Quantification of biogeomorphic interactions between small-scale sediment transport and primary vegetation succession on proglacial slopes of the Gepatschferner, Austria

<p>Proglacial slopes provide suitable conditions to observe the co-development of abiotic and biotic systems. The frequency and magnitude of geomorphic processes and composition of plants govern this interplay, which is described in the biogeormorphic feedback window for glacier forelands. The study sets out to quantify small-scale sediment transport via mechanical erosion plots along a plant cover gradient and to investigate the multidirectional interactions between abiotic and biotic processes. We aim to generate quantitative data to test the biogeomorphic feedback window.</p><p>Small-scale biogeomorphic interactions were investigated on 30 test plots of 2 x 3 m size on proglacial slopes of the Gepatschferner (Kaunertal) in the Austrian Alps during snow-free summer months over three consecutive years. The experimental plots were established on slopes along a plant cover gradient. A detailed vegetation survey was carried out to capture biotic conditions and specific sediment yield was measured at each plot. Species abundance and composition at each site, as well as plant functional types reflected successional stages.</p><p>We observed a strong decline in geomorphic activity on plots with above 30% plant cover. Mean monthly rates of specific sediment yield decreased from 111 g m<sup>-2 </sup>to 37 g m<sup>-2</sup>. Non-metric multidimensional scaling showed distinct vegetation composition for the three stages of biogeomorphic succession. Quantified process rates and observed vegetation composition support the concept of biogeomorphic feedback windows. The findings help to narrow down a stage during succession where the importance of biotic processes start to dominate.</p>

Geomorphometric properties and variability of sediment delivery ratio and specific sediment yield among sub-basins of the Karra River, Hetauda, central Nepal Sub-Himalaya

Geomorphometric properties of watershed-scale are often calculated to characterize drainage basins morphology for evaluating their geomorphic status of basin development. More recently these properties have widely been applied in inferring the sediment delivery ratio and sediment yields of the basin to estimate and know sediment erosion status of drainage basin with the help of morph metric data. In fact, sediment delivery ratio (SDR) and specific sediment yield (SSY) of the basins depend not only on watershed properties but also indirectly on other factors such as climate, hydrology, land use and geology, which can be of low variation for a small watershed. The aims of the present study were to compute some of the geomorphometric parameters of the Karra River Basin (KRB), located in Hetauda, Makawanpur District, Central Nepal, to compare some of these among the sub-basins with varying geology, touse some of parameters in estimating sub-basin-wide SDR and SSY using empirical equations and to infer geomorphic development and erosion status of the basin. Based on hypsometric analysis, the southern sub-basins with mainly gravelly terrain are mostly of mature to unstable phase, whereas the northern sub-basins with bedrocks of the Lower and the Middle Siwalik Subgroups are of Monadnock phase to mature stage of basin development. Sediment delivery ratio (SDR) and specific sediment yield (SSY) estimated for the southern sub-basins of the KRB are relatively lower compared to those estimated for the northern sub-basins. Considering the geology of the KRB and hypsometric integral, although the SDR and SSY of the southern sub-basins are lower compared to the northern sub-basins, the southern sub-basins are vulnerable to erosion because of their unstable geomorphic development stage and pervasive distribution of unconsolidated weak sediments having high erodibility.

A global perspective on denudation data, primarily specific sediment yield in mountainous regions

A brief review of the evolution of denudation research since the 1960s is followed by a review of specific sediment yield variability in mountainous regions of the world as a function of spatial scale, relief, glaciation, lithology and disturbance type and location within the basin. A general model of scalar relations of suspended sediment yield for Canadian regions warns against comparing data from basins with areas ranging over several orders of magnitude. A regional summary of specific sediment yield in mountainous British Columbia confirms that in basins <1 km2 and >30,000 km2 specific sediment yield decreases with basin size whereas in basins of intermediate size (between 1 km² and 30,000 km²) specific sediment yield increases with basin size. This effect is interpreted in terms of three distinct process zones in every mountain basin. These zones can be characterized as a) generally degrading hillslope zones, b) generally aggrading footslopes and valley sides, and c) channelized flows on valley floors demonstrating either net aggradation or degradation. These are identifiable repeating elements in such landscapes. Suspended sediment yield data from mountainous regions around the world are considered in light of the British Columbia model. Some support for the model is found where basins are stratified according to scale, relief, lithology, disturbance types, and location within each basin. Disturbance types include the presence of glaciers, land use activities of various kinds, such as increasing population pressure in the intertropical montane zone, changing population distribution and associated economic activities in the temperate montane zone, and potentially hydroclimate change.

DISCHARGE LIQUID, VECTOR OF TOTAL SUSPENDED SEDIMENT (TSS) OF MAYO TSANAGA AT MAROUA (FAR NORTH CAMEROON)

Mayo Tsanaga is the Cameroonian part of the Lake Chad Basin ungauged. The knowledge of discharge is essential for the design of hydraulic structures and for hydrological risk prediction. The objective of this study is to evaluate discharge, total suspended sediment and the deduction of the specific sediment yield. The exploration of velocity fields and the differences in the pre and post filtration filter weights were adopted as a methodology. The results revealed that annual discharges of Mayo Tsanaga at Maroua from 2012 to 2014 are respectively 1.94 ± 0.38 m3 /s, 2.18 ± 0.43 m3/s and 0.89 ± 0.17 m3/s. Mayo Tsanaga discharge will be used when sizing the second bridge on this river. Mayo Tsanaga's daily mean concentrations of TSS are respectively 429.384 mg/L ± 12.88 for the year 2013 and 17.45 ± 0.52 mg/L for the year 2014. The corresponding specific sediment yield (SSY) of Mayo Tsanaga are 34.92 t.km-2.year-1 in 2013 and 0.57 t.km-2.year-1 in 2014. The SSY expresses the amount of ground lowering for the whole catchment.

Comparison of different targeting methods for watershed management practices implementation in Taleghan dam watershed, Iran

Soil erosion and sediment control is important in watersheds with planned dam construction. For an efficient implementation of watershed management practices, identification of critical areas is vital. Many studies have made an effort to identify and prioritize critical sub-watersheds. But very limited studies have been conducted to rank sub-watersheds in terms of their sediment yield contribution at the watershed outlet. Therefore, the goal of this study is spatial priority of critical sources areas in Taleghan dam watershed based on three methods: (1) SSY-S: specific sediment yield at sub-watershed outlet (sediment yield/area), (2) SY-W: sub-watershed contribution to the sediment yield of the main watershed outlet/reservoir, and (3) SSY-W: specific sediment yield contribution of sub-watershed to the main watershed outlet/reservoir. The results of sub-watershed and prioritization showed that sub-watershed 22 has the highest sediment yield at its own sub-watershed outlet and main outlet of watershed. Also, implementing conservation practices in a high priority area shows a decrease in sediment yield at watershed outlet. However, sediment yield at outlet of watershed decreased about 11%, 15% and 17% from baseline scenario in methods 1, 2 and 3, respectively. The results show that the SSY-W method was more effective at reducing sediments entering the reservoir of Taleghan dam.

Evaluation of sediment production and siltation in a small earth dam in Fernandópolis, SP

The siltation is a natural process, but can be accelerated by human actions and results in major problems for the reservoirs, reducing its useful volume for irrigation. An example of this problem was the reduction of the area of mirror water of Fernandópolis municipal dam in 48.3% during 20 years. Therefore, this study aimed to evaluate the production of sediments and siltation of Fernandópolis municipal dam from a methodology that can be applied to small earth dams for agricultural purposes. For this, it was monitored, monthly throughout the year, the volume of sediment deposited in the reservoir. The percentage of retention sediment in Fernandópolis municipal dam ranged from 53.9 to 94.5%, that associated with a high specific sediment yield, will cause its full silting in at most 57 years. It is recommended to minimize this process the restoration of permanent preservation areas and the removal of 17,500 m³ of sediment from the riverbed of the dam.