{
  "dataset_name": "elevation_beginning_water_year_1961_2026",
  "title": "Great Salt Lake Beginning Water Year Elevation, South Arm and North Arm, 1961-2026",
  "purpose": "Provides beginning-of-water-year elevations for ledger tables. Beginning elevation for a given water year is the October 1 elevation at the start of that water year. Ending elevation for a water year should use the beginning elevation of the following water year.",
  "date_range": "1960-10-01 through 2025-09-30 proxy for 2025-10-01",
  "water_year_range": "1961-2026",
  "datum": "NGVD29",
  "sources": [
    {
      "gage": "South Arm / Saltair",
      "usgs_site": "10010000",
      "source_file": "daily-data-mean * 2.csv"
    },
    {
      "gage": "North Arm / Saline",
      "usgs_site": "10010100",
      "source_file": "daily-data-mean * 3.csv"
    }
  ],
  "methodology": [
    "Select October 1 daily mean elevation for each water year beginning date from 1960-10-01 through 2024-10-01.",
    "For water year 2026, use 2025-09-30 as proxy for 2025-10-01 because 2025-10-01 was unavailable in the provided USGS extract.",
    "Where North Arm observations are missing at the Saline gage in early years, impute North Arm elevation as South Arm elevation minus 1.0 ft, consistent with the ledger convention used for bathymetry calculations."
  ],
  "usage_notes": [
    "For annual accounting tables, beginning elevation for water year N equals the row for water_year N.",
    "Ending elevation for water year N equals the beginning elevation for water_year N+1.",
    "For water year 2025, ending elevation should use the water_year 2026 row based on 2025-09-30 proxy."
  ],
  "fields": [
    {
      "field": "water_year",
      "type": "integer",
      "description": "Water year represented by the beginning elevation. Water year begins October 1 of the prior calendar year."
    },
    {
      "field": "beginning_date",
      "type": "date",
      "description": "Date used for beginning-of-water-year elevation. Normally October 1; 2026 uses 2025-09-30 as proxy because 2025-10-01 was unavailable."
    },
    {
      "field": "south_arm_elevation_ft_ngvd29",
      "type": "number",
      "description": "Great Salt Lake South Arm elevation at Saltair gage, feet NGVD29. Source: USGS daily mean elevation."
    },
    {
      "field": "north_arm_elevation_ft_ngvd29",
      "type": "number",
      "description": "Great Salt Lake North Arm elevation at Saline gage, feet NGVD29. Source: USGS daily mean elevation when observed; early missing values imputed as South Arm minus 1.0 ft."
    },
    {
      "field": "north_arm_method",
      "type": "string",
      "description": "Method for North Arm value: observed or imputed_south_arm_minus_1ft."
    },
    {
      "field": "date_note",
      "type": "string",
      "description": "Notes whether value is an observed October 1 beginning elevation or the 2025-09-30 proxy used for unavailable 2025-10-01."
    }
  ]
}