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

Irrigation-induced erosion reduces yields and muddies rivers

The Snake River plain in southern Idaho was a desert until ambitious and far-sighted men built dams and canals early in this century. The result was green oases with names like Magic Valley and Treasure Valley. and world famous Idaho Potatoes. Nearly four million acres are now irrigated in southern Idaho producing a wide variety of crops

Evaluating WEPP-predicted infiltration, runoff, and soil erosion for furrow irrigation

The Water Erosion Prediction Project (WEPP) model contains a furrow irrigation component to simulate hydrology and erosion in irrigation furrows. It currently is the only multiple-event furrow erosion simulation model available for public use. However, the furrow irrigation component has not been evaluated yet. Therefore, we evaluated the WEPP model for furrow irrigation by comparing predicted infiltration, runoff, and soil loss with field measurements from three southern Idaho studies on Portneuf silt loam (coarse-silty, mixed, superactive, mesic Durinodic Xeric Haplocalcids). Baseline effective hydraulic conductivity, rill erodibility, and critical shear were calibrated using data measured from the upper quarter of two fields. Calibrated effective hydraulic conductivity was within the range of WEPP-defined values for Portneuf soil. Calibrated rill erodibility of 0.0003 s m-1 was almost two orders of magnitude less than the WEPP-defined value of 0.02 s m- 1 , while calibrated critical shear of 1.2 Pa was about one-third of the WEPP-defined value of 3.5 Pa. Predicted infiltration correlated poorly with measured infiltration for most fields. Regression coefficients for predicted versus measured infiltration ranged from -0.07 to 0.35, indicating that predicted infiltration did not vary with measured infiltration. Predicted soil loss correlated well (R2 = 0.57) with measured soil loss from the upper end of the two fields used to calibrate erodibility parameters. At the field ends however; runoff was underpredicted and soil loss was overpredicted. When runoff was predicted reasonably well for an irrigation, cumulated predicted soil erosion across a field did not match cumulated measured erosion at field quarter segments because transport capacity was overpredicted. Deposition was not predicted unless runoff was greatly under-predicted. The WEPP model cannot be recommended for use with furrow irrigation until erodibility parameters and sediment transport are better defined for irrigation furrows

Unique aspects of modeling irrigation-induced soil erosion

The mechanics of soil erosion from irrigated and rainfed lands are similar. Soil particles are detached, transported and deposited. However, there are some systematic differences between irrigation and rainfall erosion. Electrolyte concentrations in irrigation water, for example, are almost always greater than in rain water. Differences between rainfall and irrigation are more prominent for surface irrigation than for sprinkler irrigation. For instance, rainfall wets the soil before runoff begins, but water initially flows onto dry soil in irrigation furrows. Furthermore, furrow flow rate decreases with distance and increases with time, while the opposite tends to occur with rainfall. For sprinkler systems, travel direction and slope aspect interact, so runoff can flow within the irrigated area or from the irrigated area onto dry or wet soil. Thus, a sprinkler-irrigation erosion model must consider both the rainfall-runoff situation and the furrow flow situation. These differences in soil and water interactions must be considered before computer models can accurately simulate irrigation-induced soil erosion

The importance and challenge of modeling irrigation-induced erosion

Irrigation-induced erosion and rain-induced erosion result from very different systematics. Therefore, both cannot be predicted effectively using the same models. The average two-fold yield and three-fold economic advantage of irrigation over rain-fed agriculture, coupled with the fragility of irrigated land and the strategic importance of irrigation development to meet world agricultural production needs, has raised the urgency for the development of robust, accurate, and precise irrigation-induced erosion models. This paper details the rationale for separate irrigation-induced erosion models, presents essential aspects unique to irrigation that must be accounted for in the models, and summarizes the progress (to date) toward the goal of irrigation-induced erosion model development

Polyacrylamide effects on infiltration in irrigated agriculture

Using polyacrylamide (PAM) following the NRCS conservation practice standard increases infiltration in furrow irrigation. PAM at 10 g in-' (10 ppm) during water advance nearly precludes detachment and transport of soil in furrows. If any sediment is entrained in the flow, it is readily flocculated in the presence of PAM and settles to the furrow-bottom in loose pervious structures. It was hypothesized that depositional surface seals that block pores are reduced or made more permeable with PAM. On Portneuf silt beams (coarse-silty, mixed, superactive, Durinodic Xeric Haplocalcid) furrow irrigation net infiltration increased 15%. Net increases on finer textured soils were generally higher. Furrow streams containing more than 5 g L (5,000 ppm) sediment reduced infiltration and infiltration rate more than fivefold compared to streams of clean water. Tension infiltrometry confirmed that PAM's maintenance of open pores to the furrow surface provides the infiltration increase mechanism. Infiltration rates at 40 and 100 min (1.6 and 3.9 inches) tension in PAM-treated furrows were double the rates of control furrows. Recirculating infiltrometer data showed a 30% infiltration increase with PAM use and infiltration was inversely related to maximum sediment concentration in the flow. Furrow inflow of 45 L min-1 (12 gal min-1 ) with PAM treatment decreased stream advance time 13% while reducing sediment loss 76% compared to untreated 23 L min-1 (6 gal min-1) inflows. Use of PAM in sprinkler irrigation streams reduced runoff 70% and sediment loss 75%, but tension infiltration measurements were inconsistent, suggesting changes in surface-sealing effects with sprinkler application of PAM are transient

Estimation of furrow irrigation sediment loss using an artificial neural network

The area irrigated by furrow irrigation in the U.S. has been steadily decreasing but still represents about 20% of the total irrigated area in the U.S. Furrow irrigation sediment loss is a major water quality issue and a method for estimating sediment loss is needed to quantify the environmental impacts and estimate effectiveness and economic value of conservation practices. Artificial neural network (NN) modeling was applied to furrow irrigation to predict sediment loss as a function of hydraulic and soil conditions. A data set consisting of 1926 furrow evaluations spanning three continents and a wide range of hydraulic and soil conditions was used to train and test a multilayer perceptron feed forward NN model. The final NN model consisted of 16 inputs, 19 hidden nodes in a single hidden layer and 1 output node. Prediction performance of the NN model was model efficiency (ME) = 0.66 for the training data set and ME = 0.80 for the testing data set. The prediction performance for the complete data set of 1926 furrow evaluations was ME= 0.70 with an absolute sediment loss prediction error of less than ±5, ±10, ±20, and ±30 kg per furrow for 35%, 53%, 72% and 85% of the data set values, respectively. The NN model is applicable to predicting sediment loss rates between 1 and 300 kg per furrow for furrow lengths between 30 m and 400 m, slopes between 0.1% and 4%, flow rates between 5 L/min-1 and 75 L/min-1, and silt or sand particle sized fractions between 0.1 and 0.75

Polyacrylamide (PAM) - A one million acre progress report

Water soluble polyacrylamide (PAM) was recognized in the early 1990s as an environmentally safe and highly effective erosion-preventing and infiltration-enhancing chemical, when applied in very dilute concentrations in furrow irrigation water (Lentz et al., 1992; Lentz and Sojka, 1994; McCutchan et al., 1994; Trout et al., 1995; Sojka and Lentz, 1997; Sojka et al., 1998a,b). The mode of action involves surface soil structure stabilization and maintenance of pore continuity. A recommended conservation practice standard was published by NRCS in 1995 (Anonymous, 1995) and is being revised in 1999. It delineates considerations and specifies methodology for. PAM-use. Commercial sales of erosion-preventing PAMs began in 1995. Approximately one million acres were treated in the United States in 1999. Extent of adoption of the practice outside the US is less certain, but interest is growing in several countries and continents. Key aspects of this PAM technology development are presented below

Irrigating with polyacrylamide (PAM) - Nine years and a million acres of experience

Polyacrylamide (PAM) has been available commercially since 1995 for reducing irrigation-induced erosion and enhancing infiltration. The first series of practical field tests was conducted in 1991. PAM used for erosion control is a large water soluble (non-crosslinked) anionic molecule (12-15 megagrams per mole) containing < 0.05% acrylamide monomer. In controlled field studies PAM eliminated, on average, 94% (80-99% range) of sediment loss in field runoff from furrow irrigation, with a typical 15-50% relative infiltration increase on medium to fine textured soils compared to untreated controls. Similar but less dramatic results have been seen with sprinkler irrigation. Under some conditions infiltration is unchanged or can even be slightly reduced, e.g. in sandy soils or where PAM application rates are very high. Results are achieved with per irrigation field application rates of about 1 kg per hectare, for furrow irrigation, and 2 to 4 kg per hectare for sprinkler irrigation. Cost of PAM is $7 to$13 per kg. Seasonal application totals vary from 3 to 7 kg per hectare. Farmer field sediment control has been around 80% of test plot results. Substantial runoff reductions have been documented for nutrients, pesticides, microorganisms, BOD, and weed seed. No adverse effects have been seen for soil microbial populations. Crop yields have not been widely documented, though evidence exists for yield increases related to infiltration improvement. High effectiveness, low cost, and ease of application, compared to traditional conservation measures, has resulted in rapid technology acceptance in the US and internationally. PAM-use for runoff water quality protection is one of the most potent new irrigation environmental technologies in the market place. New uses in construction and dryland erosion control are being developed rapidly. This paper discusses new insights and understanding of PAM-use and potential for future development