Search USGS⌕ Search

Geology topics

T. E. A. Van Hylckama

Publications and source records attributed to T. E. A. Van Hylckama.

4 recordsLinked to original sources
USGS2009

Water, something peculiar

Some chemical and physical properties of water are discussed and compared with those of other fluids. For instance, the boiling point is much higher than one would expect considering the molecular weight of water. The heat capacity is also much higher but the viscosity is not. The dielectric constant is exceptionally high. These and other properties of water can be explained by the geometry of the water molecule and the structure of water or ice.

Hydrological Sciences Bulletin↗
USGS1970

Winds over saltcedar

An analysis of hourly wind speeds above and within a stand of saltcedar near Buckeye, Arizona, reveals that in 90% of all observed cases, the wind profiles above the stand can be represented by the simple logarithmic equation: u z = u* k 1 n "> uz=u*k1n ( z z 0 ) "> zz0) where u z is the velocity at height z. The roughness length (z 0 ), (disregarding zero displacement), varies with a stability ratio similar to Richardson's number. The friction velocity, u* , depends on the wind speeds above the vegetation. Von Karman's constant, k, equals 0.41. Within the thickets there is considerable turbulence, and irregular wind inversions occur during daylight hours. The results are important for estimating water losses by evapotranspiration by either the energy-budget or the mass-transfer formulae.

Arizona↗
USGS1970

Estimating steady-state evaporation rates from bare soils under conditions of high water table

A procedure that combines meteorological and soil equations of water transfer makes it possible to estimate approximately the steady-state evaporation from bare soils under conditions of high water table. Field data required include soil-water retention curves, water table depth and a record of air temperature, air humidity and wind velocity at one elevation. The procedure takes into account the relevant atmospheric factors and the soil's capability to conduct 'water in liquid and vapor forms. It neglects the effects of thermal transfer (except in the vapor case) and of salt accumulation. Homogeneous as well as layered soils can be treated. Results obtained with the method demonstrate how the soil evaporation rates·depend on potential evaporation, water table depth, vapor transfer and certain soil parameters.

Open-File Report↗