Furrow inflow and infiltration variability impacts on irrigation management

Furrow-to-furrow infiltration variability causes nonuniform water absorption rates, furrow stream advance rates, and runoff rates from the furrow tail end. Unevenly set inflow rates to furrows compound these latter two nonuniformities. In order for an irrigator to ensure adequate water advance on a desired portion of furrows, the average inflow rate must be increased. To ensure adequate water application to a desired portion of the furrows, the application time must be extended. Thus, inflow and infiltration variability result in excess water application and reduced irrigation water use efficiency. Models, based on Gaussian distributions of inflow and infiltration, are presented which relate excess furrow irrigation applications to these variabilitie

The Case for Irrigation Tailwater Reuse in Southern Idaho

About half of the irrigated land in southern Idaho is furrow irrigated. With furrow irrigation, a portion of the irrigation water runs off the tail end of the field. Some runoff is necessary to adequately irrigate the whole field. In the Magic Valley, farmers run 20% to 50% of their irrigation water off their fields into tailwater ditches. Twenty percent runoff is about the minimum possible on the local soils and slopes. Fifty percent indicates poor management. Average tailwater runoff from a furrow-irrigated farm is about 40% of the water supplied to the farm

Flow velocity and wetted perimeter effects on furrow infiltration

Infiltration theory and previous studies show that furrow infiltration increases with wetted perimeter. This effect can strongly influence water distribution along furrows. Stagnant blocked-furrow measurements on Portneuf silt loam soil supported this relationship. However, both recirculating infiltrometer and field-scale measurements showed no consistent infiltration:wetted perimeter relationship. The infiltrometer data, collected using a wide range of flow rates on a wide range of slopes, did show infiltration inversely related to flow velocity. This relationship results from the effect of flow on soil aggregate breakdown, particle movement, and depositional seal formation. Because both velocity and wetted perimeter increase with flow rate, their opposing effects on infiltration can result in little apparent effect when flow rates change. These interactions strengthen the inverse relationship between infiltration and furrow slope

Furrow irrigation erosion and sedimentation: On-field distribution

Erosion created by furrow irrigation is a serious problem in some states and has resulted in reduced crop yields. Most furrow erosion assessments have been based on measured sediment discharge from the field, which results in an average erosion rate for the whole field. However, erosion theory predicts that the erosion rate should decrease with distance from the head (inflow) end of the furrow. The purpose of this study was to quantify soil erosion and deposition distribution within furrow irrigated fields. Within field sediment discharge measurements on two silt loam fields in southern Idaho showed that over half of the soil that eroded from the head end of the furrows deposited on the lower portions of the field as furrow flow rates decreased. Erosion rates on the upper quarter of uniformly-sloped furrows were 6-20 times greater than average rates from the field. The measurements demonstrate the need to measure erosion rates on the head ends as well as for the whole field, and explain visible erosion damage from head ends where field average erosion rates are not high

Surface seal influence on surge flow furrow infiltration

The interactive influence of furrow surface seal formation and surge irrigation (intermittent flow) on furrow infiltration into a Portneuf silt loam soil was measured with a recirculating infiltrometer. When the formation of a surface seal was prevented by a layer of cheesecloth laid on the furrow perimeter, flow interruption increased furrow bed bulk density by 100 kg/m3 and decreased infiltration by 25% compared to constant flow. However, on this highly erodible soil, the surface seal which formed on an unprotected perimeter during irrigation reduced infiltration rates by over 50% compared to furrows with a cheesecloth layer. Flow interruption did not increase soil consolidation or decrease infiltration when the normal seal was allowed to form. On the tested soil, surface sealing overshadows the effects of flow interruption on infiltration

Feedback control of cablegation systems

Cablegation is an automated furrow irrigation system (Kemper et al.,1981; Kemper et al., 1985; Kemper et al., 1987) fabricated from gated-pipe, a plug that blocks water flow and slides through the pipe, and a controller that reels out cable to regulate the rate of plug movement. The pipe, with open outlets located near the top of the pipe, is placed on a uniform grade. Water flows through the pipe below the level of the outlets until it reaches the plug where it backs up and flows out of the outlets. Outlets nearest the plug flow at the highest rate, while those further upstream flow at decreasing rates (Figure 1). As the plug moves, the flow is cut back to each furrow. Since each furrow is in a different phase of irrigation, tailwater runoff is fairly constant after an initial starting period

Squeezer: A device for indirect pressure measurement in thin-walled microirrigation tubing

A simple device was developed for measuring pressure in thin—walled collapsible emitting hose or tubing in the field. The device, called a "Squeezer," senses pressure by measuring the force necessary to compress a short section of tubing between two parallel plates to 50% of its original diameter. The force can be measured by either an electronic load cell or a spring balance, and the output, calibrated for a particular size of tubing, read directly in pressure units. The device provides a convenient, non—intrusive and low—cost means for irrigators to assess pressure variations within their microirrigation laterals without installing special fittings or puncturing the tubing

Cablegation evaluation methodology

Cablegation is an automated furrow irrigation system in which the irrigation set moves at a slow, constant rate across the field. This constant movement allows time and space to be interrelated, which simplifies collection of furrow irrigation evaluation data. Specialized cablegation evaluation procedures are described and illustrated. Furrow stream advance and recession times and tailwater runoff rates can be measured at any point in time. Thus, average infiltrated depth and infiltration opportunity time can be easily determined. Water distribution uniformity can be estimated from infiltration rate at the time recession begins and infiltration opportunity times. The infiltration function can be estimated from average infiltrated depth and final infiltration rat

Evaluating WEPP predicted on-field furrow irrigation erosion

The Water Erosion Prediction Project (WEPP) model has the ability to predict erosion from furrow-irrigated fields. A previous evaluation showed that WEPP-predicted infiltration and soil loss correlated poorly with field measurements. Our objective was to further evaluate the WEPP model for furrow irrigation by comparing on-field distribution of measured and predicted infiltration, runoff and soil loss. We used data from three fields with Portneuf silt loam (coarse-silty, mixed, superactive, mesic Durinodic Xeric Haplocalcids) near Kimberly, ID. Single-event WEPP simulations were used so predicted erosion could be evaluated without the effects of daily model adjustments to effective hydraulic conductivity, critical shear and rill erodibility. Single-event simulations showed that the model could only adequately predict infiltration and runoff within a field when effective hydraulic conductivity was calibrated for each irrigation. However even with accurate furrow flows, the WEPP model could not adequately predict sediment detachment, transport, and deposition within a field. Comparing measured and predicted on-field distribution of soil loss indicated that transport capacity was over-predicted by the model because deposition was only predicted when detachment was greatly over-predicted. More thorough investigation of the WEPP model programming and more detailed furrow erosion field data are needed to develop an accurate simulation model for furrow irrigation erosion