摘要:

A statistical dynamic formulation of the vertical water budget at a land‐atmosphere interface is outlined. Physically based dynamic and conservation equations express the infiltration, exfiltration, transpiration, percolation to groundwater and capillary rise from the water table during rainstorms and interstorm periods in terms of independent variables representing the precipitation, potential evapotranspiration, soil and vegetal properties, and water table elevation. Uncertainty is introduced into these equations through the probability density functions of the independent climatic variables and yields derived probability distributions of the dependent water balance elements: surface runoff, evapotranspiration, and groundwater runoff. The mean values of these quantities give a long‐term average water balance which, to the first order, defines the annual water yield and water loss in terms of the annual precipitation and potential evapotranspiration and in terms of physical parameters of the soil, vegetation, climate, and water table. This analytical framework provides physical insight into the dynamic coupling of climate‐soil‐vegetation systems. Details are presented in a series of subsequent

ISSN:0043-1397    

DOI:10.1029/WR014i005p00705

年代:1978

数据来源: WILEY

摘要:

Point precipitation is represented by Poisson arrivals of rectangular intensity pulses that have random depth and duration. By assuming the storm depths to be independent and identically gamma distributed, the cumulative distribution function for normalized annual precipitation is derived in terms of two parameters of the storm sequence, the mean number of storms per year and the order of the gamma distribution. In comparison with long‐term observations in a subhumid and an arid climate it is demonstrated that when working with only 5 years of storm observations this method tends to improve the estimate of the variance of the distribution of the normalized annual values over that obtained by conventional hydrologic methods which utilize only the observed annual total

ISSN:0043-1397    

DOI:10.1029/WR014i005p00713

年代:1978

数据来源: WILEY

摘要:

Natural soil systems are modeled one dimensionally from the surface to a stationary water table by a homogeneous medium defined by three independent parameters. Four varieties of soil moisture movement are analyzed separately, and their effects are linearly superimposed. Infiltration and exfiltration are described by the Philip equation, which assumes the medium to be effectively semiinfinite and the internal soil moisture at the beginning of each storm and interstorm period is assumed to be uniform at its long‐term space‐time average. The exfiltration equation is modified for the presence of natural vegetation through the approximate introduction of a distributed sink representing the moisture extraction by plant roots. Gravitational percolation to groundwater is assumed to be steady throughout the rainy season at a rate determined by the long‐term space‐time average soil moisture. Capillary rise from the water table is assumed to be steady throughout the year and to take place to a dry

ISSN:0043-1397    

DOI:10.1029/WR014i005p00722

年代:1978

数据来源: WILEY

摘要:

The depth of interstorm evapotranspiration from natural surfaces is composed (by proportion to vegetal canopy density) of evaporation from bare soil and transpiration from vegetation. The former is obtained in terms of random variables describing initial soil moisture, time between storms, and potential rate of evapotranspiration from an exfiltration analogy to the Philip infiltration equation modified to incorporate moisture extraction by plant roots. The latter is assumed to occur at the potential rate for natural vegetal systems. In a zeroth‐order approximation the initial soil moisture is fixed at its climatic space and time average whereby using an exponential distribution of time between storms and a constant potential rate of evapotranspiration the expected value of interstorm evapotranspiration is derived. This mean value is used to obtain the annual average point evapotranspiration as a fraction of the potential value and as a function of dimensionless parameters defining the climate‐soil‐vegetation s

ISSN:0043-1397    

DOI:10.1029/WR014i005p00731

年代:1978

数据来源: WILEY

摘要:

The Philip infiltration equation is integrated over the duration of a rainstorm of uniform intensity to give the depth of point surface runoff from such an event on a natural surface in terms of random variables defining the initial soil moisture, the rainfall intensity, and the storm duration. In a zeroth‐order approximation the initial soil moisture is fixed at its climatic space and time average, whereupon by using exponential probability density functions for storm intensity and duration, the probability density function of point storm rainfall excess is derived. This distribution is used to define the annual average depth of point surface runoff and to derive the flood volume frequency relation, both in terms of a set of physically meaningful climate‐soil paramet

ISSN:0043-1397    

DOI:10.1029/WR014i005p00741

年代:1978

数据来源: WILEY

摘要:

Mass conservation is employed to express the natural water balance of climate‐soil‐vegetation systems in terms of the average annual values of precipitation, evapotranspiration, surface runoff, and groundwater runoff as derived from the probability distributions of storm properties and from the physics of the appropriate storm and interstorm soil moisture fluxes. The resulting conservation equation is used to define the dimensionless parameters governing the dynamic similarity of the annual water balance. An asymptotic analysis of this water balance equation yields a set of rational criteria for the classification of climate‐soil‐vegetation systems. Sensitivity with respect to the primary climate, soil, and vegetal parameters demonstrates that qualitative changes in water balance behavior are primarily dependent upon the exfiltration effectiveness of the soil. A natural selection hypothesis is presented which specifies the stable vegetation density and the plant coefficient for a given climate‐soil system in which water and not nutrition or light is

ISSN:0043-1397    

DOI:10.1029/WR014i005p00749

年代:1978

数据来源: WILEY

摘要:

The average annual soil moisture balance, as derived from the mechanics of storm and interstorm soil moisture movement and from the statistics of the climatic variables, is used to define the average annual soil moisture. This soil moisture is used in the equation for average annual yield to give a first‐order approximation of the annual precipitation yield function. This function is used to transform the cumulative distribution function (cdf) of annual precipitation into the cdf of annual yield, and application is made in a subhumid and in an arid climate. The derived yield frequency function is seen to be sensitive to the soil and vegetal properties. Proper selection of these parameters brings close agreement with observed streamflow‐frequency and suggests the model's utility for parameterizing drainage basins with respect to effective average soil and vegetal propert

ISSN:0043-1397    

DOI:10.1029/WR014i005p00765

年代:1978

数据来源: WILEY

摘要:

A finite difference version of the Levenberg‐Marquardt method for nonlinear least squares problems has been extended to include inverse problems in distributed estuarial hydraulic systems. The objective in solving the inverse problems was to establish a numerical simulation procedure for estimating best‐distributed Manning's roughness coefficients from sets of observed tide heights. As an illustration, spatially varying Manning's roughness coefficients for the Upper Delaware River Estuary system were determined for several representative sets of tide height data for the period October 1973 to June 1974. The roughness coefficients were modeled as polynomial functions of distance. Manning's n was thus found generally to vary inversely with distance from the head of tide at Trenton to Wilmington. The spatially distributed tidal‐averaged Reynolds numberRewas used to correlate Manning's n and Darcy‐Weisbach's f. The resultant n‐Rerelationships displayed three distinct hydrodynamic flow regimes characterized as having turbulence. Both n and f were found to be independent ofReforRe>1.52 × 106but inversely related toReforRe<1.2 × 106. Among the numerical techniques used to simulate tidal hydraulic transients it was found that a ‘hopscotch’ finite difference method yielded the best compromise between computational economy and o

ISSN:0043-1397    

DOI:10.1029/WR014i005p00777

年代:1978

数据来源: WILEY

摘要:

A method is given for the separation of the major base flow components in a river hydrograph using simple models. Simplifying assumptions are made which enable the models to be used without rainfall data if necessary, suitable information being deduced from the river hydrograph. Lumped parameter hydrological models are used for the calculations of actual transpiration, soil moisture deficit, and aquifer recharge rates. The base flow components are each identified in terms of a recession time constant, an initial value, and an infiltration contribution. The techniques are applied to the River Severn, for which flow components are separated and then used to illustrate applications to a study of the behavior of conservative water quality determinants.

ISSN:0043-1397    

DOI:10.1029/WR014i005p00791

年代:1978

数据来源: WILEY

摘要:

Three zones of different generations of formation‐fluid flow systems were identified from analyses of the potentiometric surface, hypsographic distribution of fresh water heads, pressure‐depth relations, water table elevations, and dynamic pressure increments observed in five extensive water‐bearing units in a 20,400‐mi2(52,840 km2) geologically mature area in northern Alberta. In each zone, fluids move in gravity‐induced flow systems maintained by cross‐formational energy transfer and subject to past or present boundary conditions. The force fields and associated flow systems in the basal zone of Middle Devonian aquifers were generated by and adjusted to the topography of the Pliocene continental surface. However, subsequent to the erosional exposure of the sub‐Cretaceous unconformity about Pleistocene times, the drainage of the middle zone disrupted the supply of energy from the land surface to the Pliocene flow systems and changed them into slowly decaying relicts of regional fluid dynamics tending toward hydrostatic equilibrium. The same event resulted in the formation of the Pleistocene flow systems of the middle zone which straddles the sub‐Cretaceous unconformity and comprises Paleozoic and basal Cretaceous strata. It is recharged mainly in the area's major hill ranges through the overlying thick succession of Cretaceous clastic rocks which include major aquitards also, and partly through reef ‘chimneys’ from the underlying basal zone. Fluids from the middle zone discharge by ascending cross‐formational flow in the major valleys and also by flow along the bedding planes through the unconformity's outcrops at low elevations beyond the boundaries of the area. These fluids are therefore at relatively low potential, which is adjusted to present boundary conditions. The upper hydrodynamic zone is perched on top of the principal Lower Cretaceous aquitard of the area and includes Cretaceous and Quaternary aquifers. Its flow systems are generated by local differences of the Holocene (present) topography and extend only a few hundred feet in depth. Downward leakage from this zone supplies recharge to the middle hydrodynamic zone. Solution of the diffusion equation for transient fluid potentials suggests a halflife time of approximately 0.7 m.y. for the excess hydraulic heads in the basal zone, indicating pre‐Pleistocene origin for the observed flow distributions in that zone and thus supporting conclusions derived from the steady state patterns of fo

ISSN:0043-1397    

DOI:10.1029/WR014i005p00805

年代:1978

数据来源: WILEY