|Abstract or Summary
- Furrow irrigation is the dominant practice for irrigating row crops in the
western Treasure Valley region near Ontario, Oregon. Though improvements
have been made in management practices over the years, excessive runoff and
deep percolation are still important problems contributing to surface water and
Field observations were made during two growing seasons to establish a
data base from which the hydraulic surface irrigation model, SRFR (SRFR, a computer program for simulating flow in surface irrigation, developed at the U.S. Water Conservation Laboratory in Phoenix, Arizona
(Strelkoff, 1991)), could be calibrated. SRFR is a numerical model, based on the principles of open channel
hydraulics coupled with an empirical relationship characterizing furrow intake.
SRFR is an analytical tool, with which the user supplies the physical
parameters (such as furrow shape and furrow intake) and also the management
variables (inflow rate and duration of inflow), and a simulation is conducted based on these conditions. Therefore, this model is a tool which provides insight into furrow irrigation processes. More specifically, SRFR can help answer such questions as which factors at the time of the irrigation are most important in determining irrigation performance. Once calibrated for a given set of conditions, various management strategies may be evaluated as to their relative effectiveness. These strategies may include, but are not limited to, cut-back irrigation, surge irrigation, alternating furrow irrigation, and laser-leveling of
A broad data-base is necessary for model calibration and to develop an understanding of it's limitations. Measurements of furrow intake, stream advance times, inflow and outflow, hydraulic roughness and furrow shape were obtained from several sites and irrigation events. These sites represent several crops, field lengths, field slopes, and soil textures. Using these data, a model calibration procedure was developed which matched irrigation inflow and outflow volumes and stream advance times for a given irrigation event. The calibration procedure is used to help identify those model input parameters that best describe a given irrigation event. This thesis is to provide a broad understanding of furrow irrigation systems in northeast Malheur County, recommended hydraulic parameters for use with SRFR, and the practical limitations of such hydraulic irrigation models.
Irrigation performance is largely determined by the intake characteristics of the soil at the time of irrigation. Field conditions vary greatly depending on the crop, soil moisture, number of irrigations, tractor traffic, field slope, furrow shape and field history. The grower has control over only two variables which determine irrigation performance: inflow rate and duration.
A difference in intake and irrigation performance was found to exist between non-wheel and wheel traffic furrows. These differences became less noticeable late in the season. Straw mulching greatly increases the furrow hydraulic roughness and therefore increases stream wetted perimeter and advance time. Vegetative interference from crops such as potato and sugar beets increase furrow hydraulic roughness late in the season. Initially, furrow shape depends on the crop and which cultivating implement is used. Furrow shape may evolve during the growing season depending on field slope, flow velocities, crop stand and the presence of crop residues and straw mulch.