Variations in sediment sources and yields in the Finger Lakes and Catskills regions of New York

The proportional contributions of stream bank and surface sources to fine sediment loads in watersheds in New York State were quantified with uncertainty analysis. Eroding streamside glacial drift, including glaciolacustrine deposits, were examined to help explain variations in the proportional contributions made by bank erosion. Sediment sources were quantified by comparing concentrations of the bomb‐derived radionuclide ¹³⁷Cs in fluvial sediment with sediment from potential source areas such as agricultural soils, forest soils and stream banks. To compare sediment sources in streams containing abundant deposits of fine‐grained glacial drift with watersheds that lacked moderate or extensive streamside deposits, samples were taken from 15 watersheds in the region. The mean contribution of bank erosion to sediment loads in the six streams with glaciolacustrine deposits was 60% (range 46–76%). The proportional contribution of bank erosion was also important in one stream lacking glaciolacustrine deposits (57%) but was less important in the remainder, with contributions ranging from 0 to 46%. Data from this study on the varying contributions of bank erosion and data from past studies of sediment yield in 15 watersheds of New York State suggest that eroding streamside glacial deposits dominate sediment yield in many watersheds. In other watersheds, past impacts to streams, such as channelization, have also resulted in high levels of bank erosion. Copyright © 2007 John Wiley & Sons, Ltd.     

Distributed discharge and sediment concentration predictions in the sub‐humid Ethiopian highlands: the Debre Mawi watershed

Experimental research in the Ethiopian highlands found that saturation excess induced runoff and erosion are common in the sub‐humid conditions. Because most erosion simulation models applied in the highlands are based on infiltration excess, we, as an alternative, developed the Parameter Efficient Distributed (PED) model, which can simulate water and sediment fluxes in landscapes with saturation excess runoff. The PED model has previously only been tested at the outlet of a watershed and not for distributed runoff and sediment concentration within the watershed. In this study, we compare the distributed storm runoff and sediment concentration of the PED model against collected data in the 95‐ha Debre Mawi watershed and three of its nested sub‐watersheds for the 2010 and 2011 rainy seasons. In the PED model framework, the hydrology of the watershed is divided between infiltrating and runoff zones, with erosion only taking place from two surface runoff zones. Daily storm runoff and sediment concentration values, ranging from 0.5 to over 30 mm and from 0.1 to 35 g l^?1, respectively, were well simulated. The Nash Sutcliffe efficiency values for the daily storm runoff for outlet and sub‐watersheds ranged from 0.66 to 0.82, and the Nash–Sutcliffe efficiency for daily sediment concentrations were greater than 0.78. Furthermore, the model uses realistic fractional areas for surface and subsurface flow contributions, for example between saturated areas (15%), degraded areas (30%) and permeable areas (55%) at the main outlet, while close similarity was found for the remaining hydrology and erosion parameter values. One exception occurred for the distinctly greater transport limited parameter at the actively gullying lower part of the watershed. The results suggest that the model based on saturation excess provides a good representation of the observed spatially distributed runoff and sediment concentrations within a watershed by modelling the bottom lands (as opposed to the uplands) as the dominant contributor of the runoff and sediment load. Copyright © 2014 John Wiley & Sons, Ltd.     

Evolution of scouring process downstream of grade‐control structures under steady and unsteady flows

For many incised channels, one of the most common strategies is to install some hard structures, such as grade‐control structures (GCSs), in the riverbed to resist further incision. In this study, a series of experiments, including both steady and unsteady flow conditions, were conducted to investigate the scouring process downstream of a GCS. Three distinct phases, including the initial, developing and equilibrium phases, during the evolution of scour holes were identified. In addition, a semi‐empirical method was proposed to predict the equilibrium scour‐hole profile for the scour countermeasure design. In general, the comparisons between the experimental and simulated results are reasonably consistent. As the studies on temporal variation of the scour depth at GCSs caused by floods are limited, the effect of flood hydrograph shapes on the scour downstream of GCSs without upstream sediment supply was also investigated experimentally in this study. Based on the dimensional analysis and the concept of superposition, a methodology is proposed to simulate the time evolution of the maximum scour depth downstream of a GCS for steady flows. Moreover, the proposed scheme predicts reasonably well the temporal variations of the maximum scour depth for unsteady flows with both single and multiple peak. Copyright © 2012 John Wiley & Sons, Ltd.     

Modelling the impacts of subsurface drainage on surface runoff and sediment yield in the Le Sueur Watershed,Minnesota, USA

Abstract

Tile drainage influences infiltration and surface runoff and is thus an important factor in the erosion process. Tile drainage reduces surface runoff, but questions abound on its influence on sediment transport through its dense network and into the stream network. The impact of subsurface tiling on upland erosion rates in the Le Sueur River watershed, USA, was assessed using the Water Erosion Prediction Project (WEPP) model. Six different scenarios of tile drainage with varying drainage coefficient and management type (no till and autumn mulch-till) were evaluated. The mean annual surface runoff depth, soil loss rate and sediment delivery ratio (SDR) for croplands, based on a 30-year simulation for the watershed with untiled autumn mulch-till (Scenario 1), were estimated to be 83.5 mm, 0.27 kg/m² and 86.7%, respectively; on no-till management systems (Scenario 4), the respective results were 72.3 mm, 0.06 kg/m² and 88.2%. Tile drains reduced surface runoff, soil loss and SDR estimates for Scenario 1 by, on average, 14.5, 8.1 and 7.9%, respectively; and for Scenario 4 by an estimated 31.5, 22.1 and 20.2%, respectively. The impact of tile drains on surface runoff, soil loss and SDR was greater under the no-till management system than under the autumn mulch-till management system. Comparison of WEPP outputs with those of the Soil Water Assessment Tool (SWAT) showed differences between the two methods.

Editor Z.W. Kundzewicz

Citation Maalim, F.K. and Melesse. A.M., 2013. Modelling impacts of subsurface drainage on surface runoff and sediment yield in the Le Sueur Watershed in Minnesota, USA. Hydrological Sciences Journal, 58 (3), 570–586.     

Modelling the advance–retreat cycle of a tidewater glacier with simple sediment dynamics

We present a simple coupled glacier-sediment model to simulate the evolution of a tidewater glacier. The model is based on a consideration of the total mass budget of a glacier, whereas ice mechanics are fully parameterized. The calving rate at the glacier terminus is assumed to be proportional to the water depth. We show that the formation of a morainic shoal has a profound influence on the response of a tidewater glacier to climatic forcing. For a slow periodic forcing of the equilibrium-line altitude, the model glacier advances steadily into the estuary, builds up a submarine terminal moraine, and then retreats rapidly when a critical point is hit. For a slowly increasing equilibrium-line altitude, at a rate as low as 1 m per 5 years, we find terminus retreat rates of up to 10 km in 50 years. Our model suggests that, although the response of tidewater glaciers to external forcing is strongly nonlinear, the onset of retreat is controlled by climate change.     

Paraglacial response of steep,sediment‐mantled slopes to post‐‘Little Ice Age’ glacier recession in the central Swiss Alps

This research assesses the morphological consequences of recent (post‐‘Little Ice Age’) paraglacial reworking of valley‐side sediment mantles in the European Alps. It aims to identify the extent and conditioning factors of slope adjustment at sites in the Swiss Alps, model the temporal pattern, and assess the rates of sediment reworking involved. Gully systems have cut into steep, high‐level lateral moraines, and debris cones have accumulated downslope. Debris flow is the dominant agent of sediment transfer. Factors controlling the extent of this activity include moraine slope gradient, relief and moisture availability. Gullies appear to have reached their maximum dimensions within ca. 50 yr of deglaciation, after which gully relief is reduced by removal of inter‐gully slopes and gully infilling (within 80–140 yr). On the most recently deglaciated terrain, minimum erosion rates average ca. 95 mm yr^?1 since gully initiation, greatly exceeding ‘normal’ erosion rates in other environments. Mean annual accumulation of a single debris cone since ice retreat was calculated to be ca. 30 mm yr^?1. Implications of these findings are applied to patterns of paraglacial sediment‐mantled slope adjustment, conceptualising paraglacial landscape response in terms of a sediment release exhaustion model, and paraglacial landform succession. Copyright © 2005 John Wiley & Sons, Ltd.     

Geochemical evidence (C,N and Pb isotopes) of recent anthropogenic impact in south‐central Chile from two environmentally distinct lake sediment records

In this paper, we compare the elemental and isotopic (C, N, Pb) geochemistry of lake sediments from two contrasted environments in south‐central Chile. The first lake, Laguna Chica de San Pedro (LCSP), is situated in the urbanised area of the Biobio Region (36°S). The second lake, Lago Puyehue (40° S), is located 400 km to the southeast of LCSP and within an Andean national park. Our aim is to identify environmental impacts associated with increasing industrial activities and land degradation during the last 150 a. In LCSP, shifts in C/N atomic ratios, δ¹³C and δ¹⁵N from 1915–1937 to the late 1980s are attributed to successive land degradation episodes in the lake watershed. Based on a Pb isotopic mixing model, we estimate that up to 20% of lead in LCSP sediments is supplied from urban atmospheric pollution. By contrast, human impact in the watershed of Lago Puyehue is very limited. We observe no change in organic geochemistry during the last 150 a and lead contamination remains lower than 5%, even during the last decades. Although contamination levels are much higher in LCSP than in Lago Puyehue, a peak in anthropogenic Pb is recorded during the same period (1974–1976) at both sites. This maximum contamination level is consistent with increased industrial activity in the vicinity of Concepción. Copyright © 2010 John Wiley & Sons, Ltd.     

TRANSFERABLE PHOSPHORUS IN SEDIMENTS OF THE HUANGHE RIVER ESTUARY ＇S ADJACENT WATERS

Based on a new idea for research on cycling of marine biogenic elements, this study showed that only the leachable form phosphorus in natural grain sizes manne sediments constitutes the transferable phosphorous in the sediments. The transferable phosphorus content in the natural grain sizes surface sediments in the Huanghe River estuary adjacent waters ranges from 58.5-69.8 μg/g, accounting for only 9.1%-11.0% of the total phosphorus content, whereas the leachable form (“transferable” )phosphorus content in the sediment after it was totally ground into powder was found to be 454.8-529.2μg/g, accounting for 73.4%-89.1% of the total phosphorus. Analysis of the correlation between thebill,ass of benthos and the leachable form (“transferable” ) phosphorus showed that most of the leachableform (“transferable”) phosphorus in the totally ground sediment did not participate in the marine biogeo chemical cycling. Furthermore, a synchronous survey on benthos showed that the biornass of meio-and maero-benthos exhibited good positive correlation with the leachable form of phosphorus in the naturalgrain sizes sediment, but peorer correlation with the leachable form (“transferable”) phosphorus in the totally ground sediment, indicating that transferable phosphorus in marine sediment is the leachable form of phosphorus in the natural grain sizes sediments, and is not the previously known leachable form(“transferable”) phosphorus obtained from the totally ground sediment.     

ESR DATING OF FLUVIAL SEDIMENTS USING GE CENTER IN QUARTZ

Using the Ge centers of quartz sediments, the buried ages of fluvial sediments were determined by ESR technique. The ESR ages obtained from Ge centers are consistent with the TL ages, correspond with their horizons, accord with the geological background, and every ESR age is available. In this paper, determination of total dose of natural radiation (TD) and the reliability of ESR age using Ge center are also discussed.