摘要:

Size of annual peak flow in a small watershed in western Oregon was reduced 32%, and average delay of all peak flows was nearly 9 hours following clearcut logging. Size of annual peak flows caused by rain with snowmelt was reduced 36%, and peak flows resulting from rain with snowmelt were delayed an average of nearly 12 hours following logging. Changes are attributed mainly to differences in short‐term accumulation and melting of snow. No significant changes were detected in size or timing of peak flows that resulted from rainfall alon

ISSN:0043-1397    

DOI:10.1029/WR015i001p00090

年代:1979

数据来源: WILEY

摘要:

Regression equations are presented for predicting parameters in the geomorphic equations that relate Streamflow discharge at a site to channel width and cross‐sectional area (from which velocity and hydraulic depth can be determined). Two measures are used in these regression equations, drainage area and channel slope, both of which are obtained from topographic maps. Regeneration and simulation tests at stream gage sites located in the Cumberland Plateau Physiographic Province indicate that at higher flows this system of equations can predict width and area within ∼25% about ⅔ of the time. These results appear to be comparable with or better than results that would normally be obtained from the reconnaissance field surveys normally used in Streamflow routing for planning‐level appli

ISSN:0043-1397    

DOI:10.1029/WR015i001p00095

年代:1979

数据来源: WILEY

摘要:

The thermodynamic basis of entropy concepts as applied in fluvial geomorphology is examined closely. It is shown that the principle of minimum entropy production rate and the principle that the most probable state of a system is that which corresponds to a maximum of entropy are not applicable in stream situations. It is concluded that the use of entropy as an approach to stream behavior and sediment transport is of dubious validity.

ISSN:0043-1397    

DOI:10.1029/WR015i001p00103

年代:1979

数据来源: WILEY

摘要:

MostpFcurves are shaped as cumulative distribution functions. From this observation, restricted to nonshrinking or swelling soils, a close relationship is established between the moisture characteristic and the pore size distribution, based on an empirical law relating the pore suction to a characteristic size referred to as the effective pore radius. For many soils showing a moisture characteristic similar to a normal cumulative distribution function, the derived pore size distribution is log normal. In this case, a direct identification technique is developed, yielding the parameters of the density function from the experimentalpF‐θrelationship. Practical applications demonstrate the validity of this probabilistic model, which gives good agreement with morphometric pore size data, available in the literature. The model also gives rise to an analytical expression for thepFcurve in terms of two structural parameters of the porous system, the mean and the standard deviation of the effective pore radi

ISSN:0043-1397    

DOI:10.1029/WR015i001p00107

年代:1979

数据来源: WILEY

摘要:

The vertical one‐dimensional assumption is examined with respect to its validity for mathematical ecological models of lakes or reservoirs. Analysis of the time and length scales characterizing the hydrodynamics, chemistry, and biology shows that the two scales are inexorably coupled and their interaction dictates both upper and lower bounds for the lake size that can be characterized by a one‐dimensional model. For an update frequency or forcing time scale of 1 day the one‐dimensional model is restricted to lakes characterized by length scales of 0.5–10 km. This range is preliminary and dependent on model formulation and update frequency. Inconsistencies between the model formulation scales for the hydrodynamics, chemistry, and biology may result in erroneous model pred

ISSN:0043-1397    

DOI:10.1029/WR015i001p00113

年代:1979

数据来源: WILEY

摘要:

The answer to the question posed in the title of this paper is yes, provided that some restrictions are imposed on the rainfall excess which is the input to the surface runoff system. Obviously, impulsive inputs are not admissible when the instantaneous unit hydrograph (IUH) has negative ordinates, since the IUH is the direct surface runoff response (known as the ‘Output’) to an instantaneous rainfall burst of unit volume and such runoff, by definition, cannot be negative. Is an instantaneous unit hydrograph with negative ordinates (IUHWNO) desirable? Now the answer is no, because of the restrictions that have to be imposed on the input. The purpose of this paper is not to justify the assumption of linearity, an assumption which is open to serious doubts, but rather to point out that IUHWNO can be of value if and when linearity of surface runoff systems is assumed. Two problems are considered: (1) The first is the ability of an IUHWNO to represent a real‐world surface runoff system. A ‘degenerate IUH’ does not have this ability, and hence the term ‘nondegenerate IUH’ is carefully defined in the paper. Several conditions are derived in the paper which enable decision as to the degeneracy of a given IUHWNO. (2) The second problem is the determination of the class of admissible inputs in a surface runoff system which is represented by a given nondegenerate IUHWNO. These two problems are relevant to whether or not one should explicitly introduce nonnegativity sign constraints into the IUH ordinates in the identification of a surface runoff system from input‐output records. Possible extensions to nonlinear and time‐varying systems are considered in the paper for continuous or disc

ISSN:0043-1397    

DOI:10.1029/WR015i001p00121

年代:1979

数据来源: WILEY

摘要:

Evaporation from a large hardwood forest is estimated from measurements of the required meteorological variables and from measured stomatal resistances. A correction factor is derived to overcome the incorrect assumption that evaporative demand remains the same during wet and dry periods. The factor is based on the ratio of the isothermal resistances during the wet and subsequent dry periods. The stomatal measurements were converted to canopy resistances by dividing by the leaf area index and were used to obtain the water balance for the entire season. The results are analyzed to show that evaporation from a wet canopy is often 2–3 times greater than transpiration from the same surface. Rates of interceptional loss, calculated from the wet and dry evaporation rates, were verified by direct measurements of throughfall and stemflow. Net interceptional loss, equal to the excess evaporation from a wet canopy over a dry one, depended on rainfall duration and character and was on the average about 60–80% of total interception, In the overall summer water balance of 442 mm of precipitation and 52‐mm depletion of soil storage, transpiration via the trees accounted for 261 mm; evaporation from the wetted leaves and branches for 111 mm, and runoff for 131 mm, giving an error of closure in the water balance of only 9 mm. If transpiration only had been used instead of interception when the canopy was wet, the error in the water balance would have been 1

ISSN:0043-1397    

DOI:10.1029/WR015i001p00131

年代:1979

数据来源: WILEY

摘要:

The theoretical absence of the in situ formation of most common mineral phases and the high vertical permeability of the relatively inert soils and unsaturated layer permit detection of man‐induced environmental changes in the dilute groundwater of Holt County. Correlation coefficients show many significant associations for the major ions in groundwater affected by point and nonpoint‐source contamination. Large areas of nonpoint contamination are attributed to fertilization and irrigation of the sandy soils. In these areas increases in the average annual groundwater concentrations of Cl−, SO42−, and NO3−average 0.44, 0.57, and 4.9 mg/l/yr, respectively. A proposed model suggests that 50% of the applied nitrogen fertilizer infiltrates to the groundwater

ISSN:0043-1397    

DOI:10.1029/WR015i001p00139

年代:1979

数据来源: WILEY

摘要:

The existence of a hydrologically uniform area is questionable. Therefore it is unlikely that a drainage basin can truly represent the diverse environmental and terrain conditions in any given area. The widely documented strong association between basin morphometry and hydrological responses indicates the possibility of identifying hydrologically similar basins on the basis of similarity of their gross morphology. By using a multidimensional morphological classification of drainage basins, a rational basis for the selection of representative basins is developed. The procedures for this classification and selection are outlined and illustrated with an example from southeastern Nigeria.

ISSN:0043-1397    

DOI:10.1029/WR015i001p00148

年代:1979

数据来源: WILEY

摘要:

By using the Bowen ratio method, hourly and daily evapotranspiration totals were determined during a drying period for a 9‐year‐old pine forest (Pinus sylvestris) situated in the upper Rhine area of Germany. A relationship between the soil water suction, expressed bypF, and the ratioQof the latent heat of evapotranspiration to the available energy was obtained. For 2

ISSN:0043-1397    

DOI:10.1029/WR015i001p00159

年代:1979

数据来源: WILEY