Surface Water

Stream Discharge Measurement

Alaska has the greatest surface water resources of any state in the United States. Approximately 40% of the all the surface water outflow for the entire U.S. comes from Alaska. The state receives an average of approximately 1,050,000 million gallons per day (Mgal/d) in the form of precipitation. The Yukon, Kuskokwim, and Copper Rivers are among the ten largest rivers in the U.S., and the state has over 3 million lakes. The Alaska Hydrologic Survey collects, analyzes, and interprets surface water data for the citizenry of Alaska. Listed below are additional facts related to the surface waters of Alaska.

  • Many of Alaska's lakes and streams are frozen, or partially frozen, for five-six months of the year. In late April and May, "breakup" occurs when the snow melts, and the lakes and streams thaw.
  • A typical Alaska stream experiences low flows from December through March, peak flows during breakup in May-June, lower summer flows in July and August, secondary peak flows produced by rainfall in September-October, and declining flows in November.
  • Glaciers significantly influence most of Alaska's major rivers, even though glaciers cover just 5% of the state. For example, glaciers cover only 5% of the Tanana River drainage basin, yet glacial meltwater accounts for half of the river's runoff.
  • Surface water supplies approximately 75%, or about 300 Mgal/d, of the state's water needs for industry, agriculture, mining, fish processing, and public water use.
  • Surface water is used for about half of Alaska's domestic water supply.
  • Hydroelectric powerplants use approximately 1,400 Mgal/d of surface water to generate 20% of the state's electricity.
  • Even with all of the surface water in Alaska, a number of communities experience water quantity problems because of inadequate supplies (especially in permafrost regions), lack of satisfactory distribution systems, and droughts.
  • Flooding and erosion are responsible for millions of dollars of property damage each year. Most of the flooding that occurs in Alaska results from:
    • Rainfall
    • Snowmelt
    • Ice jams clogging stream channels, backing up flow, causing upstream flooding.
  • Glacial outburst floods: nearly 750 glacier-dammed lakes have been identified in Alaska; if the glacial ice dam fails, lake water is released resulting in downstream flooding.
  • Flooding can also be caused by the rapid melting of snow and ice during volcanic eruptions.
  • Alaska's surface waters include over 15,000 anadromous streams (that is, they support runs of spawning seagoing fish, including salmon).
  • Surface water instream flow can be appropriated to support fish and wildlife habitat.

The Division of Mining, Land and Water, Water Management Section, oversees the management and appropriation of Alaska's surface water.