Electronic Theses and Dissertations


Open Access Thesis


Wind power--Environmental aspects--Iowa; Surface roughness; Aerodynamics;


Wind energy development shows a rapid growth in the United States. This renewable energy source not only mitigates environmental concerns by reducing greenhouse gas emission, but also provides energy independence. Wind is clean and abundant, and is one of the most promising sources of alternative energy. Iowa is among the top wind energy producers in the nation, it is third by installed capacity and first in per capita production. In order to utilize wind resource potential most efficiently, accurate wind resource assessments are required. Changes in the aerodynamic characteristics of a site can have a major influence on the wind regime at the surface/air interface. Estimation of hub height wind speed and thus, available wind resources, may be influenced by the values chosen for zero-plane displacement and surface roughness length (Z0). Aerodynamic roughness (Z0) is a widely used parameter describing the effective roughness of a surface to fluid flow. This study was conducted to identify surface roughness coefficients for corn and soybeans and determine the effect of seasonal change of crops on Z0. Ten minute average wind speed data together with wind direction, measured over a 35 day period above a corn and soybeansfield near Ames, IA, were used to determine Z0 coefficients. Hub height wind speed was calculated using table values of surface roughness and Z0 derived from observations. Obtained values of surface roughness and hub height wind speed were compared to each other using independent sample t-test. Significant difference was found between predefined Z0 and Z0 derived from wind profiling. This leads to discrepancy in resulting hub height wind speed calculated using measurement based Z0 and traditional assumptions using table values of roughness. Also, a growing trend in seasonal surface roughness change was identified. The results highlight the importance of improving aerodynamic roughness parameterization of vegetation. Research suggests that the use of enhanced Z0 coefficients could improve wind resource characterization and would be beneficial for use in wind farm site suitability models.

Date of Award


Degree Name

Master of Arts


Department of Geography

First Advisor

Andrey N. Petrov

Date Original


Object Description

1 PDF file (ix, 111 pages)



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