Showing papers in "Journal of Irrigation and Drainage Engineering-asce in 1990"
TL;DR: In this article, the concepts developed in the heuristic discussion are developed into a set of rigorous mathematical expressions for determination of optimum water use under deficit irrigation, which can be used to estimate the range of water use within which deficit irrigation would be more profitable than full irrigation.
Abstract: The economics of deficit irrigation are examined. The concepts developed in the heuristic discussion are developed into a set of rigorous mathematical expressions for determination of optimum water use under deficit irrigation. These expressions also can be used to estimate the range of water use within which deficit irrigation would be more profitable than full irrigation. The expressions are completely general in the sense that they can be used with any crop production function and cost function that the analyst chooses. The general expressions are used to derive a set of specific expressions for a particular case study involving a quadratic production function and linear cost function.
368 citations
TL;DR: In this article, the authors developed a set of performance measures for irrigation water delivery systems in terms of adequacy, efficiency, dependability, and equity of water delivery, which can be incorporated in an irrigation system monitoring program and can provide a framework for assessing system improvement alternatives.
Abstract: Performance measures are developed that facilitate analysis of irrigation‐water delivery systems in terms of adequacy, efficiency, dependability, and equity of water delivery. The measures provide a quantitative assessment not only of overall system performance, but also of contributions to performance from the structural and management components of the system. Spatial and temporal distributions of required, scheduled, deliverable, and delivered water are used to calculate the performance measures. These variables may be estimated by a combination of field‐measurement and simulation techniques. The performance measures can be incorporated in an irrigation‐system monitoring program and can provide a framework for assessing system improvement alternatives. They are amenable to decomposition analysis of systems, allowing assessment of trends in performance among distinctly defined subregions or comparison of performance at different levels of system‐network hierarchy. Example applications to systems typical...
321 citations
TL;DR: Carbofuran, alachlor, atrazine, bromide (a tracer), and nitrate are applied to two tile-drained plots of com, one of which is conventionally tilled and another that is no-till.
Abstract: Carbofuran, alachlor, atrazine, bromide (a tracer), and nitrate are applied to two tile‐drained plots of com, one of which is conventionally tilled and another that is no‐till. Soil water samples are collected from the plots with suction lysimeters and ground‐water samples are collected from wells and tile drains. The no‐till plot first showed low concentrations of atrazine and alachlor ranging from 0.1 to 0.4 μg/L below the root zone one month after application, but the conventionally tilled plot showed no pesticides below the root zone until late fall, when atrazine was detected at 0.4 μg/L. Dye studies indicated that, in the no‐till plots, some of the pesticide bypasses the root zone through surface‐connected ma‐cropores, whereas in the conventionally tilled plot, most of the pesticide is adsorbed within the root zone as a result of greater contact with the soil. Concentrations of bromide (which is not adsorbed) in samples collected from wells and suction lysimeters do not differ between the two plots....
89 citations
TL;DR: A computationally efficient algorithm that can be implemented in a microcomputer is developed to solve the complex problem of irrigation management in a large heterogeneous basin by using a multilevel optimization technique.
Abstract: The complex problem of irrigation management in a large heterogeneous basin is solved by using a multilevel optimization technique. The real problem consists of determining the optimal cropping patterns in various subareas of the basin, the optimal design capacities of irrigation facilities including both the surface and ground water resources, and the optimal water allocation policies for the conjunctive use. The objective of such a management is to obtain a high level of economic efficiency in the irrigation development and water use system within a hydrologically feasible policy domain. Various alternative activities, such as surface water diversion and pumpage, ground water withdrawal and recharge, and alternative future operational scenarios, have to be analyzed in an integrated way. The solution strategy is based on the physical decomposition of a large system into interconnected subsystems. A computationally efficient algorithm that can be implemented in a microcomputer is developed to solve the mu...
84 citations
TL;DR: In this paper, a general infiltration model is derived using a systems approach using a first-order analysis is performed to quantify the uncertainty involved with the generalized model, and a solution of the Holtan model has not been reported in the literature.
Abstract: A general infiltration model is derived using a systems approach The models of Horton, Kostiakov, Overton, Green and Ampt, and Philip are some of the example models that are shown as special cases of the general model An equivalence between the Green‐Ampt model and the Philip two‐term model is shown The general model also provides a solution for the Holtan model expressing infiltration as a function of time This solution of the Holtan model has not been reported in the literature A first‐order analysis is performed to quantify the uncertainty involved with the generalized model The general infiltration model contains five parameters Two of the parameters are physically based and can therefore be estimated from the knowledge of soil properties, antecedent soil moisture conditions, and infiltration measurements; the remaining three can be determined using the least squares method The model is verified using ten observed infiltration data sets Agreement between observed and computed infiltration is
78 citations
TL;DR: In this article, the Blasius equation is combined with the Darcy-Weisbach equation to give a simple and accurate equation written in terms of flow rate, pipe length, and pipe diameter.
Abstract: The Blasius equation which has been verified by many researchers and has been recently shown to work very well for small diameter plastic pipe can be combined with the Darcy-Weisbach equation to give a simple and accurate equation written in terms of flow rate, pipe length, and pipe diameter. It allows for correcting for viscosity changes, and is very accurate for flows resulting in Reynolds numbers less than 100,000. Unlike other commonly used empirical equations in a similar form, this equation is theoretically sound and dimensionally homogeneous.
75 citations
TL;DR: In this article, a review of existing predictive and non-predictive parameter estimation methods is presented with a formulation of the inverse surface irrigation problem, and the search of the parameter set that minimizes the errors between field observations and the linearized zero-inertia model is performed.
Abstract: The basic concepts and procedures for the estimation of roughness and infiltration parameters encountered in surface irrigation are presented. A review of existing predictive and nonpredictive parameter-estimation methods is presented with a formulation of the inverse surface irrigation problem. Conjugate gradient and variable metric techniques are used for the search of the parameter set that minimizes the errors between field observations and the linearized zero-inertia model. Appropriate constraints that restrict the variation of parameters within physically realistic limits are also imposed on the objective function. The performance and radius of convergence of the search algorithm are studied by numerical tests that demonstrate the steps in the development of the associated objective function and the strategy required for convergence to the correct values of the field parameters. It is concluded that a key role is played by the formulation of the direct problem and its numerical solution, and that the nonlinear field-parameter search converges quickly when the influence of independent parameters can be decoupled during construction of the objective function.
64 citations
TL;DR: In this paper, the best estimates of effective rainfall have been proposed in the past, including: direct measurement techniques; empirical methods; and soil water balance methods; however, none of these methods have been used in this paper.
Abstract: Numerous methods for estimating effective rainfall have been proposed in the past, including: direct measurement techniques; empirical methods; and soil water balance methods. The best estimates of...
59 citations
TL;DR: There are three main types of conjunctive use projects: stream diversions, dam and reservoir only, and total system as discussed by the authors, which can usually increase yields at lower costs than more dams and reservoirs operated separately.
Abstract: Conjunctive use of surface water and ground water can usually increase yields at lower costs than more dams and reservoirs operated separately. There are three main types of conjunctive use projects: (1) Stream diversions; (2) dam and reservoir only; and (3) total system. There are many advangates of ground‐water storage compared with surface storage, and of conjunctive use compared to independent use. Physical, operational, financial, and institutional constraints may be encountered by the project proponents. Institutional issues may be the most difficult to resolve. Often, several governmental agencies may provide funds and have responsibilities for various features of conjunctive‐use projects. Implementation is more difficult in countries where surface‐water development has historically dominated water‐supply project formulation. Court decisions in California have provided guidelines for conjunctive‐use programs, especially in defining the rights of public agencies. Four areas in California that have e...
51 citations
TL;DR: In this paper, an analysis to determine infiltration parameters from the early stages of furrow advance is reported, using a kinematic-wave simulation model in conjunction with a simplex search procedure to minimize the differences between measured and predicted advance rates.
Abstract: An analysis to determine infiltration parameters from the early stages of furrow advance is reported. The analysis uses a kinematic-wave simulation model in conjunction with a simplex search procedure to minimize the differences between measured and predicted advance rates. The technique uses a variable and expanding data set to forecast advance times and is therefore a useful prelude to real-time feed back control systems for the future automation of furrow irrigation systems. Results from four furrow evaluations involving a sandy loam and a silty clay loam are given to demonstrate the capability of the analysis. The analysis was first verified by using the complete advance data sets for the evaluations. The analysis yielded the same values of the three Kostiakov-Lewis infiltration parameters found in independent field measurement. In a second investigation, the basic intake-rate parameter in the Kostiakov-Lewis function was fixed and the analysis was repeated with advance data from the early stages of advance to determine if and how soon the analysis would estimate reasonably accurate values of the other two infiltration parameters. The results indicate that infiltration parameters can be estimated with sufficient accuracy from early advance data to allow an accurate forecast of efficiency and uniformity at the end of the irrigation.
49 citations
TL;DR: In this paper, a basis for comprehensive analytical models, equations, and their solutions for border or furrow irrigation advance is derived, which consists of an analytical solution of the zero-inertia (ZI) differential equations, which assumes a moving momentum representative cross section in the water body.
Abstract: A basis for comprehensive analytical models, equations, and their solutions for border or furrow irrigation advance is derived. This basis consists of an analytical solution of the zero-inertia (ZI) differential equations, which assumes a moving momentum representative cross section in the water body. It takes into account the time-varying character of infiltration and does not contain any restrictions on the infiltration formula used. Subsequently, this solution is specifically developed for a zero-inertia model of border irrigation advance (ZIMBA). It proved efficient in three types of application: (1) Simulation of irrigation advance in sloping borders; (2) replacing within a numerical model the cumbersome, but widely used mass-balance techniques for calculating the flow in the tip region of the wave; and (3) generating initial values for starting a numerical simulation of border irrigation. The results of ZIMBA are compared to observed values and to results of a full hydrodynamic model. For the data analyzed here, the prediction error always remains below 4%.
TL;DR: In this article, Atrazine and metolachlor are applied preemergent to corn in plots that are either drained 10cm plastic tubes 1m deep or undrained, respectively.
Abstract: Atrazine and metolachlor are applied preemergent to corn in plots that are either drained 10cm plastic tubes 1m deep or undrained. Herbicide concentrations in the soil profile down to 30 cm and in ...
TL;DR: In this article, the authors provide specific examples of deficit irrigation practices in the Columbia Basin with the aim of developing better understanding of the practice and economic merits of this irrigation-management technique.
Abstract: A companion paper demonstrates that deficit irrigation can be profitable when irrigation costs are high or water supplies are limited. The present paper provides specific examples of deficit irrigation practices in the Columbia Basin with the aim of developing better understanding of the practice and economic merits of this irrigation-management technique. The fundamental concepts developed in the companion paper are illustrated with data from nine cooperating farms. The economic analyses account for all costs of production, including the following: (1) Variable costs of irrigation; (2) variable costs not directly associated with irrigation operations; and (3) capital and other fixed costs of production. The second and third cost categories were of greater importance to the analysis than were the direct costs of irrigation. Estimates of average 10-year incomes were derived from farm data. Based on these estimates, farms that were practicing deficit irrigation achieved lower net incomes per hectare but higher net incomes per unit of applied water than the fully irrigated farms. This suggests that their irrigation practices were nonoptimal, but that they were benefiting financially from deficit irrigation.
TL;DR: In this article, a desktop method is presented to analyze or size detention ponds and outlet facilities, based on the usual reservoir-routing technique that couples the hydrologic storage equation with an expression describing the flow through the outlet structure.
Abstract: A desktop method is presented to analyze or size detention ponds and outlet facilities. Different initial conditions are allowed. When used for design purposes, the method determines the size of the outlet facility for a given pond. However, if the pond is inadequate to meet the design criteria set, the method determines the required stage‐storage relationship. The method is based on the usual reservoir‐routing technique that couples the hydrologic‐storage equation with an expression describing the flow through the outlet structure. The equations are rearranged in terms of several dimensionless parameters. A computer model is used to solve the governing equation using a finite difference scheme. The numerical results obtained in terms of systematically chosen combinations of the governing dimensionless parameters are generalized based on the concept of similarity. The generalized results are presented in chart form. Sample applications of these charts are illustrated.
TL;DR: In this article, the shooting or initial value method started from the downstream end and proceeded upstream against the flushing or initialvalue method, and the shooting method was used to obtain subcritical conditions in surface irrigation.
Abstract: Flow in surface irrigation is subcritical and downstream conditions can propagate upstream. The shooting or initialvalue method started from the downstream end and proceeded upstream against the fl...
TL;DR: In this paper, a local optimal control technique control of an individual gate for operation of an irrigation canal with a single reach is presented, by using the concepts of control theory, an expression for an expression that describes the optimal control of a gate.
Abstract: This paper presents a local optimal control technique control of an individual gate for operation of an irrigation canal with a single reach. By using the concepts of control theory, an expression ...
TL;DR: In this article, the authors point out the need for monitoring and evaluation of irrigation projects, outlines the main requirements for a functional system, and provides a realistic framework for carrying it out, and proposes a new evaluative minnd-set that enables managers to assess their projects' performance objectively, reflect on what has been learned for future use, and adjust policies on the basis of that knowledge whenever necessary.
Abstract: Monitoring and evaluation of irrigation projects has been a neglected subject, but must play a more important role in the future if the irrigation management process is to be improved. Theprocess is complex, since a large number of regular, specific tasks must be performed, both concurrently and sequentially, and coordinated by a variety of professionals within available time and resource constraints. The paper points out the need for monitoring and evaluation, outlines the main requirements for a functional system, and provides a realistic framework for carrying it out. For any evaluation to be used, it must be credible—objective, accurate, and fair. Reports should be clear, unambiguous, balanced in terms of strengths and weaknesses, and contain justifiable conclusions and recommendations. For monitoring and evaluation to succeed, irrigation managers need to develop a new evaluative minnd-set that enables them to appraise their projects’ performance objectively, reflect on what has been learned for future use, and adjust policies on the basis of that knowledge whenever necessary.
TL;DR: In this article, the authors defined droughts using daily streamflow series and different truncation levels including 30, 50, 60, 70, 80, and 90% of recorded daily flows.
Abstract: Droughts are defined using daily streamflow series and different truncation levels including 30%, 50%, 60%, 70%, 80%, and 90% of recorded daily flows. Flow ratios, which are obtained by dividing subbasin flows of different truncation levels by their corresponding outlet flows, are calculated. It is found that the flow ratios of 17 selected subbasins decrease significantly with increasing truncation levels while their mean‐flow ratios are approximately equal to their corresponding area ratios. Therefore, the estimation of irrigation water using the drainage area ratio, which has been practiced in the studied drainage basin, is impractical in case of droughts. Furthermore, assuming the time‐dependent Poissonian behavior of drought series, the drought intensity function was developed to investigate drought severity in the basin. Based on plots of drought intensity function, it is found that the drought intensity has been increasing significantly for the basin investigated.
TL;DR: In this paper, a composite model predicts the consequences on the geography of U.S. irrigation, with the greatest impact of a warmer climate on the agricultural economy in the Western states.
Abstract: Warming of the global atmosphere by 2°‐5° C, and regional changes in precipitation by mid 21st century as greenhouse gases double, is expected. A composite model predicts the consequences on the geography of U.S. irrigation. Percentages of cultivated area irrigated are projected for each state. Predictions of actual area irrigated, which will depend on economic conditions and availability of new water supplies are not made. In all cases percentages irrigated rise, with the greatest impact of a warmer climate on the agricultural economy in the Western states. In the Western states this will occur because of decreases in total area cultivated due to a loss of rainfall agriculture. In the East, irrigation will increase, accompanied by some decrease in cultivated areas. Improved use of technologies could help meet increasing evapotranspiration needs, but large new surface supplies will generally be required to maintain or increase present levels of irrigation.
TL;DR: In this article, the GLEAMS (ground water loading effects of agricultural management systems) model was modified to simulate the generation and degradation of pesticide metabolites and the translocation of the metabolites within and through the root zone is considered.
Abstract: The GLEAMS (ground water loading effects of agricultural management systems) model was modified to simulate the generation and degradation of pesticide metabolites. Translocation of the metabolites within and through the root zone is considered. Translocation of the metabolites within and through the root zone is considered. The modifications have been verified and preliminary validation has been made using field data. The paper presents the model concepts for metabolite generation and degradation. Results of model simulations for fenamiphos metabolite concentrations in the root zone are compared with observed concentrations from a research location in the Georgia coastal plain. These additions to GLEAMS will be helpful to model users working with those nonvolatile pesticides that have toxic metabolites with mobility and persistence characteristics differing from those of the parent compounds. Soil samples are taken periodically during the cropping season at depths corresponding to the GLEAMS model computational layers. The samples are analyzed for fenamiphos and its metabolites for comparison with model simulations. Field observations of metabolite mobility and persistence are compared with limited data in published literature.
TL;DR: Partial irrigation is supplying less water than a crop needs for full protection to stretch water supplies and increase total crop production and profit and partial irrigation principles must be used to understand and direct conventional water conservation programs.
Abstract: Partial irrigation is supplying less water than a crop needs for full protection. Partially irrigating crops is intended to stretch water supplies and increase total crop production and profit. Pakistan is short of water and so partial irrigation is widely practiced. Selecting crop varieties or determining proper irrigation schedules requires applying partial irrigation principles. Only a small part of the irrigation research done in Pakistan considers the effects of partially irrigating crops. All the reviewed mathematical models used to optimize irrigation avoided nonnumerical aspects of irrigation management. These simplifications tend to ignore some costs while fully accounting for all benefits, resulting in poor model performance when compared to actual system management. The most effective actions to implement partial irrigation are improving system reliability, developing and disseminating simple water management rules, and continuing current programs to improve watercourses and level fields. While a sophisticated partial irrigation scheduling program would be difficult technically, socially, and logistically, partial irrigation principles must be used to understand and direct conventional water conservation programs.
TL;DR: In this paper, a method is presented by which the proportions of a watershed that contribute surface runoff in different storms and at different times during the same storm can be determined by analysis of rainfall and runoff records.
Abstract: A method is presented by which the proportions of a watershed that contribute surface runoff in different storms and at different times during the same storm can be determined by analysis of rainfall and runoff records. The method is a modification of a method described in an earlier paper, which eliminates the need for subjective selection of particular runoff events for analysis. The method is illustrated using data from a 16.8‐ha watershed in Queensland, Australia, and the estimates of runoff from the different source areas are compared with actual records of runoff from the whole watershed. Runoff occurred from the entire watershed area on only three occasions in the 15‐yr study period, about 10% of runoff events. In about two‐thirds of runoff events, runoff came only from the 15% of the watershed that has the smallest surface storage capacity.
TL;DR: In this article, the conditions of observability and field parameter identifiability for surface irrigation advance are examined by analytical' techniques and the linearized zero-inertia model and the existence and uniqueness of the inverse irrigation problem are established by numerical tests based on a nonlinear estimation algorithm.
Abstract: The conditions of observability and field‐parameter identifiability for surface irrigation advance are examined by analytical' techniques and the linearized zero‐inertia model. The existence and uniqueness of the inverse irrigation problem are established by numerical tests based on a nonlinear estimation algorithm. The limitations are examined for determining the field parameters of intake and surface resistance from, field‐measured values of advance and depth for border‐strip irrigation. The linearized zero‐inertia model proves to be conditionally observable, and the resistance and two infiltration parameters cannot be identified from measurements of the rate of advance alone. All three parameters on the other hand can be identified from measurements of the surface‐water profile. The design of appropriate experiments that lead to observability of the problem is examined and the analytical and numerical limitations of the zero‐inertia model that hinder the inverse solution of surface irrigation advance a...
TL;DR: The storage coefficient and transmissivity are important aquifer parameters that are useful in assessing the groundwater potential of an aquifer for a non-leaky confined aquifer as mentioned in this paper.
Abstract: The storage coefficient and transmissivity are important aquifer parameters that are useful in assessing the groundwater potential of an aquifer. For a nonleaky confined aquifer, these parameters c...
TL;DR: In this article, an analytical model is developed to simulate all phases of furrow irrigation, and the model transforms any real furrow cross section shape to a discharge-equivalent semicircular shape, and can therefore be applied to any form of Furrow cross-section.
Abstract: An analytical model is developed to simulate all phases of furrow irrigation. The model transforms any real furrow cross section shape to a discharge-equivalent semicircular shape, and can therefore be applied to any form of furrow cross section. Parabolic shapes are used to describe the surface and subsurface flow profiles and their coefficients are determined from the conditions in the gradually varied flow region, rather than in the region of rapidly varied flow at the advance front. Infiltration is simulated in three dimensions rather than in one or two dimensions. The recession phases are simulated by modifying Strelkoff’s model such that the time-varying rate of infiltration is taken into account. One observed data set is used to calibrate the model, and six observed data sets are used to verify it. The model is simple, accurate (less than 8% deviation for all phases), and easy to apply.
TL;DR: In this article, a 3.62 cm Parshall flume is installed in a channel and flow rates are measured with lateral flume crest slopes of 0, 3.6, 6.5, 9.0, 13.2, and 11.8%.
Abstract: A 3‐in. (7.62‐cm) Parshall flume is installed in a channel and flow rates are measured with lateral flume crest slopes of 0, 3.6, 6.5, 9.0, 13.3, -3.8, -4.8, -7.2, and -11.8%. The apparent discharge is compared to the measured discharge for each slope with free outfall conditions. The results indicate that the Parshall flume accuracy is in error approximately 7% at a lateral slope of ±10%. It is determined that the flow measurement requires a 0.75% adjustment for each 1% of lateral settlement at the flume crest. A method for correcting the apparent discharge with the measured discharge is presented for variable lateral slope conditions.
TL;DR: In this article, soil samples were taken from the surface to a depth of 152 cm on 16 irrigated sites and one forested site in the fall of 1983 and spring of 1984 from irrigated corn plots where poultry manure and ammonium nitrate fertilizer were applied at a rate of 202 kg/ha of available nitrogen.
Abstract: Soil samples were taken from the surface to a depth of 152 cm on 16 irrigated sites and one forested site in the fall of 1983. All but one of the irrigation sites had corn grown on it in four out of the previous five years. Soil types of the irrigated sites were Matapeake silt loam, Sassafras sandy loam, Woodstown sandy loam, Rumford loamy sand, and Evesboro loamy sand. Soil samples were also taken in the fall of 1983 and spring of 1984 from irrigated corn plots where poultry manure and ammonium nitrate fertilizer were applied at a rate of 202 kg/ha of available nitrogen. Nitrate concentrations were lower on the forested site than any of the cropland sites. Nitrate leaching was occurring to some extent on all of the irrigated corn sites. The greatest nitrate concentrations in the soil profile occurred where excessive nitrogen was applied using manure in addition to commercial fertilizer. The site where soybeans had been grown in the previous four growing seasons had lower nitrate concentrations than any o...
TL;DR: In this article, a nonlinear optimization model for the design and management of drip irrigation systems is developed, where decision variables are: pipe diameter, pipe length, number of emitters in each lateral and number of laterals in a manifold.
Abstract: This paper develops a nonlinear optimization model for the design and management of drip irrigation systems. Decision variables are: pipe diameter, pipe length, number of emitters in each lateral, number of laterals in a manifold, total number of subunits, number of subunits operating simultaneously, irrigation time per set, and emitter discharge. The model is solved using the GAMS‐MINOS package. To illustrate the capability of the model, an orchard field of pears is selected. The price effect on the results of the model shows that the cost of the system and its operation are relatively small compared with the benefit obtained. The model shows that the results do not yield the minimum cost of the system when the marginal benefit is greater than the marginal cost.
TL;DR: In this paper, the leaching potential of ground water by nitrogen leached from fertilizer on irrigated soils is related to the quantity of nitrateN (NO3-•N) present.
Abstract: Contamination of ground water by nitrogen leached from fertilizer on irrigated soils is related to the quantity of nitrateN (NO3-‐N) present, the leaching potential based on soil texture and percen...
TL;DR: In this paper, Harmonic analysis is used to derive the effect of non-uniform irrigation on deep percolation, and the theoretical study provides an analytical tool with which to evaluate the hydrological significance of irrigation uniformity.
Abstract: This study analyzes factors affecting deep percolation. Harmonic analysis is used to derive the effect of nonuniform irrigation on deep percolation. The Christiansen uniformity coefficient (CUC) is described by a sinusoidal function. It is shown to be proportional to the relative amplitude, the ratio between the amplitude (δ\N\II\N) and mean water application (\II¯\N) of a sinusoidal wave. The amplitude is subject to smoothing by plant root systems of various sizes. A distinction is made between effective uniformity and observed uniformity. The theoretical study provides an analytical tool with which to evaluate the hydrological significance of irrigation uniformity. Deep percolation was shown to be affected by several factors. First is the difference between \II¯\N and the crops’ water consumption. The greater the difference, the greater the amount of deep percolation. Of secondary importance is CUC. For any given amount of water, the amount that percolates below the root zone increases as CUC decreases. Smoothing of water distribution within the soil profile reduces percolation. This effect is more pronounced for a short rather than long distance between nozzles.