New furrow flume for high sediment loads

Measurement of water flow in furrows from either irrigation or rainfall is difficult when significant soil erosion occurs. It can be accomplished with flumes that back up flow in the furrow, which for moderate to steeply sloping fields causes only small changes in furrow water depth and thus has little influence on the water flow measurement. However, the ponding of water upstream from a flume can have a significant impact on the movement of sediment down the furrow. In one research study, measured sediment transport through the flume was reduced 40% over that measured in a furrow with only a non– constricting metal form that matched the furrow shape. A new furrow flume has been designed that overcomes the limitations of current v–shaped flumes or trapezoidal EEC flumes that cause significant backwater during furrow irrigation. This new flume has a trapezoidal shape with only a side contraction. It was designed to keep flow velocities high over the full range of flow conditions. This new flume is commercially available and has been working successfully in the field for three seasons

The Current State of Predicting Furrow Irrigation Erosion

There continues to be a need to predict furrow irrigation erosion to estimate on- and off-site impacts of irrigation management. The objective of this paper is to review the current state of furrow erosion prediction technology considering four models: SISL, WEPP, WinSRFR and APEX. SISL is an empirical model for predicting annual soil loss from furrow irrigated fields. SISL could potentially be a useful model if a new method was developed to calculate base soil loss for areas other than southern Idaho where it was developed. The WEPP model uses physically-based equations to predict erosion in irrigation furrows, which are assumed to be the same as rills. Primary difficulties with the WEPP model are defining erodibility parameters for furrow irrigation and over-prediction of transport capacity. WinSRFR provides detailed evaluation of furrow hydraulics and sediment detachment, transport and deposition in an individual furrow during a single irrigation event using similar equations as WEPP. Initial evaluations of WinSRFR are promising and development continues to fully simulate the mix of aggregate sizes found in furrow soil and furrow flow. The APEX model uses empirical relationships to predict soil loss from small watersheds. Preliminary evaluation of the APEX model indicated reasonable correlation with measured soil loss in a 170 ha irrigated watershed. All of these methods require further development and/or evaluation before they can be widely applied to furrow irrigated land. In selecting a predictive tool, it should be noted that an empirical equation may be as good as a physically based equation if we cannot quantify the parameters for the physically based equation

Estimating canal pool resonance with auto tune variation

The Integrator-Delay (ID) model is commonly used to model canal pools which do not exhibit resonance behavior. Simple step tests are often used to estimate ID model parameters; namely, delay time and backwater surface area. These step tests change the canal inflow at the upstream end of the pool and observe water depth variations at the downstream end. Some knowledge of the canal pool characteristics are needed to determine the amount of flow change and its duration. The Auto Tune Variation (ATV) method is one method for determining the duration of these step tests. Pools that are under backwater over their entire length tend to exhibit oscillations due to resonance waves. Binary-Random-Sequence (BRS) tests have been used to determine the resonance frequency of such pools, where step tests with different durations are used. PBRS tests are difficult to implement in practice and may not provide the resonance frequency. The intent of this paper is to demonstrate on a real canal that the ATV method can determine both the resonance frequency and the resonance peak height for canal pools whose water levels oscillate

Sediment and phosphorus transport in irrigation furrows

Sediment and phosphorus (P) in agricultural runoff can impair water quality in streams, lakes, and rivers. We studied the factors affecting P transfer and transport in irrigated furrows in six freshly tilled fallow fields, 110 to 180 m long with 0.007 to 0.012 m m' slopes without the interference of raindrops or sheet flow that occur during natural or simulated rain. The soil on all fields was Portneuf silt loam (coarse-silty, mixed, superactive, mesic Durinodic Xeric Haplocalcids). Flow rate, sediment concentration, and P concentrations were monitored at four, equally spaced locations in each furrow. Flow rate decreased with distance down the furrow as water infiltrated. Sediment concentration varied with distance and time with no set pattern. Total P concentrations related directly to sediment concentrations (r2 = 0.75) because typically >90% of the transported P was particulate P, emphasizing the need to control erosion to reduce P loss. Dissolved reactive phosphorus (DRP) concentrations decreased with time at a specific furrow site but increased with distance down the furrow as contact time with soil and suspended sediment increased. The DRP concentration correlated better with sediment concentration than extractable furrow soil P concentration. However, suspended sediment concentration tended to not affect DRP concentration later in the irrigation (>2 h). These results indicate that the effects of soil P can be overshadowed by differences in flow hydraulics, suspended sediment loads, and non-equilibrium conditions

New furrow flume for high sediment loads

Measurement of water flow in furrows from either irrigation or rainfall is difficult when significant soil erosion occurs. It can be accomplished with flumes that back up flow in the furrow, which for moderate to steeply sloping fields causes only small changes in furrow water depth and thus has little influence on the water flow measurement. However, the ponding of water upstream from a flume can have a significant impact on the movement of sediment down the furrow. In one research study, measured sediment transport through the flume was reduced 40% over that measured in a furrow with only a non– constricting metal form that matched the furrow shape. A new furrow flume has been designed that overcomes the limitations of current v–shaped flumes or trapezoidal EEC flumes that cause significant backwater during furrow irrigation. This new flume has a trapezoidal shape with only a side contraction. It was designed to keep flow velocities high over the full range of flow conditions. This new flume is commercially available and has been working successfully in the field for three seasons