoir operating policies remained consistent throughout this period and no subsequent changes in storage following dam construction. 3. The storage ratios based on flows at gages downstream of dams between 1980 and 2020 are assumed to be unaffected by any changes in streamflow due to dams or changes in climate and other environmental conditions. Given that dams tend to reduce mean annual streamflow through forced evaporation and water withdrawals, we assume dam impacts lower the naturally occurring mean annual streamflow. Consequently, such storage ratios will become higher if dams lower mean annual flows, making our storage ratio estimates used to identify dam-impacted sites conservative. To identify streamgages with streamflow substantially affected by dams, and then identify post-dam construction periods of record at each streamgage for trend analyses and other uses. This time period information reflects reservoirs upstream of USGS streamgages between 1930 and 2013. Subsequent updates to this data release will accommodate the construction, modification and removal of reservoirs upstream of USGS streamgages. 1930 2013 See Supplemental Info Complete None planned -178.5938 179.7700 71.3889 18.4656 ISO 19115 Topic Category inlandWaters USGS Metadata Identifier USGS:64f8d595d34ed30c20546a56 None United States CONUS None. Please see 'Distribution Info' for details. None. Users are advised to read the dataset's metadata thoroughly to understand appropriate use and data limitations. Alexander O Headman U.S. Geological Survey, NW-PACIFIC ISLAND REG Geographer mailing address

934 Broadway

Tacoma WA 98402 US 253-552-1613 253-552-1581 aheadman@usgs.gov No formal logical accuracy tests were conducted No formal logical accuracy tests were conducted Data set is considered complete for the information presented, as described in the abstract. Users are advised to read the rest of the metadata record carefully for additional details. United States Geological Survey 20231001 application/service https://www.usgs.gov/national-hydrography/national-hydrography-dataset Digital and/or Hardcopy 19000101 20230713 publication date NLDI Provides ComID and upstream linkages between dams and sites. Michael E Wieczorek David M Wolock Peter M McCarthy 2021 dataset https://www.sciencebase.gov U.S. Geological Survey https://doi.org/10.5066/p92s9zx6 Digital and/or Hardcopy 18800101 20131231 publication date Wieczorek et al. (2021) All dam metrics assigned to NHD flow routing. United State Army Corps of Engineers 20231001 vector digital data https://nid.sec.usace.army.mil/#/ Digital and/or Hardcopy 18800101 20181231 publication date NID metadata concerning dams, their capacity, name, location and construction. U.S. Geological Survey 1994 dataset https://www.sciencebase.gov U.S. Geological Survey https://doi.org/10.5066/f7p55kjn Digital and/or Hardcopy 18600331 20230331 ground condition NWIS Streamflow information, upstream drainage area. Methods of data production are documented as part of the software repository at https://code.usgs.gov/water/IWAAs-trends/trends-analysis/reservoir_impacts. A master script, _main.R, calls a sequence of five functions, each of which are contained in their own scripts: (1) fn_clean_nid_2018.R Formats and prepares NID data for interoperability with NWIS records and IWAA datasets. (2) fn_dams.R - combines NID (2018) database information (updated through 2016) with Wieczorek et al. (2018) data release (https://code.usgs.gov/water/IWAAs-trends) containing information about the number of dams upstream of USGS streamgages along with their cumulative storage capacity at decadal intervals from 1930 to 2010 along with 2013. (3) fn_site_flagging.R - uses the National Hydrolinked Data Index (NLDI)https://www.sciencebase.gov/catalog/item/58c301f2e4b0f37a93ed915a (https://waterdata.usgs.gov/blog/nldi-intro/) to provide ComIDs and retrieve upstream dam information for each streamgage. (4) fn_network_trace.R - uses the National Hydrolinked Data Index (NLDI) (https://waterdata.usgs.gov/blog/nldi-intro/) to identify dams upstream of each streamgage. All gages on the same ComID as dams are assumed to be located downstream of all dams on that ComID. (5) fn_post_reservoir_record_management.R (also calls fn_timeseries.R) - computes decadal storage ratio (cumulative upstream normal-pool reservoir capacity/annual mean flow) at each streamgage (1930-2010, 2013) and then identifies the last year of major change in cumulative reservoir storage capacity upstream of a streamgage. 20240731 Alexander O Headman U.S. Geological Survey, NW-PACIFIC ISLAND REG Geographer mailing address

934 Broadway

Tacoma WA 98402 US 253-552-1613 253-552-1581 aheadman@usgs.gov decadal_storage_above_sites_db.csv Comma Separated Value (CSV) file containing data. Producer Defined site_id National Water Information System Identifier Producer Defined ID field assigned by U.S. Geological Survey as part of the National Water Information System. decade End of the decade (###0) where cumulative upstream normal storage capacity and storage ratio are calculated. Data from 2013 also provided. Producer Defined 1930 2013 year storage_ratio Ratio of cumulative upstream reservoir storage capacity to annual inflow Producer Defined NA No Data Producer defined 0.0 252.392798837984 unitless ratio cum_normal_storage Cumulative normal storage capacity of all upstream reservoirs listed in the National Inventory of Dams. Producer Defined NA No Data Producer defined 0.0 161200023.38 acre-feet dam_site_links_db.csv R Data Serialization file containing data. Producer Defined nidid National Inventory of Dams ID Producer Defined ID assigned by the U.S. Army Corps of Engineers as part of the National Inventory of dams. site_id National Water Information System Identifier Producer Defined ID field assigned by U.S. Geological Survey as part of the National Water Information System. dam_storage_impacts_by_site_db.csv R Data Serialization file containing data. Producer Defined site_id National Water Information System Identifier Producer Defined ID field assigned by U.S. Geological Survey as part of the National Water Information System. poi_type_id Period of interest type for trend analysis Producer defined longest_possible_period Longest possible period through 2022 (exact end day depends on year_type_id) for computing trends at a given streamgage for which data are sufficiently complete for trend computations. Producer defined fixed_1980_2020 41-year period running from 1980-2020. Data must meet criteria for trends to be run. See rl_complete_criterion_id for more on completeness criteria. Producer defined fixed_1990_2020 31-year period running from 1990-2020. Data must meet criteria for trends to be run. See rl_complete_criterion_id for more on completeness criteria Producer defined fixed_2000_2020 21-year period running from 2000-2020. Data must meet criteria for trends to be run. See rl_complete_criterion_id for more on completeness criteria. Producer defined year_last_big_change Year of the last significant storage change upstream of site_id Producer Defined NA the last year a dam increasing the cumulative upstream storage ratio by more than 0.05 (5%) during a decade in which this ratio increases by more than 0.10 (10%). If no single dam increases the storage ratio by more than 0.05 during a decade in which the storage ratio increases by more than 0.10, then this year becomes the last year during which any dam upstream of the streamgage was constructed. Producer defined 1931 2010 Year start_year_mod The modified start year for the streamgage record that only encompasses the post-reservoir construction period. If there is no substantial change in reservoirs impacts to streamflow during the period of record, then start_year_mod is equal to the start year of a given trend period of interest type (poi_type_id) at a given streamgage (site_id). Producer Defined 1877 2020 flag_storage_change Flag indicating if storage change occurred at or upstream of site_ID Producer Defined NA No Data Producer defined FALSE The change in storage ratio between 1930 and 2013 did not exceed 0.10 (10%). Producer defined TRUE The change in storage ratio between 1930 and 2013 did exceed 0.10 (10%). Producer defined com_id Common identifier from medium resolution National Hydrology Dataset. Producer Defined -9999 No Data Producer defined Common identified from medium-resolution National Hydrology Dataset Plus (NHDPlus). Represents a unique ID. com_dam_flag A dam exists on the same ComID as the site_id. Producer Defined False Dam does not exist on ComID Producer defined True dam exists on ComID Producer defined major_dam_flag A major dam (as defined by the National Inventory of Dams) exists upstream of the site_id location. Producer Defined NA No Data Producer defined FALSE No major dams upstream of site_id Producer defined TRUE Major dam upstream of site_id exists. Producer defined da_nwis_sqmi Upstream drainage area of NWIS site Producer Defined NA No Data Producer defined 0.03 1144500.0 square miles individual_dam_storage_db.csv Comma Separated Value (CSV) file containing data. Producer Defined nidid National Inventory of Dams ID Producer Defined Unique identifier assigned by the Army Corps of Engineers as part of the National Inventory of dams. dam_name Name of dam Producer Defined NA No Data Producer defined Name of the dam as recorded by the National inventory of Dams. year_complete Year dam construction was completed Producer Defined 1640 2017 da_nid_sqmi Upstream area impounded by the dam Producer Defined 0.0011012241882062 2043297.08576563 normal_storage Volume of water in a reservoir below the normal retention level. Producer Defined 0.01 28255000.0 acre-feet dam_comid ComID dam is located on. Producer Defined Common identified from medium-resolution National Hydrology Dataset Plus (NHDPlus). Represents a unique ID. latitude Latitude Producer Defined NA No Data Producer defined 25.360001 48.9959 degrees longitude Longitude Producer Defined NA No Data Producer defined -124.4920578 -67.08975 degrees GS ScienceBase U.S. Geological Survey mailing address

Denver Federal Center, Building 810, Mail Stop 302

Denver CO 80225 United States 1-888-275-8747 sciencebase@usgs.gov Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty. Digital Data https://doi.org/10.5066/P922P61Z None 20250522 Alexander O Headman U.S. Geological Survey, NW-PACIFIC ISLAND REG Geographer mailing address

934 Broadway

Tacoma WA 98402 US 253-552-1613 253-552-1581 aheadman@usgs.gov FGDC Content Standard for Digital Geospatial Metadata FGDC-STD-001-1998