A VOLUME BALANCE SOLUTION FOR WATER FLOW OVER FLAT SOIL SURFACES1

ABSTRACT: This paper presents the development of a mathematical model to compute the advance of water flowing over flat soil surfaces. The solution is of interest to the design and management of irrigation systems, and the model can also be applied to overland flow problems. The hydraulics of water flow during the advance phase is simulated by the Lewis-Milne integral equation. The general solution to this equation is obtained by using the Laplace transform theory. A particular solution was developed, based on series expansions, that uses the modified Kostiakov equation to predict infiltration. The solution is given by a double infinite series that has terms of alternate sign. Results from this model show satisfactory agreement when compared with field data collected by the author.     

水射流技术在牙轮钻头中的应用与研究进展

介绍了喷射钻井井底流场特性、喷嘴射流破岩机理、脉冲射流喷嘴、新型水力流道钻头的研究与应用情况，以及水射流技术在石油钻井用钻头上的应用前景。     

Economic and equity implications of land-use zoning in suburban agriculture

A cash-flow viability model is used to evaluate the impacts of land-use zoning on farm households in New Jersey. Findings suggest that zoning results in increased production expenses, lower efficiency and profitability, and the devaluation of land assets. Cash flow and economic viability are, thus, reduced. Impacts of zoning on farm incomes, off-farm incomes, revenues from land sales, indebtedness, and farm sizes were not statistically significant. The results suggest that the use of land-use zoning statutes to guarantee the existence of agriculture may not be equitable unless transferable development rights or other methods of compensating farmers for their losses are simultaneously implemented.     

STORM RUNOFF CHARACTERISTICS OF GRAZED WATERSHEDS IN EASTERN OREGON1

ABSTRACT: Rainfall and runoff data from 485 storms during the summers of 1979–84 were evaluated to characterize storm runoff volumes (SF) and peak flows (QP) for 13 small watersheds in the Blue Mountains of eastern Oregon and to determine differences among grazing intensities and vegetation types. Storm hydrographs were separated by using watershed-specific baseflow rise rates of 0.002–0.013 cfsm/hr. Median SF and QP were 0.0014 in and 0.43 cfsm, respectively, for all storms. Total storm rainfall (PPT) and initial flow (QI) were important stepwise regression variables in accounting for the variation in SF and peak flow above initial flow (QPI); 30- and 60-mm rainfall intensities and rainfall duration were relatively unimportant. Two classes of vegetation were evaluated: (1) western larch-Douglas-fir (nine watersheds), and (2) other (four watersheds representing fir-spruce, lodgepole pine, mountain meadow, and ponderosa pine). Mean SF and QP did not differ (P=0.05) among vegetation classes but significant differences were apparent in the relation of SF to PPT and QI, and QPI to PPT and QI. As PPT and QI increased, SF and QPI from larch-Douglas-fir watersheds increased at a slower rate than they did from the other watersheds. Four levels of grazing intensity had no effect on storm runoff.     

TWO-DIMENSIONAL DAM-BREAK FLOOD-FLOW ANALYSIS FOR ORANGE COUNTY RESERVOIR1

ABSTRACT: A two-dimensional dam-break model was used to predict the inundated area on an alluvial fan downslope from the Orange County Reservoir. The model is based upon a diffusion form of the continuity and momentum equations for long waves in shallow water, and the governing equation is solved by an explicit numerical scheme. In a comparison with a one-dimensional model, the two-dimensional model predicts a wider inundated area.     

Identification of critical areas on forest lands for control of nonpoint sources of pollution

Most nonpoint source pollution problems on forest lands can be controlled by careful planning and management of specific critical areas. Critical areas include sites with high mass and surface erosion hazards, overland flow areas, and the riparian zone. Some guides for identifying critical areas are presented along with examples of land-use constraints that might be applied.     

KALMAN FILTER ESTIMATION AND PREDICTION OF DAILY STREAM FLOWS: I. REVIEW,ALGORITHM, AND SIMULATION EXPERIMENTS1

An important class of models, frequently used in hydrology for the forecasting of hydrologic variables one or more time periods ahead, or for the generation of synthetic data sequences, is the class of autoregressive(AR) models. As the AR models belong to the family of linear stochastic difference equations, they have both a deterministic and a stochastic component. The stochastic component is often assumed to have a Gaussian distribution. It is well known that hydrologic observations (e.g., stream flows) are heavily affected by noise. To account explicitly for the observation noise, the linear stochastic difference equation is expressed in state variable form and an observation model is introduced. The discrete Kalman filter algorithm can then be used to obtain estimates of the state variable vector. Typically, in hydrologic systems, model parameters, system noise statistics and measurement noise statistics are unknown, and have to be estimated. In this study an adaptive algorithm is discussed which estimates these quantities simultaneously with the state variables. The performance of the algorithm is evaluated by using simulated data.     

GENERALIZED WATERSHED LOADING FUNCTIONS FOR STREAM FLOW NUTRIENTS1

ABSTRACT: Loading functions are proposed as a general model for estimating monthly nitrogen and phosphorus fluxes in stream flow. The functions have a simple mathematical structure, describe a wide range of rural and urban nonpoint sources, and couple surface runoff and ground water discharge. Rural runoff loads are computed from daily runoff and erosion and monthly sediment yield calculations. Urban runoff loads are based on daily nutrient accumulation rates and exponential wash off functions. Ground water discharge is determined by lumped parameter unsaturated and saturated zone soil moisture balances. Default values for model chemical parameters were estimated from literature values. Validation studies over a three-year period for an 850 km² watershed showed that the loading functions explained at least 90 percent of the observed monthly variation in dissolved and total nitrogen and phosphorus fluxes in stream flow. Errors in model predictions of mean monthly fluxes were: dissolved phosphorus - 4 percent; total phosphorus - 2 percent; dissolved nitrogen - 18 percent; and total nitrogen - 28 percent. These results were obtained without model calibration.     

AN EXAMINATION OF RELATIVE PERMEABILITY RELATIONS FOR TWO-PHASE FLOW IN POROUS MEDIA1

ABSTRACT: A key parameter in modeling two-phase flow phenomena is relative permeability. It is important to understand which variables influence relative permeability, especially since so few measurements of relative permeability have been made for typical contaminants at hazardous waste sites. This paper focuses on the effect of five variables on relative permeability: intrinsic permeability, pore-size distribution, viscosity ratio, interfacial tension, and wettability, by critically reviewing previously published relative permeability experiments. The wide variability in the functional relationship between relative permeability and saturation should be considered in attempts to model two-phase flow.     

NONLINEAR SOLUTIONS OF THE BQUSSINESQ EQUATION AND COMPARISONS WITH FIELD OBSERVATIONS1

ABSTRACT: Two models based on variations of the one dimensional Boussinesq equation are presented. The models are formulated by treating each of the two nonlinearities appearing in the equation separately, and the resulting equations are solved by implicit finite difference techniques. The models have been used to predict drawdowns created from large scale pumping at an open coal mine pit dewatering project in Poland. The predictions were found to be in good agreement with data collected over a period of seven years.