High Drainage Density Research Articles

A stochastic approach to modeling the role of rainfall variability in drainage basin evolution

We develop a simple stochastic theory for erosion and sediment transport, based on the Poisson pulse rainfall model, in order to analyze how variability in rainfall and runoff influences drainage basin evolution. Two cases are considered: sediment transport by runoff in rills and channels and particle detachment from bedrock or cohesive soils. Analytical and numerical results show that under some circumstances, rainfall variability can have an impact equal to or greater than that of mean rainfall amount. The predicted sensitivity to rainfall variability is greatest when (1) thresholds for runoff generation and/or particle detachment are significant and/or (2) erosion and transport are strong nonlinear functions of discharge. In general, sediment transport capacity is predicted to increase with increasing rainfall variability. Depending on the degree of nonlinearity, particle detachment capacity may either increase or decrease with increasing rainfall variability. These findings underscore the critical importance of hydrogeomorphic thresholds and other sources of nonlinearity in process dynamics. The morphologic consequences of rainfall variability are illustrated by incorporating the pulse rainfall theory into a landscape simulation model. The simulation results imply that, all else being equal, catchments experiencing a shift toward greater climate variability will tend to have (1) higher erosion rates, (2) higher drainage density (because of increased runoff erosion efficiency), and ultimately (3) reduced relief. The stochastic approach provides a useful method for incorporating physically meaningful climate data within the current generation of landscape evolution models.

The impact of the farming practice of remodelling hillslope topography on badland morphology and soil erosion processes

Badland landforms, created in Plio–Pleistocene clay landscapes of the Basilicata region of southern Italy, form marginal features in a semi-arid landscape dominated by the widespread cultivation of subsidised cereals. These badland features are high relative relief forms exhibiting a high drainage density and steep slopes, with slope angles typically in excess of 35°. Economic incentives to increase agricultural productivity have resulted in the practice of remodelling these marginal areas using heavy earth-moving equipment. Remodelling the badland features creates longer slopes at lower angles, which can be cultivated using conventional farm machinery. These changes in hillslope morphology have altered the degree to which soil erosion processes operating in these areas are spatially coupled. In the badland areas, erosion and deposition are strongly localised with minimal sediment delivery to ephemeral or perennial channel systems. The economically-driven change in land use from visually striking badland areas to newly remodelled fields for agricultural use results in an increase in the coupling of drainage networks and a net increase in soil erosion.

Integrated resource study for conservation and management of Ropar wetland ecosystem, Punjab

Integrated resource study in Ropar wetland ecosystem was undertaken to analyse physiography, drainage, landuse and vegetation status. Various thematic maps have been prepared using black and white aerial photographs on 1:20,000 scale and IRS 1A LISS-II (FCC) on 1:50,000 scale. The Ropar wetland ecosystem is comprised of six major landforms i.e. Siwalik hills, Valley, Piedmont plain, Alluvial plain, River terraces and River courses. The study area show high drainage density with sub dendritic and sub parallel drainage. The area has poor vegetative cover which results in extensive erosion and sedimentation of Ropar lake. The water spread and. qualitative turbidity level in the notified wetland area was also monitored. Anthropogenic pressure, industrial pollution, sedimentation, eutrophication, illegal fishing and flooding have been identified as major threats to the wetland. Keeping in view the threats to Ropar wetland, the conservation measures have been suggested.

Martian drainage densities

Drainage densities on Mars range from zero over large areas of volcanic plains to 0.3–0.5 km−1 locally on some volcanoes. These values refer to geologic units, not to drainage basins, as is normal for terrestrial drainage densities. The highest values are close to the lowest terrestrial values derived by similar techniques. Drainage densities were determined for every geologic unit portrayed on the 1:15,000,000 geologic map of Mars. Except for volcanoes the geologic unit with the highest drainage density is the dissected Noachian plains with a drainage density of 0.0074 km−1. The average drainage density for Noachian units is 0.0032 km−1, for Hesperian units is 0.00047 km−1, and for Amazonian units is 0.00007 km−1, excluding the volcanoes. These values are 2–3 orders of magnitude lower than typical terrestrial densities as determined by similar techniques from Landsat images. The low drainage densities, despite a cumulative record that spans billions of years, indicate that compared with the Earth, the channel‐forming processes have been very inefficient or have operated only rarely or that the surface is extremely permeable. The high drainage density on volcanoes is attributed to a local cause, such as hydrothermal activity, rather than to a global cause such as climate change.

Analyzing cumulative environmental effects of agricultural land drainage in southern Ontario, Canada

The temporal and spatial attributes of agricultural land drainage suggest that drainage is a potential source of cumulative environmental change. This paper applies a cumulative effects model of drainage to the case of southern Ontario, Canada. The application is focused on the cumulative effects of drainage on volume and timing of water flow, content of nitrate-nitrogen and atrazine residue in receiving channels, and area and distribution of wetlands. These are investigated using available information on drainage-environment interactions and geographic information system (GIS) technology. Available data show that the combined effect of two pathways of accumulation in drained areas (i.e. subsurface flow and runoff) increases the content of nitrate in water, but decreases the atrazine content, relative to the single pathway (i.e. runoff) in undrained areas. Drainage alters timing and volume of water flow at the field scale, but evidence of accumulation of these changes at the watershed scale is inconclusive for southern Ontario. This is attributed to counteractive processes and constraints of available data bases. Fragmentary effects are evident in the spatial association between drainage density and change in area and contiguity of wetlands at the subregional and regional scales. Application of GIS demonstrated that 47% of the decline in total wetland area (1312 ha) in Peel Township during 1800–1990 is attributable to subsurface drainage. Average patch size decreased nearly 50%, and the number of large patches (> 50 ha) declined by about 65%. In southern Ontario, counties with the greatest reduction in wetland area are consistently characterized by high drainage density. Collectively, the empirical application demonstrated the utility of the cumulative effects model, and showed that it is possible to conduct a cumulative effects analysis using available information sources.

Densidade de drenagem e sua relação com fatores geomorfopedológicos na área do alto rio Pardo, SP e MG

A densidade de drenagem é um dos principais parâmetros na análise morfométrica de bacias hidrográficas, correspondendo ao comprimento médio de canais de uma bacia por unidade de área. A distribuição espacial dos valores da densidade de drenagem na região do alto rio Pardo - situada entre a porção nordeste do Estado de São Paulo e sul de Minas Gerais - foi obtida a partir da medição de comprimentos de canais em celas quadráticas que recobriram toda área. Observou-se uma significativa correlação espacial das anomalias de alta densidade de drenagem com a distribuição das principais estruturas reativadas no Mesozóico-Cenozóico, sugerindo uma retomada erosiva das formas de relevo, devido à neotectônica. As principais anomalias de rarefação de drenagem foram observadas nos terrenos sedimentares da Bacia do Paraná. Uma menor correlação foi obtida com os solos, podendo-se observar uma tendência geral de concentração de zonas anômalas de alta densidade de drenagem nos solos podzólicos e baixa a intermediária nos latossolos. Os resultados indicam que o estudo desta variável morfométrica representa uma importante ferramenta na definição preliminar de áreas, nas quais se podem buscar evidências estruturais e tectônicas de campo com maior probabilidade de êxito.

Morphological characteristics of gully networks and their relationship to host materials, Baringo District, Kenya

The morphological characteristics of gully networks in Baringo District, Kenya are described in relation to host materials. All gullies studied were part of a well integrated network characterised by a high drainage density. Causes of network rejuvenation leading to gullying are postulated. The morphology of the individual gullies were found to be related to the most material. Gullies formed on weathered bedrock had a dendritic drainage network with convex slopes. The morphology of gullies developed in lacustrine sediments varied with sediment texture and chemistry. V-shaped dendritic gullies with a concave longitudinal profile were associated with a high clay content and high sodium content whereas entrenched gullies were associated with a high silt content and low sodium content. Process inferences are made in order to explain the variation in gully morphology.

On the extraction of channel networks from digital elevation data

AbstractChannel networks with artibtrary drainage density or resolution can be extracted from digital elevation data. However, for digital elevation data derived networks to be useful they have to be extracted at the correct length scale or drainage density. Here we suggest a criterion for determining the appropriate drainage density at which to extract networks from digital elevation data. The criterion is basically to extract the highest resolution (highest drainage density) network that satisfies scaling laws that have traditionally been found to hold for channel networks. Procedures that use this criterion are presented and tested on 21 digital elevation data sets well distributed throughout the U.S.

Nutrient loading and macrophyte growth in Wilson Inlet, a bar-built southwestern Australian estuary

Wilson Inlet is a ‘bar-built’ estuary, open to the ocean only when a sandbar has been breached after river flow. estimates are presented of phosphorus and nitrogen loadings from rivers, losses to the ocean, and amounts present in estuarine components during a particular year. Following bar opening, a volume of water equivalent to 35% of estuarine volume at the time was lost, providing a major loss of dissolved nutrients from the estuary. While the bar was open (51 days) water was displaced through river flow, but there was little tidal exchange. There was net retention of phosphorus (about 60% of river input) and some loss of nitrogen (less than 15%). Much of the nutrient held in the estuary was in surface sediments, but concentrations have shown little change with time and are similar to other southwestern estuaries. In contrast there have been massive increases in the biomass of Ruppia megacarpa Mason in recent years; this constitutes more than 90% of plant biomass. The nutrient bank in this plant is large compared to the water column, and amounts recycled through plant material greatly exceeded riverine loading in the year of the study. Tissue N concentrations were relatively high and constant, tissue P relatively low and seasonally variable, suggesting P limitation of plant biomass. Estimates of nutrient loading from streams showed relatively higher nutrient inputs from catchments cleared for agriculture. These are in higher rainfall areas, have high drainage densities, large proportions of sandy soils and are subjected to phosphatic fertilizer application.

Flood Flow Frequency by SCS-TR-20 Computer Program

The U.S. Soil Conservation Service Computer Program for Project Formulation—Hydrology reproduces the highest recorded flood hydrograph and estimates statistically reliable flood flows for the North Branch Kawkawlin River in Michigan. The Kawkawlin River consists of two major tributaries with entirely different watershed characteristics. The input data required for this program were collected from topographic maps and field visits. Log-Pearson Type III analysis of the recorded annual peak flows shows that the results of this model compare very well and appear entirely within the 90% confidence interval. Variability of the skew coefficient affected by a low outlier is shown. Flows at the gaging station are attenuated by a wide flood plain and do not represent flows at other locations. Flooding of the main river is dominated by the south branch due to the high drainage density and short travel distance. Other methods applicable for the region are also used for comparison.

A Model to Predict Mean Annual Watershed Discharge

A method was developed for the estimation of long term discharge characteristics of small watersheds. It was shown that, besides the annual precipitation and the annual mean temperature, other factors also influence the discharge. Two newly established watershed parameters were developed for improving the long term discharge prediction techniques. The first watershed parameter may be determined from a few years long discharge—precipitation—temperature record. It was shown that the second watershed parameter is related to the drainage density which reflects the soil texture. This study proves the expectation that the long term discharge is higher from watersheds having high drainage densities than the reverse, provided the other factors are identical. The consistent evaluation of the drainage density from aerial photographs requires the application of a system of conventions. The conventions were discussed in detail in the text.

Development of fine-textured landscape relief in temperate pluvial climates

Abstract In a temperate pluvial climate, under conditions that favour episodic or seasonal high run-off though the annual rainfall is moderate, fine-textured relief (with high drainage density) may develop rapidly (feral at first, to become subdued later) as a result of first-cycle dissection of tectonic slopes or redissection of slopes that have been smoothed by the activities of frost in a glacial age. Under similar temperate pluvial conditions such textures may, however, develop also, though probably more slowly, in landscapes that have long ago become fully mature and even subdued, including some that have been subject to slow downwasting of the surface during a state of dynamic equilibrium. This change to fine texture and high drainage density may be brought about by a change in rainfall characteristics to those favouring high run-off, either epiwdic or seasonal (though a similar change may be attributable in some regions to the more pluvial conditions wming on in glacial ages). The reverse change, t...