Showing papers in "Journal of Hydrologic Engineering in 1999"

Status of Automatic Calibration for Hydrologic Models: Comparison with Multilevel Expert Calibration

Abstract: The usefulness of a hydrologic model depends on how well the model is calibrated. Therefore, the calibration procedure must be conducted carefully to maximize the reliability of the model. In general, manual procedures for calibration can be extremely time-consuming and frustrating, and this has been a major factor inhibiting the widespread use of the more sophisticated and complex hydrologic models. A global optimization algorithm entitled shuffled complex evolution recently was developed that has proved to be consistent, effective, and efficient in locating the globally optimal model parameters of a hydrologic model. In this paper, the capability of the shuffled complex evolution automatic procedure is compared with the interactive multilevel calibration multistage semiautomated method developed for calibration of the Sacramento soil moisture accounting streamflow forecasting model of the U.S. National Weather Service. The results suggest that the state of the art in automatic calibration now can be exp...

Rainfall-Runoff Modeling Using Artificial Neural Networks

Abstract: An Artificial Neural Network (ANN) methodology was employed to forecast daily runoff as a function of daily precipitation, temperature, and snowmelt for the Little Patuxent River watershed in Maryland. The sensitivity of the prediction accuracy to the content and length of training data was investigated. The ANN rainfall-runoff model compared favorably with results obtained using existing techniques including statistical regression and a simple conceptual model. The ANN model provides a more systematic approach, reduces the length of calibration data, and shortens the time spent in calibration of the models. At the same time, it represents an improvement upon the prediction accuracy and flexibility of current methods.

Another Look at SCS-CN Method

Abstract: The Soil Conservation Service-curve number (SCS-CN) method is analytically derived and its basis in the Mockus method analyzed. A modification and a general form of the SCS-CN method are proposed. Using data from five watersheds, the existing SCS-CN method, the proposed modification, and the Mockus method are compared. For these data the modified version is found to be more accurate than the current version.

Coordinate Transformations for Using NEXRAD Data in GIS-Based Hydrologic Modeling

Abstract: Gridded precipitation products created as part of the U.S. National Weather Service's Next Generation Weather Radar (NEXRAD) program are referenced to a national grid called the Hydrologic Rainfall Analysis Project (HRAP) grid, which is used to mosaic precipitation estimates from different radars into a single national precipitation map. The HRAP grid is defined in a polar stereographic map projection that is formed on a plane intersecting a spherical earth datum at 60° N. This paper describes a method for transforming HRAP grid cells into a coordinate system commonly used for mapping geographic information system data sets, quantifies mapping errors associated with using the HRAP coordinate system, and outlines an approach to reduce these mapping errors. The NEXRAD radar rainfall processing software assumes that the earth is spherical rather than using a more accurate ellipsoidal representation. This assumption causes east-west distances to be distorted relative to north-south distances. The magnitude of...

Return Period and Risk of Hydrologic Events. I: Mathematical Formulation

Abstract: The estimation of return periods of hydrological events and the corresponding risks of failure of hydraulic structures that are associated with such events are important aspects in many water resource studies. For simple hydrologic events such as those related to independent annual floods, both the return period and the risk of failure can be readily calculated. However, no general applicable methods are available for the estimation of return periods, risk of failure, and reliability of service in cases of more complex hydrological events such as those related to dependent annual flows and droughts. In this paper, the definitions commonly employed for return period and risk of failure are reexamined and a general procedure for their estimation are presented, which may be applicable to a wide range of hydrological events related to floods, droughts, minimum flows, aquifer levels, and reservoir levels and outflows. Part II of this paper includes numerical examples and applications.

Singapore Rainfall Behavior: Chaotic?

Abstract: The possibility of making short-term prediction of rainfall is studied by investigating the existence of chaotic behavior in the rainfall data series. The minimum number of variables essential and the number of variables sufficient to model the dynamics of the rainfall process are identified. The behavior of rainfall over different record lengths is studied. The effects of the data size and the delay time on the correlation dimension estimate are also analyzed. Daily rainfall data of different record lengths from each of six stations in Singapore are analyzed. The correlation dimension method, the inverse approach of the nonlinear prediction method, and the method of surrogate data (to detect nonlinearity) are used in the analysis. The results indicate that the rainfall data exhibit nonlinear behavior and possibly low-dimensional chaos, which imply that short-term prediction based on nonlinear dynamics might be possible. The minimum number of variables essential is identified as 3 and the number of variab...

Comparing Mean Areal Precipitation Estimates from NEXRAD and Rain Gauge Networks

Abstract: Mean areal precipitation values (MAPX) derived from next generation weather radar (NEXRAD) stage III data are compared with mean areal precipitation (MAP) values derived from a precipitation gauge network. The gauge-derived MAPs are computed using Thiessen polygon weighting, whereas the radar-based MAPXs utilize the gridded stage III radar precipitation products that have been conditioned with gauge measurements and have been merged with overlapping radar fields. We compare over 4,000 pairs of MAPX and MAP estimates over a 3-year time period for each of eight basins in the southern plains reigon of the United States. Over the long term, mean areal estimates derived from NEXRAD generally are 5–10% below gauge-derived estimates. In the smallest basin, the long-term MAPX mean was greater than the MAP. For storm events, a slight tendency for NEXRAD to measure fewer yet more intense intervals of precipitation is identified. Comparison of hydrologic simulations using the two forcings indicates that significant differences in runoff volume can result. This work is aimed at providing insight into the use of a data product that is becoming increasingly available for public use. It also is aimed at investigating the use of radar data in hydrologic models that have been calibrated using gauge-based precipitation estimates.

Long Range Streamflow Forecasting Using El Nino-Southern Oscillation Indicators

Abstract: Hydrologists and water resource planners in the Pacific Northwest region of the United States are under pressure from competing water users to make long-range forecasts of streamflow. At present, long-range streamflow forecasts are not offered. Yet in the Pacific Northwest, a significant lag relationship exists between (El Nino-SouthernOscillation) and streamflow. Using this lag relationship, this study proposes to extend the prediction of spring-summer runoff in the Pacific Northwest from the current 1- to 3-month lead time to a 3- to 7-month lead time. This study looks at the Columbia River basin, where testing is being conducted on a long-range seasonal streamflow forecasting model that uses, as predictors, persistence in streamflow along with two El Nino-SouthernOscillation indicators: the Southern Oscillation Index and the Wright sea surface temperatures. A probabilistic streamflow forecast is made from an optimal linear combination of persistence, Southern Oscillation Index linear discriminant analy...

Definition and Connection of Hydrologic Elements Using Geographic Data

Abstract: Constructing a lumped parameter hydrologic model of a watershed involves dividing the watershed into subbasins and determining their connectivity through the stream network. Subbasin boundaries and stream networks can be described by Geographic Information System (GIS) data layers derived from digital terrain analysis or digitized from maps. By intersecting the subbasin and stream network data layers, then interpreting the resulting geographic features, it is possible to construct automatically a node-arc network description of the watershed comprised of connected hydrologic elements, including subbasins, reaches, junctions, reservoirs, diversions, sources, and sinks of flow to and from the watershed. The procedure, called HEC-PREPRO, has been automated in Arc/Info Arc Macro Language (AML) and ArcView Avenue programs, which produce an ASCII file readable by the Hydrologic Engineering Center’s Hydrologic Modeling System (HEC-HMS). A step-by-step procedure for interpreting geographic data to identify hydrologic elements is presented using a modified version of the Tenkiller Reservoir watershed in Oklahoma as an example. A further example application is presented of the application of HEC-PREPRO to the Upper Mississippi basin and part of the Missouri basin, which results in a hydrologic model containing more than one thousand hydrologic elements.

Return Period and Risk of Hydrologic Events. II: Applications

Abstract: A mathematical formulation to estimate return periods and risks of failure of complex hydrologic events such as those arising from dependent floods and droughts have been examined in the first part of this paper. Specifically, some relationships and algorithms for computing return periods and associated risks for runs arising from independent and dependent events assuming that dependence is represented by a two-state Markov chain have been proposed. The applicability of these procedures is illustrated herein, considering several types of hydrological events with emphasis on those where dependence is important. First, meteorological droughts based on annual precipitation are considered as examples of events consisting of runs in independent trials. Then, minimum streamflows and maximum annual lake outflows are included as examples of dependent events, assuming that dependence is represented by a simple Markov chain. Also, hydrological droughts based on annual streamflow series are considered. In addition, ...

Predicting Infiltration and Ground-Water Mounds for Artificial Recharge

Abstract: Planning systems for the artificial recharge of ground water via surface infiltration requires site investigations to predict infiltration rates and land requirements. Also, the ability of the vadose zone to transmit water to the underlying aquifer must be assessed, and aquifer conditions must be evaluated to predict the rise of ground-water mounds and to determine where ground water must eventually be pumped up again to prevent ground-water mounds below recharge areas from rising too high. A simple technique is presented to convert data from short-duration single-cylinder infiltrometer tests to final infiltration rates for large areas. Also, simple equations are developed to estimate heights of perched ground-water mounds above restricting layers in the vadose zone, to estimate how far from the recharge area ground water must be pumped, and to what depth to create a steady-state system with constant height of the ground-water mound in the recharge area. The procedures are useful for feasibility studies and the preliminary design of recharge projects, including long-term underground storage or water banking.

Halphen Distribution System. I: Mathematical and Statistical Properties

Abstract: In the 1940s, Etienne Halphen, a French statistician and hydrologist, developed a set of distributions for frequency analysis of river flows. Halphen's research was fueled by an extensive practical experience with hydrological data combined with a solid knowledge of statistics. Because of their complex form involving Bessel functions and exponential factorial functions, Halphen's distributions have remained for several years in oblivion. This paper revisits the three types of Halphen distributions, in particular their mathematical and statistical properties. Their flexible shapes and tail properties should make them excellent candidates for frequency analysis of extremes. A companion paper presents procedures for estimating parameters and quantiles of Halphen's distribution.

Tank Model Using Kalman Filter

Abstract: A tank model for rainfall-runoff is used for application of the Kalman filter. The state vector, representing the parameters of the tank model and its initial values, was estimated by trial and error. The tank model using the Kalman filter with a recursive algorithm accurately predicted runoff in a basin in Korea. The filter allowed the model parameters to vary in time and reduced the physical uncertainty of the rainfall-runoff process in the river basin.

Approximate Convection-Diffusion Equations

Abstract: This paper describes the development of simplified momentum equations, in stage as well as in discharge formulations, governing the transition between the diffusion and the kinematic waves (including the latter). It also describes the application of these equations to arrive at the approximate convection-diffusion equations. The appropriateness of these approximate convection-diffusion equations to model flood waves in the transition range is established, and the characteristics of these equations are studied from the point of view of description of the loop-rating curve. The development of these simplified equations provides a theoretical justification for their use in the well-known “Jones formula” expressed as Q/Q0 = {1 + [1/(S0c)]∂y/∂t}1/2 for converting the stage to discharge of a diffusive flood wave—an approach that has hitherto been considered to be logically incorrect.

Regional Flood Formulas for Seven Subzones of Zone 3 of India

Abstract: Regional flood frequency curves are developed by fitting the L-moment based generalized extreme value distribution to annual maximum peak flood data of small-to-medium size catchments of the seven hydrometeorological subzones of Zone 3 and combined Zone 3 of India. These seven subzones cover an area of about 1,041,661 km2. Relationships developed between mean annual peak flood and catchment area are coupled with the respective regional flood frequency curves for derivation of the regional flood formulas. The regional flood frequency curves developed for each subzone together with at-site mean annual peak floods may be used for gauged catchments, whereas for ungauged catchments, regional flood formulas developed for the respective subzones may be adopted for obtaining rational flood frequency estimates.

Modeling Hydrologic and Water Quality Responses to Grass Waterways

Abstract: The impact of vegetation filter strips on runoff, sediment yield, and atrazine loss from a cultivated field was investigated using a physically based, distributed watershed model. The field to which the model is applied has a gentle to flat sloping surface covered by a thin topsoil layer underlain by a claypan and is located in the Goodwater Creek watershed, a USDA research site in central Missouri. The model, which works on a cell basis, was developed to route runoff, sediment, and soluble chemical downslope from one cell to the next. The spatial variability of soil, depth of the topsoil, and vegetation are allowed among cells; each cell, however, is represented as a homogeneous unit. Our investigation indicates that changing waterway cover from natural sparse vegetation to dense grass has great potential for retarding runoff and reducing sediment loss, but it is not effective for controlling atrazine loss on claypan soils.

Halphen Distribution System. II: Parameter and Quantile Estimation

Abstract: In this paper, the second in a series of two, procedures for the estimation of parameters and quantiles of the Halphen type A, B, and IB distributions are presented. Because the Halphen distributions are members of the exponential class of distributions, parameters can be estimated from sufficient statistics, and maximum likelihood estimators should possess certain optimality characteristics. In some cases, the maximum likelihood system of equations does not allow a solution, and the limiting forms of the Halphen distributions, the gamma and inverse gamma, should alternatively be considered. The asymptotic variance of parameter estimators may be obtained by inverting the Fisher information matrix. The asymptotic variance of quantile estimators is obtained by classical first-order approximations. Practical experience with fitting the Halphen distributions is reported.

Geostatistical Applications in Ground-Water Modeling in South-Central Kansas

Abstract: This paper emphasizes the supportive role of geostatistics in applying ground-water models. Field data of 1994 ground-water level, bedrock, and saltwater-freshwater interference elevations in south-central Kansas were collected and analyzed using the geostatistical approach. Ordinary kriging was adopted to estimate initial conditions for ground-water levels and topography of the Permian bedrock at the nodes of a finite difference grid used in a three-dimensional numerical model. Cokriging was used to estimate initial conditions for the saltwater-freshwater interface. An assessment of uncertainties in the estimated data is presented. The kriged and cokriged estimation variances were analyzed to evaluate the adequacy of data employed in the modeling. Although water levels and bedrock elevations are well described by spherical semivariogram models, additional data are required for better cokriging estimation of the interface data. The geostatistically analyzed data were employed in a numerical model of the Siefkes site in the project area. Results indicate that the computed chloride concentrations and ground-water drawdowns reproduced the observed data satisfactorily.

Adaptive Tessellation Method for Creating TINs from GIS Data

Abstract: Terrain models created from triangulated irregular networks (TINs) can be used to delineate watershed and subbasin boundaries. However, an important criterion for accurately defining boundaries is that triangle edges of the TIN honor linear drainage features such as streams, canals, and roads. Typically, this requires a certain amount of labor-intensive, manual editing. A new algorithm has been developed for automatically creating TINs from a set of Geographic Information System (GIS) objects that correspond to the drainage features. The resulting TIN honors all of the drainage features and is well suited to automated basin delineation.

Runoff in Shallow Soils under Laboratory Conditions

Abstract: Laboratory experiments of runoff production in shallow soils were conducted on plots consisting of a bedrock layer, an intermediate soil layer, and a crushed stone cover layer. Artificial rainfall was supplied in varying amounts and time sequences; and surface runoff, soil layer interflow, and throughflow were measured. The purpose of the experiments was to investigate infiltration mechanisms in shallow soils and to characterize the effect of stone cover on the partitioning of rainfall at the soil surface. Two soil types were used: (1) A sandy loam; and (2) a silty clay loam. In the case of the sandy loam, the results showed that the majority of rainfall infiltrated readily into the soil, where it subsequently moved downward to the bedrock as throughflow. Strong throughflow response was attributed to preferential flow through large soil pores. Because these macropores formed naturally during the experiments, this work serves as a plot-scale demonstration of the role of rainfall as a factor of change of so...

Finite-Element Method for Contaminant Transport in Unsaturated Soils

Abstract: A numerical model to simulate miscible contaminant transport through unsaturated soils is presented. To account for the influence of multiple nonequilibrium sources on the contaminant transport, six governing phenomena of the miscible contaminant transport (i.e., convection, mechanical dispersion, molecular diffusion, adsorption, degradation, and immobile water effect) are integrated into the present model. The pollutant volumetric concentration in mobile water is taken as primary unknown, whereas the pollutant concentration in immobile water and the solid particles of soils are treated as state variables at the element integration points. Based on a splitting of the generalized convective operator from the diffusive operator, a modified version of the characteristic Galerkin method is developed to discretize the equations governing the contaminant transport phenomena. A fully explicit algorithm is then derived for the numerical solution of the finite-element equations in time domain. The numerical examples illustrate the performance and the capability of the presented model and algorithms.

Reverse Routing of Flood Hydrographs Using Level Pool Routing

Abstract: In level pool routing, which is the simplest hydrological routing method, the downstream discharge may be expressed explicitly in terms of the inflow and the channel or reservoir characteristics. The level pool routing equation can also be used to estimate the inflow hydrograph given the outflow hydrograph and the water level in the reservoir. Unfortunately, use of the traditional level pool routing method, which is based on the implicit finite difference scheme, for reverse routing has been unsuccessful, despite the simplicity of the problem. If a simple explicit centered differencing scheme is used instead for simulating the inflow hydrograph, the problems associated with traditional schemes, which requ8ire the application of filtering techniques, are bypassed. This is demonstrated using a realistic hypothetical example and a case study. The explicit scheme results are comparable in accuracy with results from the implicit scheme without resorting to the use of filtering techniques. The simple explicit scheme produces a direct solution to the problem and should be the preferred method for both level pool and reverse level pool routing.

Effects of Unsaturated Zone on Ground-Water Mounding

Abstract: The design of infiltration basins used to dispose of treated wastewater or for aquifer recharge often requires estimation of ground-water mounding beneath the basin. However, the effect that the unsaturated zone has on water-table response to basin infiltration often has been overlooked in this estimation. A comparison was made between two methods used to estimate ground-water mounding—an analytical approach that is limited to the saturated zone and a numerical approach that incorporates both the saturated and the unsaturated zones. Results indicate that the error that is introduced by a method that ignores the effects of the unsaturated zone on ground-water mounding increases as the basin-loading period is shortened; as the depth to the water table increases, with increasing subsurface anisotropy; and with the inclusion of fine-textured strata. Additionally, such a method cannot accommodate the dynamic nature of basin infiltration, the finite transmission time of the infiltration front to the water table, or the interception of the basin floor by the capillary fringe.

Treatment of Zeroes in Tail Modeling of Low Flows

Abstract: The presence of zeroes in a record of low flows usually has been interpreted as being indicative of a stream that goes dry during some periods. However, in some instances, zeroes may appear in a gauging record simply because the actual discharge was below a measurement threshold. For example, in some regions it is sometimes true that the lower limit of a stream gauge is above the true stream bottom, and any (censored) discharges not registered by the gauges are recorded as zeroes. This paper presents a comparison of alternative methods for treatment of zeroes in low-flow estimation procedures when tail models are employed for modeling purposes. Simulation experiments indicate that a Weibull tail model, as fitted using a likelihood-based method for inclusion of censored data, is the best estimator of the 10-year low-flow quantile when zeroes in a data set have arisen as a consequence of censoring. When zeroes in a data set exist because the stream is an ephemeral one, a lognormal mixed tail model fitted us...

Comparison of Hurst Exponent Estimates in Hydrometeorological Time Series

Abstract: The Hurst exponent can be estimated by different methods. Two estimation methods are considered in this study. In the first estimate, the rescaled range of a hydrometeorological series is plotted against the lag on a logarithmic scale and the slope of the line fitted by least squares. In the second method, the Hurst exponent is estimated by characterizing the time series by a fractional Gaussian noise (FGN) model, which is a long-memory model. The FGN parameter d, which is related to the Hurst exponent, is estimated by two methods. The Hurst exponent is subsequently estimated using the relationship h = d + 0.5. The Hurst estimate based on the rescaled range is robust and is recommended for use. Estimates based on methods that characterize the hydrologic time series by the FGN model are not robust. Hence, they are not recommended.

Comparison of Precipitation Catch Between Nine Measuring Systems

Abstract: A site was established by the U.S. Department of Agriculture-Agricultural Research Service on the Reynolds Creek Experimental Watershed in southwest Idaho in the fall of 1987 and operated through the spring of 1994, to compare precipitation catch between nine precipitation-measuring systems. This site was established as a part of the World Meteorological Organization’s program to compare current national methods of measuring solid precipitation (snow), so the primary emphasis of this study was the measurement of snowfall. Over seven seasons, four of the systems measured snowfall and total catch, which included snow, mixed snow and rain, and rain events, within 4% of the Wyoming shielded gauge, which had the greatest total catch. These measuring systems were the Alter shielded gauge and the dual-gauge system from United States, the double-fence shielded gauge from Russia, and the Nipher shielded gauge from Canada. The unshielded universal recording gauge that was mounted with its orifice at 3.05 m had the least catch in all precipitation categories, which amounted to 24% less snow, 18% less mixed snow and rain, and 10% less rain than was measured by the Wyoming shielded gauge.

Effect of Input and Parameter Uncertainties in Rainfall-Runoff Simulations

Abstract: The uncertainty or reliability of model simulation results produced by rainfall-runoff models is a function of uncertainties in model parameters, input data, and model structure The present study considers a stochastic instantaneous unit hydrograph (SIUH) model describing the catchment as a single linear reservoir with input and transfer functions treated as random processes Errors in runoff predictions caused by errors in input data and model parameters are analyzed by solving the governing stochastic differential equation (SDE) analytically, thus quantifying—in a general way—the error propagation structure and the relative importance of input errors and parameter errors The result shows that the SIUH parameter variance has a direct bearing on the runoff variance, whereas the error contribution from the effective rainfall variance depends on the parameter mean value and the ratio between effective rainfall and simulated runoff Data from 34 rainstorms are selected to verify the analytical SDE approach The selected events represent varying: (1) rainfall intensity and duration; (2) single/multiple peak events; and (3) catchment initial losses The results from the simulations are compared with observed runoff peaks and flood volumes It is concluded that: (1) the SIUH model is a simple yet robust method, which also gives a good description of the model accuracy; (2) the application of a theoretical SDE to estimate the prediction variance is supported by the statistical analysis of simulated and observed runoff; and (3) the estimation of flood peak variance can improve the design of flood control measures

GEV-PWM Model for Distribution of Minimum Flows

Abstract: Equations for the probability weighted moments (PWMs) of the generalized extreme value (GEV) distribution for minima are derived. The GEV-PWM model and five other models are fitted to the low flow data of 16 streams. The suitability of the models is checked by the probability plot correlation coefficient test. Weibull distribution fits the data better than lognormal. GEV-PWM has the best performance among the three-parameter models, but it frequently leads to infeasible lower bounds. The 10-year minimum flow estimates based on various models are determined. In the majority of cases (11 stations), differences between the largest and the smallest estimates are <20%. However, in a few cases, rather large differences (71%) are found. The estimates from the GEV-PWM and W3-MSO models are usually either the largest or smallest at a station.

Determination of Optimal Loss Rate Parameters and Unit Hydrograph

Abstract: Reduction in deviation between predicted and observed runoff ordinates, and accurate estimation of loss rate parameters, have received considerable attention from many researchers. Linear programming is an optimization tool that is being used to determine the optimal unit hydrograph for a watershed from observed rainfall-runoff data, but requires the rainfall losses a priori. Nonlinear programming models overcome this problem but require good initial values of decision variables. The method presented herein determines the optimal loss rate parameters and unit hydrograph using infiltration theory, unit hydrograph theory, and linear programming. A comparison of the results with previous methods shows the better predictive capability of the model.