Catchment Topography Research Articles

Towards a catchment‐scale model of subsurface runoff generation based on synthesis of small‐scale process‐based modelling and field studies

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 small‐scale flow processes.

Study on Extracting Drainage Networks from Square-grid DEMs

Recently, Digital Elevation Models (DEMs) can be often used in the analysis of catchment topography and hydrological process. Some methods that extract drainage networks from square-grid DEMs are proposed. They make use of the flow-accumulation-value threshold for extracting drainage networks from delineated overland flow paths, but the relationship between chanel length, L, and catchment area, A, of the external link in the drainage network from DEMs is different from that of actual drainage networks. This paper proposes a new threshold, which is defined by the ratio of the width, w, to the penetrated length, l, in a contour line.As a result, it shows that this relation is improved. Furthermore, we examine the hydrologic response of both drainage networks, and represent effects of the threshold for this response.

Modelling hydrology of agricultural catchments using parameters derived from rainfall simulator data

The ANSWERS model was modified to include a multi-layer, transient conductivity infiltration equation, based on the Green and Ampt equation, capable of simulating infiltration into soils which develop a surface seal under rain. Prediction of runoff hydrographs with the modified model was tested for 88-m 2 rainulator plots and cultivated catchments of 0.07 and 3.2 ha, using infiltration parameter values derived from data from 1-m 2 rainfall simulator plots. All other parameters were either measured (e.g. catchment topography, cover) or estimated from published values (e.g. Manning's n) based on conditions observed in the field. No calibration or fitting of the model to runoff data were used. Preliminary results of the study are presented. Prediction of the runoff hydrograph for rainulator plots was excellent. Good prediction of hydrographs was obtained for the catchments. Infiltration parameters from 1-m 2 rainfall simulator plots appear to be appropriate for modelling runoff for these “simple” catchments when the infiltration method used in the model is physically realistic, and the model takes into account the spatial and temporal nature of the ensuing overland and channel flow. The results are sufficiently encouraging that validation for further events and more complex catchments will be undertaken.

Digital terrain modelling: A review of hydrological, geomorphological, and biological applications

AbstractThe topography of a catchment has a major impact on the hydrological, geomorphological, and biological processes active in the landscape. The spatial distribution of topographic attributes can often be used as an indirect measure of the spatial variability of these processes and allows them to be mapped using relatively simple techniques. Many geographic information systems are being developed that store topographic information as the primary data for analysing water resource and biological problems. Furthermore, topography can be used to develop more physically realistic structures for hydrologic and water quality models that directly account for the impact of topography on the hydrology. Digital elevation models are the primary data used in the analysis of catchment topography. We describe elevation data sources, digital elevation model structures, and the analysis of digital elevation data for hydrological, geomorphological, and biological applications. Some hydrologic models that make use of digital representations of topography are also considered.

Baptiste Lake, Alberta ? A late Holocene history of changes in a lake and its catchment in the southern Boreal forest

Palaeoenvioonmental investigations based upon sediment cores retrieved from Baptiste Lake, Alberta (longitude 114° 34′ W; latitude 54° 45′ N) show that the sedimentary record spans approximately 4600 years. The pollen record reflects the dynamic nature of the southern boreal forest. These dynamic changes are reflected in the lake record itself. Climate and vegetation do not appear to have changed significantly; however, the lake does appear to have responded to climate change, particularly during the last 1000 to 700 years when temperatures decreased to modern values. It is at this time that there is a marked change from laminated to unlaminated sediments suggesting a change from meromixis to one where complete circulation takes place. As a result monolimnetic nutrients are released into the epilimnion. Catchment perturbations have occurred with fire appearing most important. Sedimentation rates are high on average and irregular, due in part to the many inflowing streams, catchment topography and fire. Lake production has always been high. Carbonate bands occur in the core at irregular intervals and appear to originate biogenically. Peaks in the number of pyrite spherules suggest that deoxygenation of the water column occurs irregularly, and the intensity of anaerobic conditions again varies. The diatom record indicates a eutrophic lake with Stephanodiscus hantzschii the dominant species. The lake appears to have steadily become more eutrophic with time and a succession of species has occurred with Asterionella formosa being succeeded in turn by Stephanodiscus niagare, Cyclotella comta and finally, Melosira granulata. The appearance of Melosira granulata corresponds to the change from laminated to unlaminated sediments, and to then both autochthonous and allochthonous nutrient input.

The relationship of catchment topography and soil hydraulic characteristics to lake alkalinity in the northeastern United States

We undertook the task of determining whether base flow alkalinity of surface waters in the northeastern United States is related to indices of soil contact time and flow path partitioning that are derived from topographic and soils information. The influence of topography and soils on catchment hydrology has been incorporated previously in the variable source area model TOPMODEL as the relative frequency distribution of ln (a/Kb tan B), where ln is the Naperian logarithm, “a” is the area drained per unit contour, K is the saturated hydraulic conductivity, b is the soil depth, and tan B is the slope. Using digital elevation and soil survey data, we calculated the ln (a/Kb tan B) distribution for 145 catchments. Indices of flow path partitioning and soil contact time were derived from the ln (a/Kb tan B) distributions and compared to measurements of alkalinity in lakes to which the catchments drain. We found that alkalinity was, in general, positively correlated with the index of soil contact time, whereas the correlation between alkalinity and the flow path partitioning index was weak at best. A portion of the correlation between the soil contact time index and alkalinity was attributable to covariation with soil base saturation and cation exchange capacity, while another portion was found to be independent of these factors. Although our results indicate that catchments with long soil contact time indices are most likely to produce high alkalinity base flow, a sensitivity analysis of TOPMODEL suggests that surface waters of these same watersheds may be susceptible to alkalinity depressions during storm events, due to the role of flow paths.

Effects of spatial variability and scale with implications to hydrologic modeling

This paper reports the results of a preliminary investigation into the existence of a Representative Elementary Area (REA) in the context of hydrologic modeling at the catchment scale. The investigation was carried out for an actual catchment topography as represented by Coweeta River experimental basin with synthetic realizations for rainfall and soils. The hydrologic response of this catchment was modeled by a modified version of topmodel ★ ★ Beven and Kirkby (1979) which is capable of modeling both infiltration excess and saturation excess runoff and incorporating the spatial variability of soils, topography, and rainfall. The effect of scale was analyzed by first dividing the catchment into smaller subcatchments and determining the average water fluxes for each subcatchment. The preliminary results lead to the following conclusions: (1) a Representative Elementary Area (REA) exists in the context of catchment hydrologic responses; (2) the REA is strongly influenced by the topography; and (3) based on our initial results, the length scale of rainfall seems to have only a secondary role in determining the size of the REA; however, increases in the variability of rainfall and soils between subcatchments increase the variability of runoff generation between subcatchments.

On hydrologic similarity: 2. A scaled model of storm runoff production

The paper describes a simple physically based conceptual model of runoff production based on catchment topography and the spatial variablity of rainfall and soil properties. Both infiltration excess (Horton type) and saturation excess (Dunne type) runoff production mechanisms are considered. The effect of topography is modeled using the In (α/tan β)‐topographic index method of Beven and Kirkby (1979). The effects of the spatial variability of soil properties and rainfall on areal average infiltration rates are handled using a quasi‐analytical approach. The interaction between the two mechanisms of runoff production and the effect of a finite water table on the infiltration excess mechanism are explicitly considered. The model equations are cast in a dimensionless form to clarify the interrelationships involved in hydrological responses and to identify measures of similarity between different heterogeneous catchments. The dimensionless formulation has led to the identification of five similarity parameters and three dimensionless variables representing initial conditions and storm characteristics. Finally, a number of experiments were performed to study the sensitivity of the runoff production response to some of these similarity parameters.

Impact of the 1983 wildfires on river water quality in East Gippsland, Victoria

Eleven stream stations within the basins of the Bemm, Cann, Thurra, Wingan and Genoa Rivers were sampled during a 3-month interval following a prolonged drought and intense and extensive forest fires. Emphasis was placed on flows resulting from three major storms that occurred during this period. Water-quality impacts of the fires were intermingled with those of the preceding drought, and flow- related comparisons with pre-drought data showed appreciable increases in colour, turbidity, suspended solids, potassium and nitrogen levels in the Bemm River, which was only marginally affected by the fires. In the Cann and Genoa Rivers, with much larger proportions of catchment burnt, electrical conductivity and phosphorus concentrations also rose substantially. Marked depletion of dissolved oxygen (to <6 mg I-1) was unique to streams with burnt catchments, but resulted from stagnant conditions at the end of the drought as well as from changes occurring at the time of the first post-fire storm. The fires had little obvious effect on temperature and pH regimes. Peak turbidities and concentrations of suspended solids and phosphorus were much greater in the Cann and Genoa river systems than elsewhere. Maximum values for these indicators were 130 NTU, 2300 mg I-1 and over 0.8 mg I-1, respectively. In the Thurra and Wingan basins, which were also burnt, stream suspended-solids levels were lower (<200 mg I-1), but solutes sometimes reached very high maxima (indicated by peak electrical conductivities of up to 110 mS m-1). Variations in catchment topography and soils and the relative importance of surface and subsurface flow probably account for these differences. The first post-fire storm produced the highest measured levels of many indicators in most streams, although the greatest flows were associated with the third storm. Nitrite and ammonia were notable exceptions to this generalization. Estimates of catchment exports indicated high sediment yields and moderate to high phosphorus yields from the Cann and Genoa catchments, by comparison with other Australian data.

Determination of design hydrographs on small catchments by the state variable model

Derivation of a design hydrograph from rainfall data is a typical problem when dealing with small catchments; in most cases there are no streamflow data available. Numerical solutions of unsteady flow equations are difficult to adopt for flow on natural catchments because of the uncertainity about the initial and boundary conditions. A simplified approach is suggested in which a catchment topography is characterized by a number of planes and channels. Flow over the planes and the channel flow are computed by a numerical solution of the state variable equations of unsteady gradually varied flow. The state variable model of surface flow offers simplicity and calculating speed compared with the numerical solutions of the complete unsteady flow equations, yet it maintains a reasonable approximation of the physical reality. Example problems of the use of the model in derivation of a design hydrograph for a small catchment, using rainfall intensities and durations as inputs, are presented. The computer program is provided at a nominal charge from the Depository of Unpublished Data, CISTI, National Research Council of Canada, Ottawa, Canada K1A 0S2.