Showing papers in "Journal of Irrigation and Drainage Engineering-asce in 1999"
TL;DR: In this paper, the first two moments of annual streamflow were compared to readily measured basin and climate characteristics, and the relationship was evaluated by deriving their information content in terms of equivalent record length.
Abstract: Estimates of annual streamflow volumes are needed in many different types of hydrologic studies. Usually a streamgauge is unavailable at the location of interest, hence regional methods that relate streamflow to readily measured geomorphic and climate characteristics provide a practical solution. Hydrologic, geomorphic, and climatic characteristics of 1,553 undeveloped watersheds across the United States are used to develop regional regression equations that relate the first two moments of annual streamflow to readily measured basin and climate characteristics. These relations are summarized for each of 18 major U.S. water resource regions. The relationships are remarkably precise, with adjusted R2 values ranging from 90.2–99.8% and an average value of 96.2% across the continent. The usefulness of these relationships is evaluated by deriving their information content in terms of equivalent record length. These results indicate that regional models of annual streamflow, including runoff maps, are less accu...
228 citations
TL;DR: In this paper, the authors present a review of the existing approaches to evapotranspiration, from Penman to Penman-Monteith, and compare their results with the ones of the Food and Agricultural Organization of the United Nations.
Abstract: Past research on evapotranspiration has provided sound theoretical knowledge and practical applications that have been validated through field measurements. Many different approaches have been used; however, when primary concepts and standard definitions are accepted, it is possible to find reasonable agreement among methods. This paper reviews such approaches, from Penman to Penman-Monteith. The standard concepts of potential evaporation (EP) and equilibrium evaporation (Ee), and the introduction of the climatic resistance (re), provide a better understanding of the role of the climate together with surface and aerodynamic resistances (rs and ra). Therefore, the concept of reference evapotranspiration (ETo), particularly the new one adopted by the Food and Agricultural Organization of the United Nations, can be better understood, as well as its limitations. Crop evapotranspiration (ETc) is related to both ETo and Ee. Crop coefficients (Kc) can be shown to have two components, αo and αc, with Kc = αoαc. T...
194 citations
TL;DR: In this paper, Schuurmans et al. presented a model for the design of water level controllers for irrigation and drainage canals that describes the essential characteristics of the processes relevant for canal control (such as water movements and control structures).
Abstract: Schuurmans et al. (1995a) presented a model for the design of water level controllers for irrigation and drainage canals that describes the essential characteristics of the processes relevant for canal control (such as water movements and control structures). This paper evaluates the accuracy of this model in two ways: (1) by comparing its frequency response with a model based on a finite difference approximation of the linearized St. Venant equations, and (2) by comparing simulation results with data from field experiments. Using these results, we characterize the accuracy of the model and discuss how these results can be taken into account in controller design.
124 citations
TL;DR: In this paper, a simple water level controller for irrigation and drainage canals is proposed; the proposed controller has a master-slave structure where the slaves control the flow rates through the control structures.
Abstract: A simple water level controller for irrigation and drainage canals is proposed; the proposed controller has a master-slave structure where the slaves control the flow rates through the control structures. The master controller consists of PI-based controllers for feedback, and a decoupler and feedforward controller that are based on the inversion of a simple dynamic model of the canal system. The applicability of the controller is demonstrated in field experiments.
114 citations
TL;DR: In this paper, adjustment coefficients for air temperature and dew point temperature measurements at dry weather sites were determined for predicting reference evapotranspirations (ET0) for irrigated conditions.
Abstract: Adjustment coefficients for air temperature and dew point temperature measurements at dry weather sites are determined for predicting reference evapotranspirations (ET0) for irrigated conditions. Seasonal and regional variation in changes in temperature parameters versus the ratio of effective precipitation to ET0 are analyzed. The determined adjustment coefficients are tested for validity using weather data from reference weather stations, and paired reference and dry stations. The effects of adjusting air temperature and dew point temperature for site aridity are analyzed using the FAO Penman-Monteith and the Hargreaves equations. Maximum reductions in ET0 caused by adjustments of temperature data for aridity effects was as high as 25%.
105 citations
TL;DR: In this paper, a new approach to modeling canopy resistance is presented as an alternative to the Food and Agricultural Organization of the United Nations Penman-Monteith method with the constant canopy resistance.
Abstract: A new approach to modeling canopy resistance is presented as an alternative to the Food and Agricultural Organization of the United Nations Penman-Monteith method with the constant canopy resistance. The evapotranspiration (ET) model is based on the “big-leaf” approach and a variable canopy resistance. The model's input requires standard meteorological data as in the Penman-Monteith combination approach. The model was validated using weather and grass lysimeter data measured on an hourly basis at Davis, Calif., and on a daily basis at Policoro, Southern Italy. ET estimates from the model were compared with the results of ET values obtained by the Food and Agricultural Organization of the United Nations Penman-Monteith approach using the constant canopy resistance rc = 70 s m−1. The results showed a very convincing performance of the model for estimating reference ET on both an hourly and daily basis. This work confirms that the canopy resistance depends on climate, and that a variable rc is recommended fo...
101 citations
TL;DR: In this paper, a nonlinear optimization-based multiple-objective management model for sustainable utilization of coastal aquifers is formulated and solved, where the management objectives represent plausible scenarios for planned withdrawal and salinity control.
Abstract: A number of nonlinear optimization-based multiple-objective management models for sustainable utilization of coastal aquifers are formulated and solved. The management objectives represent plausible scenarios for planned withdrawal and salinity control in coastal aquifers. The first multiple-objective management model is developed for spatial and temporal control of aquifer salinity through planed pumping (withdrawal) from locations closest to the ocean boundary. The second multiple-objective management model is useful for maximizing sustainable water withdrawal from the aquifer for beneficial uses, while limiting the maximum salinity in the aquifer. The third multiple-objective management model is developed for maximizing sustainable water withdrawal from the aquifer for beneficial uses and minimizing the total pumping at locations adjacent to the ocean boundary to control the salinity in the aquifer. The nonlinear finite-difference form of the steady-state density-dependent miscible flow and salt transport model for seawater intrusion in coastal aquifers is embedded within the constraints of the management model. The constraint method of generating noninferior solutions is used to solve the multiple-objective management problems. The management models are solved for a hypothetical unconfined coastal aquifer system. The projected augmented Lagrangian method of nonlinear programming is used to solve the resulting large-scale optimization problem. The solution results demonstrate the feasibility of the developed optimization models and also the conflicting nature of the various objectives of coastal aquifer management.
72 citations
TL;DR: In this paper, the effects of seepage on the stability, mobility, and incipient motion of sand-bed particles are investigated, and the concept of pseudo-incipient motion with injection and suction was proposed.
Abstract: Seepage effects on the stability, mobility, and incipient motion of sand-bed particles are experimentally investigated. Seepage through a sand bed in a downward direction (suction) reduces the stability of particles, and it can even initiate their movement. The bed erosion is increased with the increased rates of suction. Whereas the seepage in an upward direction (injection) increases the stability of bed particles, it does not aid initiating their movement. The rate of bed erosion is reduced or even stopped by the increased injection rates, Hydrodynamic conditions leading to the so-called “pseudo-incipient motion” with suction (for the initiation of particles movement that are otherwise at rest under no-seepage conditions), and with injection (for only arresting the particles movement that are otherwise moving initially) are evaluated. The conventional Shields curve cannot be used to predict such pseudo-incipient motion conditions with seepage. The concepts thus developed are useful for a better understanding of the sediment transport mechanics and in the design of stable alluvial channels affected by seepage.
71 citations
TL;DR: In this article, the potential of an optimization approach in improving real-time irrigation water management in systems with complex distribution networks is evaluated through application to the irrigation system in the Lower Ayung River Basin in Bali, Indonesia.
Abstract: This paper presents an evaluation of the potential of an optimization approach in improving real-time irrigation water management in systems with complex distribution networks. The optimization approach is based on quadratic programming. The operational objective is to maximize crop production through appropriate water allocation, while maintaining equity between different irrigation schemes and units within schemes. The approach has been evaluated through application to the irrigation system in the Lower Ayung River Basin in Bali, Indonesia. A simulation model of this irrigation system was available, and it has been possible to measure the effectiveness of the optimization approach by comparing the results of simulation runs incorporating optimization with the results of runs representing existing water allocation practice. The results indicate that the optimization approach does have potential and can significantly improve crop production at the basin scale. This paper presents a preliminary assessment ...
62 citations
TL;DR: In this article, a theoretically based end-depth discharge relationship was obtained for both subcritical and supercritical flow in rectangular, triangular, and trapezoidal channels for each cross-section shape, discharges predicted using the theoretical relationship are compared with the available experimental data.
Abstract: Despite the many theoretical and experimental studies carried out in channels having different cross-section shape, slope, and roughness, the problem of the free overfall as a flow measuring device has not been completely solved, and other experiments are needed. A theoretically based end-depth-discharge relationship is obtained for both subcritical and supercritical flow in rectangular, triangular, and trapezoidal channels. For each cross-section shape, discharges predicted using the theoretical relationship are compared with the available experimental data.
53 citations
TL;DR: A new method for control of unsteady flow in open channels using an iterative approach that utilizes an adjoint sensitivity method to efficiently compute gradient information and permits both scheduled and adaptive flow control to be achieved.
Abstract: A new method for control of unsteady flow in open channels is presented. Control is achieved using an iterative approach, the Broyden, Fletcher, Goldfarb, and Shanno quasi-Newton method that utilizes an adjoint sensitivity method to efficiently compute gradient information. The adjoint equations are derived from the differential form of the full shallow-water equations in one dimension and the resulting sensitivies allow a wide class of flows to be controlled. In addition, the adjoint sensitivity method permits both scheduled and adaptive flow control to be achieved. Application of the method to scheduled flow control is presented.
TL;DR: In this article, a mathematical model is developed that describes water uptake from soil by the roots of transpiring plants, and the model also incorporates a sinusoidal root growth function that takes into account the root growth with time.
Abstract: A mathematical model is developed that describes water uptake from soil by the roots of transpiring plants. Starting from a one-dimensional Richards equation with a root water extraction term, a partial differential equation predicting the moisture content in the soil profile is formulated. There are many expressions in literature that predict water extraction by plant roots, each one of them having its own merits and demerits. This study proposes a simple model with a linear root water extraction term that varies with time. The model also incorporates a sinusoidal root growth function that takes into account the root growth with time. The flow equation is subjected to a boundary condition that signifies the potential evaporation or the applied water (head) during the irrigation application time at the top boundary. The simulated model without the extraction function is validated by comparing the model results with experimental studies predicting soil moisture content for both a homogeneous and a layered medium. A linear root water extraction term is later adopted in the model, and a hypothetical case is simulated to compute the water uptake by plant roots. The comparison in all test cases was found to be reasonably good.
TL;DR: In this paper, the effect of continuous flushing of a sediment-water mixture from the settling basin on its removal efficiency was also studied through analysis of experimental data and a new relationship developed.
Abstract: Experimental investigations have been carried out on the sediment removal efficiency of settling basins. Laboratory data on removal efficiency from the present and earlier studies were first used for checking the accuracy of the existing empirical and analytical methods for determination of the sediment removal efficiency of settling basins. The existing relationships were not found to yield satisfactory results over the whole range of data. Therefore, reanalysis of these data was done and a new relationship developed. The effect of continuous flushing of a sediment-water mixture from the settling basin on its removal efficiency was also studied through analysis of experimental data.
TL;DR: In this article, an analytical model, known as RISK-N, is developed to simulate nitrogen cycling in soils, and nitrate transport and fate in soils and ground water, where the soil is separated into upper-root, lower-root and intermediate-vadose zones, each with uniform properties.
Abstract: An analytical model, known as RISK-N, is developed to simulate nitrogen cycling in soils, and nitrate transport and fate in soils and ground water. The soil is separated into upper-root, lower-root, and intermediate-vadose zones, each with uniform properties. Transport in each soil zone is modeled on the basis of complete mixing. Transport in the aquifer, however, is modeled using a two-dimensional advection-dispersion transport equation. A simulation is made with a hypothetical corn plot, using meteorological, soil, hydrologic, and hydrogeological data for the South Platte River region of northeastern Colorado. Sensitivity analyses are performed on model parameters. This study shows that the RISK-N model is capable of simulating nitrate leaching rates, as well as ground-water concentrations, that are consistent with those obtained by numerical models, while requiring fewer input variables.
TL;DR: In this article, the system hydraulics of recharge basins have been examined through a combination of field and laboratory investigations, and it was found that the surface-clogging layer was susceptible to consolidation and to associated reduction in hydraulic conductivity under seepage forces.
Abstract: Water reuse and ground-water recharge can be used to meet the growing demands for water, particularly in arid regions. Ground-water recharge using fresh water or treated wastewater is most often accomplished by infiltration from surface basins. The water percolates through the unsaturated soil region to an underlying aquifer for storage and future use. In the case of wastewater, additional treatment occurs as the effluent flows through the soil. The system hydraulics of recharge basins have been examined through a combination of field and laboratory investigations. These studies indicate that infiltration rates and soil aquifer treatment of wastewater are influenced by soil type and soil profile characteristics, surface clogging material, pond depth, and wetting/drying cycle times. The surface-clogging layer was found to be susceptible to consolidation and to associated reduction in hydraulic conductivity under seepage forces.
TL;DR: In this paper, the authors developed a dimensional analysis approach to estimate discharge sensitivity to temperature, based on the assumption that temperature affects water viscosity and emitter geometry, and developed a factorial analysis of variance on the observed data with the results presented as coefficients of variation.
Abstract: Working on the assumption that temperature affects water viscosity and emitter geometry, the writers have developed a dimensional analysis approach to the potential pressure-discharge relationship to estimate discharge sensitivity to temperature. Its accuracy was validated by experimental data. Flow rates were measured under controlled conditions on samples of six commercial emitters. Pressures of 100, 150, and 200 kPa were applied. Water temperature was modified alternating heating-cooling temperatures from 20 to 40°C. A factorial analysis of variance was performed on the observed data with the results presented as coefficients of variation. Emitter discharge was found to be insensitive to the alternation of heating-cooling temperatures. Discharge of the helical long-path emitter increased with increasing temperature at a maximum rate of 0.7%/°C. In contrast, it decreased in the vortex emitter at a maximum rate of 0.4%/°C. The dependence of orifice-type emitter discharge on temperature was less significant. Discharge of compensating emitters was affected as much by the operating time of each test as by the time elapsed between consecutive tests, and was not dependent on temperature change.
TL;DR: Two low energy precision application (LEPA) and two spray sprinkler methods (low-elevation spray application and overhead spray) were used to irrigate corn, grain sorghum, and winter wheat in the Southern High Plains.
Abstract: Two low energy precision application (LEPA) sprinkler methods (double-ended socks and bubblers) and two spray sprinkler methods (low-elevation spray application and overhead spray) were used to irrigate corn, grain sorghum, and winter wheat in the Southern High Plains. For full or 100% irrigation, sufficient 25-mm applications were applied to maintain soil water at non-yield-limiting levels determined in earlier research with the three crops. Deficit-irrigated treatments were irrigated on the same days as the control treatment in 25 or 33% increments of the fully irrigated amount. Irrigation water was applied to or above alternate furrows with a three-span lateral move irrigation system. Corn and sorghum were grown on beds and furrows with all furrows diked, and wheat was flat-planted without basin tillage. Grain yields increased significantly with irrigation amount (p ≤ 0.05) for all crops during all years. With full irrigation, grain yields varied little among the sprinkler methods, and yields averaged ...
TL;DR: In this article, a sand tube irrigation (STI) method is proposed to increase the efficiency of drip irrigation systems, which consists of removing a soil core beneath the emitter and filling the void with coarse sand.
Abstract: Surface drip irrigation is an efficient system for delivering water to crops; however, conditions at the soil surface affect evaporation rate and efficiency. A method is proposed, sand tube irrigation (STI), to increase the efficiency of drip irrigation systems. This method is specific to permanent tree crops where soil is not tilled or turned. The STI method consists of removing a soil core beneath the emitter and filling the void with coarse sand. The SWMS_2D model, implemented in a 3D axisymmetric form, was used to simulate infiltration, water redistribution, evaporation from the soil surface, and rise of water inside the sand tube. Model simulations were compared with laboratory measurements determined from a weighing lysimeter. The simulated values of water height inside the sand tube and temporal position of the wetting front in both lateral and upward directions closely matched the experimental measurements. The advancements of the wetting front in the downward direction and evaporation estimates was predicted with less accuracy. Experiments showed that relative to surface drip irrigation, the STI method reduced evaporation by approximately 26% over a 4-day period.
TL;DR: In this article, four forms of the Penman combination equation were compared with measured reference evapotranspiration (ET) data from a clipped grass lawn, and the best agreement with measured data, followed by the FAO-Penman (used with the original Penman wind function) and Penman-Watts-Hancock methods, gave almost identical results.
Abstract: Irrigation schemes in the central clay plains of Sudan represent a major irrigated area in Africa. Annual irrigation requirements may approach 1010/m3. The main irrigation season extends for 9 months (mid-June to mid-March). Off-season irrigation requirements mainly for sugarcane and orchards have to compete with the water supply and hydropower for the usually scarce water resources available in the Blue Nile at this time of the year. Accurate estimates of off-season irrigation requirements become critical for such conditions. A prerequisite for this is to estimate reference evapotranspiration (ET) from meteorological and other data. In this paper four forms of the Penman combination equation were compared with measured ET data from a clipped grass lawn. The Penman-Monteith method gave the best agreement with measured data, followed by the FAO-Penman (used with the original Penman wind function) and Penman-Watts-Hancock methods, which gave almost identical results. The Penman 1963 method was the least sat...
TL;DR: The adjusted factor Ga is a generic friction loss correction factor for pipelines with multiple outlets that reduces to a close approximation of the well-known factor F when the outflow at the downstream end is reduced to zero.
Abstract: The adjusted factor Ga is a generic friction loss correction factor for pipelines with multiple outlets. The adjusted factor Ga can be applied to pipelines with or without outflow at the downstream end. Furthermore, this factor can be applied to a pipeline where the first outlet is at a full outlet spacing or a fractional outlet spacing from the pipeline inlet. When the outflow at the downstream end is reduced to zero, the adjusted factor Ga reduces to the adjusted factor Fa. If the first outlet is positioned one outlet spacing from the pipeline inlet, the factor Ga reduces to G. Finally, if both the outflow is zero and the first outlet is one outlet spacing from the pipeline inlet, the adjusted factor Ga reduces to a close approximation of the well-known factor F. The adjusted factor Ga is a function of the number of outlets along the pipeline, the location of the first outlet from the pipeline inlet, the outflow ratio, and the velocity exponent of the head loss formula.
TL;DR: In this paper, a factor G for pipelines with equally spaced multiple outlets and outflow at the downstream end is derived, which allows the design of segments of pipelines with multiple outlets.
Abstract: A factor G for pipelines with equally spaced multiple outlets and outflow at the downstream end is derived. The proposed factor is a function of the number of outlets along the pipeline and also a function of the friction formula used. Factor G allows head loss in such pipelines to be computed directly provided the first outlet is one outlet spacing distance from the pipeline inlet. Under conditions of zero outflow at the downstream end of the pipeline, factor G reduces to the well-known Christiansen's factor F. Factor G allows the design of segments of pipelines with multiple outlets. It may find application with irrigation engineers in designing sprinkler and trickle irrigation laterals and manifolds with multiple-diameter sizes. It also may be used in trickle line hydraulics in flushing mode.
TL;DR: In this article, an analytical framework was developed to address sensitivity of irrigation offtakes. And the concept of head loss equivalent was introduced to explicitly take into account the hydraulic behavior in the dependent canal downstream of the off-takes, where the perturbation of water depth and the deviation of the setting were considered for analysis.
Abstract: This article is an attempt to develop an analytical framework to address sensitivity of irrigation offtakes. The perturbation of water depth and the deviation of the setting are considered for analysis. Sensitivity of delivery takes into account the impacts of the perturbations on the delivery (to the command area of the offtake). Sensitivity of conveyance assesses the effects on the conveyance discharge of the parent canal. Analytical formulations of six sensitivity indicators are provided. The concept of head loss equivalent is introduced to explicitly take into account the hydraulic behavior in the dependent canal downstream of the offtakes. Hydraulic perturbations are considered either as upstream deviations in the parent canal or downstream perturbations in the dependent canal.
TL;DR: The drainage infrastructure constructed by the Inca at ancient Machu Picchu represents a significant public works achievement as discussed by the authors, and the technical analysis of the drainage works demonstrates that the drainage criteria used were reasonable and the implementation exceptional.
Abstract: The drainage infrastructure constructed by the Inca at ancient Machu Picchu represents a significant public works achievement. The difficult site constraints associated with the nearly 2,000 mm per year of rainfall, steep slopes, landslides, and inaccessibility posed drainage challenges that were met successfully by the Inca. The technical analysis of the Inca drainage works demonstrates that the drainage criteria used were reasonable and the implementation exceptional, and that the Inca were good engineers even though they labored without the benefit of a written language or the use of a wheel. Proof of the Inca success with drainage rests with the fact that Machu Picchu lay in the rainforest for 400 years without failure. There is no better example of successful ancient civil engineering than Machu Picchu. It was built by Native Americans before the arrival of the Spanish Conquistadors, was essentially abandoned in 1540 A.D., and endured for 4 1/2 centuries under a thick rainforest until the 20th centur...
TL;DR: In this article, the authors established analytical relationships between the control of canal water depth, the sensitivity of irrigation delivery structures, and the resulting internal performance at the system level, and derived one system sensitivity indicator for adequacy and efficiency, and two for equity (coefficient of variation and Theil information index).
Abstract: Analytical relationships between the control of canal water depth, the sensitivity of irrigation delivery structures, and the resulting internal performance are established at the system level. One system sensitivity indicator is derived for both adequacy and efficiency, and two for equity (coefficient of variation and Theil information index). The level of precision which reflects the effectiveness in controlling water depth is defined as a permissible variation of water depth at the cross-regulator (± ΔH\dR) about the target. The degree of influence exercised by the cross-regulator on offtakes is accounted for through an influence factor between zero and one. The behavior of three different irrigation systems in Sri Lanka and Pakistan is studied with both analytical system indicators and numerical hydraulic simulations. It shows good agreement for a range of precision between 0.02 and 0.2 m. These global system indicators can be used to define the precision level required to achieve a given performance, to estimate actual performance from recorded precision at regulators, and to diminish the system sensitivity, improving the performance for a given precision. Practical operating policies can be inferred from sensitivity information of irrigation systems without the necessity of a complex irrigation operation model.
TL;DR: In this article, the authors tested the hypothesis that sub-irrigation and inter-cropping will reduce leaching losses from cultivated corn and minimize water pollution, and the effects of three fertilizer application rates (0, 180, and 270 kg N ha\u-¹) on leaching were investigated in the freely drained plots.
Abstract: Nitrate leaching from corn production systems and the subsequent contamination of ground and surface waters is a major environmental problem. In field plots 75 m long by 15 m wide, the writers tested the hypothesis that subirrigation and intercropping will reduce leaching losses from cultivated corn and minimize water pollution. Nitrate leaching under subirrigation at a depth of either 0.7 m or 0.8 m below the soil surface was compared with leaching under free drainage. The cropping systems investigated were corn \I(Zea mays\N L.) monoculture and corn intecropped with annual italian ryegrass \I(Lolium multiflorum\N Lam. \Icv.\N Barmultra). The effects of three fertilizer application rates (0, 180, and 270 kg N ha\u–¹) on leaching were investigated in the freely drained plots. The greatest annual loss of NO\d3-–N in tile drainage water (21.9 kg N ha\u–¹) occurred in freely draining, monocropped plots fertilized with 270 kg N ha\u–¹. Monocropped plots fertilized with 270 kg N ha\u–¹, with subirrigation at 0.7 m depth, resulted in annual nitrate losses into tile draining of 6.6 kg N ha\u–¹, 70% less than under free drainage. Annual soil denitrification rates (60 kg N ha\u–¹) with subirrigation at 0.7 m were about three-fold greater than under free drainage. Intercropping under free drainage resulted in a 50% reduction in tile drainage loss of NO\d3-–N compared with monocropping. Off-season (November 1, 1993,to May 31, 1994) tile drainage losses of NO\d3-–N (7.8 kg N ha\u–¹) from freely draining monocropped plots accounted for 30% of the annual tile drainage losses.
TL;DR: In this article, a semi-empirical equation for cumulative infiltration in a furrow irrigation system was developed using an empirical wetting front advance equation and a volume balance technique, which is based on the concept of volume balance.
Abstract: A semiempirical equation for cumulative infiltration in a furrow irrigation system was developed using an empirical wetting front advance equation and a volume balance technique. This equation was ...
TL;DR: In this paper, the hydraulic diffusivity in terms of the Laplace transform parameter, changes in stream stage, and fluctuations of piezometric level at a point near the stream has been estimated using the Least Squares optimization technique.
Abstract: The Laplace transform of convolution equation, which relates aquifer response to boundary per- turbation, expresses explicitly the hydraulic diffusivity in terms of the Laplace transform parameter, changes in stream stage, and fluctuations of piezometric level at a point near the stream. Hydraulic diffusivity has been estimated using the Laplace transform approach. The diffusivity has also been determined from observed re- sponse of an aquifer and the boundary perturbation using the Marquardt method, a least-squares optimization technique. If the observed data are free from random error, the diffusivity can be estimated accurately using the Laplace transform approach. Unlike the least-squares optimization method, the Laplace transform technique automatically gives less weight to the latter part of the aquifer response and thereby to the random error contained in it. Discrete kernel coefficients have been derived, using which the water level rise in an aquifer that can be predicted for any variation in stream stage.
TL;DR: In this paper, a general solution scheme for determining ground-water levels for channel/ground-water systems with recharge is developed and verified using the Laplace transform method to solve a linearized form of the Boussinesq equation.
Abstract: A general solution scheme for determining ground-water levels for channel/ground-water systems with recharge is developed and verified. The analytical solution uses the Laplace transform method to solve a linearized form of the Boussinesq equation. Unlike other solutions, this scheme allows for both boundaries and sources/sinks to vary as a function of time and space. To verify the analytical scheme, three one-dimensional case studies of flow between two line sources in an unconfined aquifer were explored through a base run and a set of sensitivity analyses. These runs involved comparisons to MODFLOW and changes in the boundary conditions and dimensions. As noted, the flow equations were linearized about a point called the representative flow depth. A value of \ihavg, defined as the average water depth between the initial and steady flow conditions, was used as the representative flow depth. Results of the proposed method matched very well with MODFLOW solutions for all times and locations using an optimal linearization point. In addition, using \ihavg improved the solutions compared to those obtained previously.
TL;DR: In this paper, the authors examined the response of the ASCE task committee on canal automation algorithms to a particular anticipatory open-loop control technique, gate stroking, and showed that the quality of the control degraded as a result of errors in model parameters, particularly in cases where flow through the check gates is submerged.
Abstract: Automated open- and closed-loop control systems can enhance the performance of irrigation delivery systems. This paper examines the response of the canal test cases developed by the ASCE task committee on canal automation algorithms to a particular anticipatory open-loop control technique, gate stroking. The performance of the ideal gate-stroking solution is compared with the performance of an approximate gate-stroking schedule that was generated by imposing practical constraints on the frequency and magnitude of the gate adjustments. Also analyzed were the performance of a nonanticipatory open-loop control scheme and the effect of model parameter uncertainties on the effectiveness of the control. For the test cases, the approximate gate-stroking schedules performed similarly to the ideal schedules. For two of the test cases, delivery performance was similar with and without anticipation, but was substantially different for the other two tests. The quality of the control degraded as a result of errors in model parameters, particularly in cases where flow through the check gates is submerged. Results point out the importance of combining open-and closed-loop control measures to improve the overall effectiveness of the control.
TL;DR: In this paper, the authors evaluated electromigration as a process for concentrating and retaining the nitrates close to the anode in soil subjected to hydraulic flow and found that for a given electrical input, the effect was reduced as the hydraulic flow rate increased.
Abstract: Chemicals applied to agricultural lands inevitably move below the plant root zone and may contaminate the underlying ground-water reservoirs. Laboratory open system soil column experiments were conducted to evaluate electromigration as a process for concentrating and retaining the nitrates close to the anode in soil subjected to hydraulic flow. Electromigration was found to be an effective means for concentrating and retaining nitrate close to the anode in saturated sandy soil at low flow rates. However, for a given electrical input, the effect was reduced as the hydraulic flow rate increased, being indiscernible for higher flow rates.