GEOL 10 LECTURE 19 TODAYS MATERIAL: Supplemental Reading (3 parts) on week 10 website Supplemental Reading (3 parts) on week 10 website Hydrology Hydrology PREVIEW MATERIAL: Hydrology Hydrology

Annual precipitation across the USA during Source: Redrawn with data from the National Atmospheric Deposition Program Brooks et al., Hydrology and the Management of Watersheds, 545 p.

Precipitation is measured with rain gages

methods of calculating the mean rainfall on a watershed: Arithmetic mean Arithmetic mean Thiessen polygon Thiessen polygon Isohyetal Isohyetal Brooks et al., Hydrology and the Management of Watersheds, 545 p.

River Flow (Discharge)

Measurements of stream channel cross sections and velocities needed to estimate the mean velocity of a stream

USGS

Todd Kraemer of Pacific Watershed Associates measures low flow at Jacoby Creek for flow study of 4 creeks in Arcata.

Cross-Section Q measurements are time consuming. It is much easier to simply measure the height of the water surface. This is a manual stream gaging station on the Fitzroy River, Rockhampton, January Note the historical reference to heights of previous floods: 1918, 1954, and 1991.

River “Stage”

River “Q”

Stage-Discharge Rating Curve

The streamflow gage on the Willamette River near Salem, Oregon, is one of many in the Willamette Valley and is typical of the more than 7,000 active USGS gages on streams and rivers in the U.S. and Puerto Rico. Most stations monitor river stage (elevation of the water surface), which is then converted to discharge (flow volume per unit time) by use of a stage- discharge rating curve.

Methods of separating baseflow from stormflow; I and II are different approaches. Brooks et al., Hydrology and the Management of Watersheds, 545 p.

Modelled versus observed water heights for the Mary River at Gympie, Queensland, together with observed rainfall. While there is reasonably good agreement in this instance, as can be seen from the differences between the red and green lines, actual river height can vary from what we expect based on modelled results due to data and model limitations.

“flashy”

Most of the largest known floods of the Quaternary Period resulted from breaching of dams formed by glaciers or landslides. Types: Types: Ice-Dam or Landslide-Dam Failure Ice-Dam or Landslide-Dam Failure Lake Overflow (many kinds) Lake Overflow (many kinds) Volcanic Eruption Volcanic Eruption Ice Jam or Snowmelt Ice Jam or Snowmelt Meteorological/Rainfall (most common) Meteorological/Rainfall (most common)

The late-Pleistocene Missoula floods in the Pacific Northwestern United States were some of the largest ever to have occurred on Earth. The floods resulted from the repeated breaching of an ice dam formed from a lobe of the Cordilleran Ice Sheet that blocked the present-day Clark Fork River and created an immense lake known as glacial Lake Missoula.

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Usoi Dam in Tajikastan, formed by a landslide in 1911, created 16 cubic-kilometer Lake Sarez, the largest lake in the world resulting from a landslide. Five million people live in the valleys downstream of the dam. Even partial breaching of the dam could cause catastrophic flooding. Complete failure of the dam could result in the deadliest natural disaster in human history.