Catchment Shape Research Articles

Adjustment of Peak Streamflows of a Tropical River for Urbanization

Peak runoff from a catchment is influenced by many factors such as intensity and duration of rainfall, catchment topography, catchment shape, land use and other variables. For a particular catchment, landuse change and other human activities will alter the characteristic of catchment hydrograph. Problem statement: As a result of urbanization, the magnitude of floods occurring in a catchment increased. It was found that the land use change in the Langat River catchment has clear impact on annual peak streamflow record, particularly from 1983-2003 while, the change has no significant impact on streamflow record from 1960-1982. Spatial data confirms the heavy development occurred in river basin from 1983-2003. Thus, urbanization makes the historical record of Langat River non-homogenous and this makes the mathematical simulation for the record inappropriate due to poor expected output. Approach: In this study, historical record of Langat River, Selangor, Malaysia from 1960-2003 was used to study the impact of urbanization on the streamflow. The annual peak streamflow was selected for this purpose. The peak streamflow record was divided into two sets. Set one from 1960-1982 and set two from 1983-2003, which represent periods before and after urbanization, respectively. To adjust the set one data for urbanization, different adjustment factors were used to make the data homogeneous. Normal model was applied to find the best factor for model fitness. Results: The best adjustment factors were selected by trial and error technique based on 95% confidence level. To determine the optimum adjustment factors from the best ones, the point of intersection between the homogeneity and Normal model evaluation curves was located. This point represented the optimum adjustment factor and its value was found to be 1.9. Autorun model was used to validate the above finding and it was found that the model prediction is acceptable with reasonable accuracy. Conclusion/Recommendations: The proposed method can be recommended to be used for predicting the streamflow of Langat River considering the impact of urbanization on the streamflow. The method also, is applicable to adjust a flood record for which flood events had occurred on a watershed undergoing continuous changes in levels of urbanization to meet both homogeneity and best model fitness.

Predicting catchment sediment yield in Mediterranean environments: the importance of sediment sources and connectivity in Italian drainage basins

AbstractPredicting sediment yield at the catchment scale is one of the main challenges in geomorphologic research. The application of both physics‐based models and regression models has until now not provided very satisfying results for prediction of sediment yield for medium to large sized catchments (c. >50 km2). The explanation for this lies in a combination of the large data requirements of most models and a lack of knowledge to describe all processes and process interactions at the catchment scale. In particular, point sources of sediment (e.g. gullies, mass movements), connectivity and sediment transport remain difficult to describe in most models. From reservoir sedimentation data of 44 Italian catchments, it appeared that there was a (non‐significant) positive relation between catchment area and sediment yield. This is in contrast to what is generally expected from the theory of decreasing sediment delivery rates with increasing catchment area. Furthermore, this positive relation suggests that processes other than upland erosion are responsible for catchment sediment yield. Here we explore the potential of the Factorial Scoring Model (FSM) and the Pacific Southwest Interagency Committee (PSIAC) model to predict sediment yield, and indicate the most important sediment sources. In these models different factors are used to characterize a drainage basin in terms of sensitivity to erosion and connectivity. In both models an index is calculated that is related to sediment yield. The FSM explained between 36 and 61 per cent of the variation in sediment yield, and the PSIAC model between 57 and 62 per cent, depending on the factors used to characterize the catchments. The FSM model performed best based on a factor to describe gullies, lithology, landslides, catchment shape and vegetation. Topography and catchment area did not explain additional variance. In particular, the addition of the landslide factor resulted in a significantly increased model performance. The FSM and PSIAC model both performed better than a spatially distributed model describing water erosion and sediment transport, which was applied to the same catchments but explained only between 20 and 51 per cent of the variation in sediment yield. Model results confirmed the hypothesis that processes other than upland erosion are probably responsible for sediment yield in the Italian catchments. A promising future development of the models is by the use of detailed spatially distributed data to determine the scores, decrease model subjectivity and provide spatially distributed output. Copyright © 2006 John Wiley & Sons, Ltd.

Nash 모형의 지체시간을 이용한 GIUH 유도

The lag time is one of the most important factors for estimating a flood runoff from streams. It is well known to be under the influence of the morphometric properties of basins which could be expressed by catchment shape descriptors. In this paper, the notion of the geometric characteristics of an equivalent ellipse proposed by Moussa(2003) is applied for calculating the lag time of geomorphological instantaneous unit hydrograph(GIUH) at the basin outlet. The lag time is obtained from the observed data of rainfall and runoff by using the method of moments suggested by Nash(1957), and the procedure based on geomorphology is used for GIUH. The relationships between the basin morphometric properties and the hydrological response are discussed as applied to 3 catchments In Korea. Additionally, the shapes of equivalent ellipse are examined how then are transformed from upstream area to downstream one. As a result, the relationship between the hydrological response and descriptors is shown to be comparatively good, and the shape of ellipse is presented to approach a circle along the river downwards. These results may be expanded to the estimation of hydrological response of ungauged catchment.

Hydrological and watershed characteristics of the El‐Kabir River, North Lebanon

AbstractThe El‐Kabir River watershed is the largest in western Lebanon and is shared between Lebanon and Syria. The river forms most of the northern boundary of Lebanon with Syria, being characterized by water flow throughout the year. The characteristics of the river and its variable hydrologic properties are the result of abrupt changes in land physiography. Until recently, data on Lebanese rivers was inadequate, especially for rivers shared with other countries. The El‐Kabir River watershed typifies this situation, particularly when the river has undergone many changes, including water pollution and declining discharge because of changing climate and increased pollution. This study was implemented in the context of a large investigation of the watershed which was funded by the International Development Research Council, Canada, for the purpose of improving the baseline data and knowledge required to effectively manage this important resource. Within the water cycle, ≈ 250 × 106 m3 of precipitation falls on the Lebanese side. Of this volume, ≈ 50% is lost as evaporation and transpiration, while 5–50% of the remainder infiltrates to ground water, with the residual becoming land run‐off. An obvious decline of ≈ 40% of the total river discharge of the river has occurred over the last 50 years. It can be explained by climate change and by water extraction associated with dramatic increases in population and associated land uses. The hydraulic configuration and characteristics of the river have two major orientations; namely, NE–SW and E–W. These orientations are the product of geological structure and lithologies. Furthermore, each has different hydrologic properties related to watershed size, elevation, slope, catchment shape and orientation, although both orientations are directly inter‐related.

신집수형상디스크립터와 Nash 모형의 지체시간 사이의 상관성 분석

본 연구는 Moussa(2003)에 의하여 개발된 등가타원을 기반으로 한 신집수형상디스크립터에 대한 소개 및 수문학적 적용성 평가를 목적으로 한다. 두 디스크립터 a+b, a+b+<TEX>${\varepsilon}OM$</TEX>과 지체시간 사이의 상관성 분석이 수행되었고 이를 Nash 모형 매개변수들의 대표치 산정에 적용하였다. 본 연구의 실용성을 조사하기 위하여 한강 수계의 평창강 유역, 금강 수계의 보청천 유역 그리고 낙동강 수계의 위천 유역들에 각각 이 디스크립터특이 적용되었다. 그 결과, 두 디스크립터는 양자 모두 고전적 지형인자들에 비하여 지체시간과 높은 상관성을 보여 Moussa(2003)가 제시한 연구 결과를 국내 유역으로부터 확인할 수 있었고 실제 적용강의 간편성을 위하여 전자가 추천된다. 또한 본 연구로부터 유도된 대표순간단위도들은 일관성 있는 유역응답특성을 보여 신집수형상디스크립터의 수문학적 적용성을 확인 할 수 있었다. 앞으로 보다 많은 유역들에 대한 사례분석이 필요한 것으로 판단된다. This study aims at the introduction of new catchment shape descriptor, developed by Moussa(2003), based on equivalent ellipse and the assessment of its hydrologic applicability. Two descriptors a+b and a+b+<TEX>${\varepsilon}OM$</TEX>were correlated to the lag time and those were applied to the estimation of representative values of Nash model parameters. They are applied in order to examine the practicality to 3 catchments in Korea, catchments in Korea, respectively, i.e. Pyeongchanggang catchment in Han river, Bocheongcheon catchment in Geum river and Wicheon catchment in Nakdong river. As a result both of two descriptors show higher correlations to the lag lime than classical geomorphologic factors and hereby Moussa's suggestion(2003) is confirmed. For the sake of simplicity the former is recommended. Also representative IUHs derived from this study show consistent basin response characteristics. It is desirable to conduct further more case studies on many other basins.

A qualitative and quantitative evaluation of experimental model catchment evolution

AbstractDue to the geological time scales required for observation of catchment evolution, surrogates or analogues of field data are necessary to understand long‐term processes. To investigate long‐term catchment behaviour, two experimental model catchments that developed without rigid boundaries under controlled conditions are examined and a qualitative and quantitative analysis of their evolution is presented. Qualitatively, the experimental catchments have the visual appearance of field scale data. Observation demonstrates that changes in catchment shape and network form are conservative. Quantitative analysis suggests that the catchments reach an equilibrium form while a reduction in the channel network occurs. While the catchments are laboratory scale models, the results provide insights into field scale behaviour. Copyright © 2003 John Wiley &amp; Sons, Ltd.

On morphometric properties of basins, scale effects and hydrological response

AbstractOne of the important problems in hydrology is the quantitative description of river system structure and the identification of relationships between geomorphological properties and hydrological response. Digital elevation models (DEMs) generally are used to delineate the basin's limits and to extract the channel network considering pixels draining an area greater than a threshold area S. In this paper, new catchment shape descriptors, the geometric characteristics of an equivalent ellipse that has the same centre of gravity, the same principal inertia axes, the same area and the same ratio of minimal inertia moment to maximal inertia moment as the basin, are proposed. They are applied in order to compare and classify the structure of seven basins located in southern France. These descriptors were correlated to hydrological properties of the basins' responses such as the lag time and the maximum amplitude of a geomorphological unit hydrograph calculated at the basin outlet by routing an impulse function through the channel network using the diffusive wave model. Then, we analysed the effects of the threshold area S on the topological structure of the channel network and on the evolution of the source catchment's shape. Simple models based on empirical relationships between the threshold S and the morphometric properties were established and new catchment shape indexes, independent of the observation scale S, were defined. This methodology is useful for geomorphologists dealing with the shape of source basins and for hydrologists dealing with the problem of scale effects on basin topology and on relationships between the basin morphometric properties and the hydrological response. Copyright © 2002 John Wiley &amp; Sons, Ltd.

Heterogeneity in catchment properties: a case study of Grey and Buller catchments, New Zealand

Abstract. The scaling behaviour of landscape properties, including both morphological and landscape patchiness, is examined using monofractal and multifractal analysis. The study is confined to two neighbouring meso-scale catchments on the west coast of the South Island of New Zealand. The catchments offer a diverse but largely undisturbed landscape with population and development impacts being extremely low. Bulk landscape properties of the catchments (and their sub-basins) are examined and show that scaling of stream networks follow Hack’s empirical rule, with exponents ∼0.6. It is also found that the longitudinal and transverse scaling exponents of stream networks equate to νl ≈0.6 and νw≈ 0.4, indicative of self-affine scaling. Catchment shapes also show self-affine behaviour. Further, scaling of landscape patches show multifractal behaviour and the analysis of these variables yields the characteristic parabolic curves known as multifractal spectra. A novel analytical approach is adopted by using catchments as hydrological cells at various sizes, ranging from first to sixth order, as the unit of measure. This approach is presented as an alternative to the box-counting method as it may be much more representative of hydro-ecological processes at catchment scales. Multifractal spectra are generated for each landscape property and spectral parameters such as the range in α (Holder exponent) values and maximum dimension at α0, (also known as the capacity dimension Dcap), are obtained. Other fractal dimensions (information Dinf and correlation Dcor) are also calculated and compared. The dimensions are connected by the inequality Dcap≥Dinf≥Dcor. Such a relationship strongly suggests that the landscape patches are heterogeneous in nature and that their scaling behaviour can be described as multifractal. The quantitative parameters obtained from the spectra may provide the basis for improved parameterisation of ecological and hydrological models. Keywords: fractal, multifractal, scaling, landscape, patchiness

On the effect of digital elevation model accuracy on hydrology and geomorphology

This study compares published cartometric and photogrammetric digital elevation models (DEMs) of various grid spacings with a ground truth data set, obtained by ground survey, and studies the implications of these differences on key hydrologic statistics. Inferred catchment sizes and stream networks from published DEMs were found to be significantly different than those from the ground truth in most instances. Furthermore, the width functions and cumulative area relationships determined from the published DEMs were found to fall consistently outside the 90% confidence limits determined from the ground truth for more than 60% of the relationship, suggesting that these hydrologic properties are poorly estimated from published DEMs. However, the slope‐area relationships determined from published DEMs were found to be less sensitive to catchment shape, size, and stream network, with the relationship falling outside the 90% confidence limits for less than 40% of the relationship for all catchments identified from the published DEMs. A published relationship linking the horizontal resolution with the vertical accuracy of the DEM was tested, predicting a horizontal resolution of about 10 m for the published DEMs tested.

A strategy to build a macro hydrological model to be coupled to an atmospheric model

To successfully model global energy and water cycles, the linkage of the hydrologic model and atmospheric model is required. We present a strategy to build a macro hydrological model to be combined to an atmospheric model.First we present a way to combine the field models of the atmospheric and hydrologic systems, in which the natural catchment shapes can be used as macro hydrological grids. This makes us to utilize the experience in hydrological modeling of watersheds.Second we present a strategy to build simplifieddistributed hydrological models of the processes within each macro hydrological grid. We take into account topography and stream network structure to derive simplified models, using the cluster analysis and stream order analysis. This type of simplification will be useful when considering the heterogeneity of hydrological state variables within a grid.

Fractal analyses of tree-like channel networks from digital elevation model data

Digital elevation models (DEMs) are generally used to automatically map the channel network and to delineate subbasins. The most common approach to extract a channel network from DEMs consists of specifying a threshold area S which is the minimum area required to drain to a point for a channel to form. This threshold area is usually specified arbitrarily, although it is recognized that different threshold areas will result in substantially different channel networks for the same basin. In this paper, we study the effect of S (that is also the scale of observation) on the morphometric properties (external and internal links, length of drainage paths, mainstream length) and scaling properties (such as Horton's and Strahler's laws, and fractal dimension). Three basins, located in southern France, were extensively studied. The results indicate that morphometric properties vary considerably with S, and thus values reported without their associated S should be used in hydrologic analysis with caution. Then, the fractal geometry is used to take into account the dependence of measured values on observation scales, which is not possible with classical hydrological indexes. The use of fractals allows, first, to point out self-similarity in the structure of channel networks and then to quantify the tree-like organization. New catchment shape indexes, independent of the observation scale S, are defined. These indexes are useful for comparing catchments and for measuring the irregularity level of the channel network.

Well catchments and time‐of‐travel zones in aquifers with recharge

The classical analytical method used to map catchments and time‐of‐travel zones of pumping wells was originally derived for another purpose and takes no account of recharge (Bear and Jacobs, 1965). Generalized catchment shapes are presented here for aquifers with recharge. They can be scaled to field situations through two or three nondimensional parameters. A semianalytical path line tracing model was used to generate the shapes. It contains new expressions for pore water velocities in two infinite strip, recharged aquifers, one with two fixed head boundaries, the other with one impermeable boundary. The resulting catchments differ significantly in both shape and size from catchments estimated by the no‐recharge method. Generalized results are also presented for time‐of‐travel zones which are noticeably smaller than those calculated by the no‐recharge method. Comparison with an equivalent recently released model from the U.S. Environmental Protection Agency shows the latter to give poor estimates of catchments and time‐of‐travel zones.

Comparison of Overland Flow Hydrograph Models

The diffusion equation is a simplification of the two‐dimensional continuity and momentum equations. This simpler dynamic model of two‐dimensional hydraulics affords the hydrologist a means to quickly estimate floodflow effects for overland flow. A numerical model using the diffusion approach (DHM) is applied to a set of idealized catchments in order to develop synthetic unit hydrograph S‐graph equivalents. The model is based on an explicit, integrated finite‐difference scheme, and the catchment is represented by topographic elevation and geometric data. Synthetic unit hydrographs (S‐graphs) developed from use of the DHM are used to advance interesting relationships between the unit hydrograph lag factor and the constant effective rainfall intensity used to generate the S‐graphs. Sensitivity of the synthetic S‐graphs to variations in idealized catchment size, slope, shape, friction parameters, and effective rainfall intensity are examined. Comparisons between linear and nonlinear unit hydrograph models, a...

Hydrologic behaviour of a small forested catchment

The variations in discharge along a reach of stream emanating from a spring at the head of a small steep forested catchment in southeastern Australia were measured over a 4-yr. period. The results showed that the outflow of the springhead catchment was considerably less variable than the outflow of the catchment flanks along the length of the stream. Following substantial periods of rainfall the peak discharges from the springhead were reached some days after the cessation of rain, while the peak discharges from the flank catchment were reached during or immediately after the period of rainfall. Diurnal variations in summer streamflows were not observed at the springhead, but were observed with an increasing amplitude as distance downstream from the springhead increased. Field studies and mathematical analysis indicated that neither overland flow nor channel interception of rainfall were important in generating the streamflow response to any but very small storms, and that groundwater movement within a phreatic aquifer was the dominant process at all times. The hydraulic gradient of the groundwater was considerably steeper than generally attributed to such systems. To aid in interpretation, numerical solutions of the Boussinesq equation were used cast in a coordinate system approximating that of the component catchments. These showed that the observations are explainable as the effect of catchment shape on groundwater outflow. The computations indicated a noted perturbation in recession hydrographs may be attributable to the presence of a symmetry boundary associated with the ridge.

A dynamical model for the overland flow on an infiltrating catchment

An approximate lumped parameter model for the surface runoff phenomenon on a catchment is presented. It consists of two submodels which are spatial discretizations of the basic partial differential equations of overland flow and infiltration. The aim of the model is to describe the dynamical input-output relationship between the rainfall rate and the surface runoff from the catchment. The boundary conditions of the infiltration process are modelled in an approximate way so that the number of state variables in the model can be reduced. With the aid of a single model parameter it is possible to describe simple catchment shapes like linearly converging and diverging surfaces. The model structure is flexible so that it can also be applied to more complex catchment configurations. The simulation results show that the phenomenon under consideration can be properly described by the model structure presented.

A derived flood frequency distribution using Horton Order Ratios

A flood frequency distribution is derived from assumed climatic distributions and the geomorphologic unit hydrograph (GUH) model of catchment response. The derived distribution is tested on two Appalachian Mountain catchments and shows good agreement with historical data. Because the GUH is rooted in catchment shape and geomorphology, this derived frequency distribution may be a promising vehicle for studying the effect of catchment shape on flood frequency characteristics. Furthermore, it is felt that the question of catchment homogeneity and similarity, necessary for regional flood estimation, can also be studied through the GUH derived flood distribution.

Sources of sediment-induced reductions in water quality appraised from catchment attributes and land use

Throughout the world, mountainous regions provide the principal sources of water supply. The usefulness of the water supply depends in part on the quality of the water, which is most often dependent on the sediment concentration. In periods of floods and from areas with unstable terrain, the sediment concentration may be naturally high. On the other hand, man's activities may create unstable areas and thereby decrease the quality of water from catchments. Catchments themselves give us the best means of determining both the natural and the man-accelerated sediment concentration of streamflow from mountain catchments. Suspended-sediment measurements from 61 catchments in California were used to relate suspended-sediment discharge to ten catchment attributes. Suspended sediment was normalized by using long-term streamflow of each catchment. Factor analysis showed no confounding among the ten attributes: regression on principal components gave an explained variance; land-use variable 30%; streamflow and rain-snow frequency 14%; geology, including faults, 11%; and tributary channel slope the other 3%. Catchment shape was the least important variable, with palm-shaped catchments having only 13% more sediment discharge than dendritic-shaped catchments. Differences in landslide classes produced the greatest differences in sediment discharge: sediment discharge from landslide class 6 was 12 times that from class 1. A separate analysis gave a basis for calculating landslide classes from catchment attributes. The use of results are illustrated in separating natural from accelerated sediment discharge and sediment concentration in the Redwood Creek Basin.