ISSN:0885-6087    

DOI:10.1002/hyp.3360090502

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThis is the second in a series of three papers about the meta‐channel concept which illustrates the derivation of the principles behind the concept, the construction of the hydraulic geometry and the application of the concept to flood routing, respectively. It was shown in the first of these that a channel network in a catchment can be conceptualized into a single ‘effective channel’ representation: a meta‐channel. This study uses this conceptualization to show how such a meta‐channel can be constructed. The techniques derived are applied to one catchment in New Zealand. We derive hydraulic geometries expressed as functions of flow distance throughout this catchment based on the Leopold and Maddock power laws. This derivation uses classical published values for hydraulic geometry coefficients and exponents, regional parameterization of the index flood relationship for New Zealand as a whole, together with local knowledge regarding the order of magnitude of the channel roughness. Conservation principles derived from the continuity and mechanical energy balance equations are used to construct the hydraulic geometry of the meta‐channel of this catchment. A meta‐channel long profile is established and compared against the mainstream long profile. The effectiveness of the Leopold and Maddock power law assumptions is tested by comparing the derived hydraulic geometry against available field cross‐sectional data for the gauging site at the outlet o

ISSN:0885-6087    

DOI:10.1002/hyp.3360090503

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractIt is argued that the aggregation approach towards macroscale hydrological modelling, in which it is assumed that a model applicable at small scales can be applied at larger scales using ‘effective’ parameter values, is an inadequate approach to the scale problem. It is also unlikely that any general scaling theory can be developed due to the dependence of hydrological systems on historical and geological perturbations. Thus a disaggregation approach to developing scale‐dependent models is advocated in which a representation of the distribution of hydrological responses is used to reflect hydrological heterogeneity. An appropriate form of distribution may vary with both scale and environment. Such an approach is dependent on the data available to define and calibrate the chosen subgrid parameterization. A parameterization based on a minimum patch representation is suggested and the problems of identification at the larger scale disc

ISSN:0885-6087    

DOI:10.1002/hyp.3360090504

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractExtrapolation of measurements of water use by individual trees to that for a stand of trees is a critical step in linking plant physiology and hydrology. Limitations in sampling resources and variation in tree sizes within a stand necessitate the use of some scaling relationship. Further, to scale tree water use in space as well as time, the relationship must reflect the changing availabilities of energy and water supply. It is argued here that tree leaf area is the most appropriate covariate of water use to achieve this aim. However, empirical results show that the relationship is not always linear. A theory is developed, based on the concepts of hydrological equilibrium (sensuNemani and Running, 1989) and ecological field theory (Walkeret al., 1989) which accounts for (occasional) non‐linear behaviour of the flux/ leaf area relationship in evergreen trees. A key feature of this theory is the notion of a non‐linear, quasi‐equilibrium reflecting plant water stress. An equation is derived from these concepts and a standard, explicit treatment of tree water use (Landsberg and McMurtrie, 1984), which is used to characterise this relationship. This equation has the formQ=aIA+bΨsAf.The theory is tested against field data and published reports onEucalyptustree wat

ISSN:0885-6087    

DOI:10.1002/hyp.3360090505

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractMethodologies for developing a macro‐scale model of subsurface stormflow generation on a steep forested catchment in Japan are addressed. Field studies on this catchment have indicated that subsurface flow, consisting mainly of ‘old’ water displaced by ‘new’ rain water, dominates the storm response. Detailed field measurements on the catchment allowed simple, catchment‐scale relationships to be developed between the volume of saturated groundwater, on the one hand, and discharge, and surface and subsurface saturated areas, on the other. Attempts are made to find linkages between these empirical relationships and physically‐based descriptions of hydrological processes operating at smaller scales. A distributed model based on the saturated‐unsaturated groundwater flow on steep catchments was developed and tested with field data collected on this catchment. Derivation of catchment‐scale relationships can be carried out by a straightforward integration of the distributed model output. An alternative disaggregation‐aggregation approach is presented, whereby the catchment is divided into a number of hillslope flow strips. By applying the distributed model on each flow strip, under steady‐state conditions, it is possible to infer the spatial variability of groundwater volume in the various flow strips. This variability is related to a measure of hillslope topography and geometry. Knowing the catchment topography and geometry for any catchment, it is then possible to derive useful catchment‐scale relationships which are applicable under quasi‐steady‐state conditions. Hydrological relationships derived in this manner are compared with corresponding empirical relationships. The methodologies presented are effective for understanding the linkages between catchment scale response and

ISSN:0885-6087    

DOI:10.1002/hyp.3360090506

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractRunoff generation in natural catchments due to storm rainfall is highly complex and spatially and temporally heterogeneous. In recent work on seven small experimental catchments Larsenet al.(1994) showed that underlying the heterogeneity of runoff generationwithinthe catchments, there is a degree of regularitybetweenthe catchments that could be quantified in terms of two dimensionless similarity parametersK0* andf*. These two parameters, constants for a catchment, were able to characterize the relative dominance of the saturation excess (Dunne‐type) and infiltration excess (Horton‐type) mechanisms of runoff generation. Given thatK*0andf* can characterize the type of runoff generation on any catchment, it may follow that they can be used to define a catchment‐scale runoff generation model. This idea is pursued in this paper. For the same catchments as studied by Larsenet al.(1994), a lumped, physically based model is developed that describes both the extent of saturated areas and the average infiltration capacity of the unsaturated areas during a storm. This is achieved by utilizing the distributed model used by Larsenet al.(1994) to aggregate the point‐scale runoff generation responses, up to the catchment scale, from which the functional form and the parameters of the catchment‐scale runoff generation model are inferred. The parameters of this lumped model are defined entirely in terms of the underlying distribution of topography, three similarity parametersK*0,f* andB*, the normalized average water‐table depth,z*, and the normalized cumulative volume of infi

ISSN:0885-6087    

DOI:10.1002/hyp.3360090507

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractAddressing scaling issues in hydrological modelling involves, among other things, the study of problems related to hydrological similarity between catchments of different scales. Recent research about catchment similarity relationships is based on distributed conceptual models of surface runoff production. In this type of hydrological modelling both infiltration excess and saturation excess runoff production mechanisms are considered. In many humid lowland areas overland flow is a rare phenomenon because of the specific conditions that prevail: moderate rainfall, high infiltration capacity and low relief. The complete drainage system in these regions consists of surface and subsurface components which have organized themselves in a given geological, geomorphological and climatic situation. A surface drainage network has developed through sapping erosion at the zone of groundwater exfiltration. The resulting hierarchical stream network is in equilibrium with large time‐scale conditions and adjusts itself dynamically to the inter‐year and seasonal meteorological fluctuations. Greater understanding of the interrelationships that underlie the storm response of catchments in humid lowland regions can be expected by focusing on stream network morphology as a function of topography, geology and climate. This paper applies the physically based mathematical model of stream network morphology, developed by De Vries (1977), to the Zwalmbeek catchment, Belgium. Based on this model and for different climatic conditions (expressed in terms of rainfall characteristics) the first‐order stream spacing versus average water‐table depth relationship is calculated. From field observations, digital elevation model derived channel network drainage densities and flood event analysis it is concluded that the 1% exceedance probability rainfall can be suggested as representative for the shaping climatic conditions in the catchment under study. The corresponding curves relating channel network characteristics, such as stream spacing, drainage density and channel geometry, to average water‐table depth are basin descriptors and could be used for comparative studies (e.g. regional flood frequency analysis). The model further allows for the prediction of the expansion and shrinkage of the first‐order channel network as a function of catchment wetness expressed in terms of the effective water

ISSN:0885-6087    

DOI:10.1002/hyp.3360090508

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThis paper, part review and part new work, falls into three main sections. The first is a review of scale issues in both hydrology and meteorology, focusing on their origins in the water and energy conservation equations, integrated over control volumes of different scales. Several guidelines for scale translations are identified.The second section reviews the upscaling problem in boundary‐layer meteorology, setting out two ‘flux‐matching’ criteria for upscaling models of land‐air fluxes: the conservation requirement that surface fluxes average linearly and the practical requirement that model form be preserved between scales. By considering the effects of boundary conditions, it is shown that the combination or Penman‐Monteith equation is a model for elemental energy fluxes which leads to physically consistent flux‐matching rules for upscaling surface descriptors (resistances). These rules are tested, along with some other possibilities, and found to perform well.The third section tests the hypothesis that regionally averaged energy balances over land surfaces are insensitive to the scale of heterogeneity,X. Heterogeneity is classified as microscale whenX⩽UmT*, mesoscale whenUmT* ⩽X⩽UmTe, and macroscale whenUmTe⩽X[whereUmis the mean wind speed in the convective boundary layer (CBL) andT* andTethe convective and entrainment time scales, respectively]. A CBL slab model is used to show that regionally averaged energy fluxes are remarkably insensitive toXin both the microscale and macroscale ranges. Other reviewed evidence suggests that the mesoscale range behaves similarly in dry conditions. Questions remain about the consequences of clouds and precipitation for regionally averaged

ISSN:0885-6087    

DOI:10.1002/hyp.3360090509

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractModelling experiments have been undertaken to address the effects of land surface heterogeneity on the energy and water fluxes at catchment scales. The simulation results indicate that in the presence of strong contrasts (i.e. patchiness) in the land surface characteristics (for example, soil moisture, leaf area index or vegetation type) significant inter‐patch advection can result. For example, small areas with high levels of soil moisture surrounded by drier areas have a disproportionately high latent heat flux. The sensible heat flux showed a complementary suppression. The response to changes in leaf area index, however, was found to be much more complex. At constant soil moisture levels, it was found that under some conditions the latent heat flux of patches of high leaf area index increased as its proportion of the surface increased as a result of the increase in net radiation and roughness. There was also an increase in sensible heat flux. This effect was also found on surfaces with low moisture levels and strong contrasts in surface vegetation. Although these results do depend on the initial boundary layer and terrestrial conditions, a consequence of this is that significant biases can be generated in modelling catchment output if the heterogeneity effects are not fully accounted for. The model simulations demonstrate that the fluxes from a ‘homogenized’ surface with catchment‐average land surface properties (e.g. soil moisture) can be significantly higher than that for a heterogeneous surface with explicitly modelled inter‐patch interactions. These results have particular implications for nested catchment models where the responses of individual subcatchments are as important as that of the total catchment. They are also significant in efforts towards developing lumped land surface parameterizations for use in atmospheric models such as general circulati

ISSN:0885-6087    

DOI:10.1002/hyp.3360090510

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractSurface observations and NOAA advanced very high resolution radiometer (AVHRR) satellite data are combined to provide area‐averaged values of albedo, canopy resistance, leaf area index and fractional vegetation cover. Albedo, fractional vegetation cover and leaf area index are derived from the reflectance of the visible and infra‐red NOAA AVHRR channels. Canopy resistance is estimated by closing the surface energy balance equation using the surface infra‐red temperature and the normalized difference vegetation index. These land surface parameters are evaluated against independent measurements and used as input into a numerical model to simulate the energy exchange between the surface and the overlying atmosphere. Simulation results are validated against detailed aircraft observations undertaken in south‐western Australia over both natural and agricultural veg

ISSN:0885-6087    

DOI:10.1002/hyp.3360090511

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY