Spatial-temporal assessment of water and sediment connectivity through a modified connectivity index in a subtropical mountainous catchment

It is well known that in-stream large wood (LW) can have significant effects on channel hydraulics and thus water and sediment connectivity, i.e. by creating hydraulic resistance that decreases flow velocity and transport capacity. The relationship between an in-stream LW structure and its hydraulic function (incl. the related effects on water and sediment connectivity) is generally quantified through drag force. Drag analyses, however, are data-demanding and often not straightforward - especially in complex debris jam settings where LW accumulations consist of wood pieces of widely variable sizes. Here, we introduce a simple LW dis-connectivity index (calculated based on visually estimated, field-derived LW parameters such as the degree of channel blockage), which has been applied in different sediment management contexts in medium-sized mixed-load streams in Austria.&#160;

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Development and application of a sediment connectivity index to small fluvial catchments: a case study in Arenoso stream, Córdoba, Argentina

Environmental Earth Sciences ◽

10.1007/s12665-021-09585-8 ◽

2021 ◽

Vol 80 (8) ◽

Author(s):

María Jimena Andreazzini ◽

Susana Beatriz Degiovanni ◽

María Eugenia Benito ◽

Karina Vanesa Echevarria

Keyword(s):

Connectivity Index ◽

Sediment Connectivity

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Mapping water and sediment connectivity

The Science of The Total Environment ◽

10.1016/j.scitotenv.2019.04.071 ◽

2019 ◽

Vol 673 ◽

pp. 763-767 ◽

Cited By ~ 9

Author(s):

Marco Cavalli ◽

Damià Vericat ◽

Paulo Pereira

Keyword(s):

Water And Sediment ◽

Sediment Connectivity

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Effect of ecological construction on sediment connectivity in a typical small watershed on Loess Plateau

10.5194/egusphere-egu21-13758 ◽

2021 ◽

Author(s):

Yongyong Ma ◽

Zhanbin Li ◽

Jingming Hou ◽

Peng Li ◽

Zongping Ren ◽

...

Keyword(s):

Soil Erosion ◽

Loess Plateau ◽

Yellow River ◽

The Yellow River ◽

Small Watershed ◽

Water And Sediment ◽

Local Soil ◽

Sediment Connectivity ◽

The Mean ◽

Ecological Construction

In recent years, the significantly decrease of water and sediment in the Yellow River has attracted wide attention from domestic and foreign scholars. The Loess Plateau is the main source of sediment in the Yellow River, which ecological environment changes caused by large-scale ecological construction measures is considered as one of the main factors affecting the water and sediment changes in the Yellow River. In this study, the Wangmaogou small watershed in Loess Plateau was taken as the study area. On the basis of summing up the process of ecological construction in Wangmaogou watershed, and restoring the topography before ecological construction by topographic map, we set up four scenarios of ecological construction to analyzed the characteristics of sediment connectivity under different ecological construction scenarios and the effects of ecological construction on sediment connectivity, which are before ecological construction, only slope measures are built, only channel measures are constructed, and at the same time slope measures and channel measures are constructed. Under the same ecological construction scenario, the index of sediment connectivity (IC) of the basin shows a decreasing trend from ridge to gully, which mean the connectivity of the sediment at the ridge is less than that at the gully, and the gully are more prone to occur soil erosion than ridge. The distributed of large amount of construction land in the middle and lower reaches at the main gully of Wangmaogou small watershed reduces the connectivity of their surrounding sediment, and the region is prone to occur sediment deposition. Eco-construction measures have decreased significantly the sediment connectivity index (p<0.01) of Wangmaogou small watershed, and reduced the occurrence of soil erosion. Laying ecological measures lessened the possibility of local soil erosion, and increased the resistance of sediment in the transport process. Compared with the situation without ecological control, the mean of Dup index decreased by 75.27% by laying slope and gully measures, while the mean of Dup index decreased by only 6.45% by laying gully measures.

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Impedance influence on the index of sediment connectivity in a forested mountainous catchment

Geomorphology ◽

10.1016/j.geomorph.2019.106962 ◽

2020 ◽

Vol 351 ◽

pp. 106962 ◽

Cited By ~ 1

Author(s):

Franciele Zanandrea ◽

Gean Paulo Michel ◽

Masato Kobiyama

Keyword(s):

Mountainous Catchment ◽

Sediment Connectivity

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What do models tell us about water and sediment connectivity?

Geomorphology ◽

10.1016/j.geomorph.2020.107300 ◽

2020 ◽

Vol 367 ◽

pp. 107300 ◽

Cited By ~ 1

Author(s):

Jantiene E.M. Baartman ◽

João Pedro Nunes ◽

Rens Masselink ◽

Frédéric Darboux ◽

Charles Bielders ◽

...

Keyword(s):

Water And Sediment ◽

Sediment Connectivity

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Sediment connectivity in the Koiyavgan glacier's cirques (Adyl-Su river basin, Caucasus, Russia)

10.5194/egusphere-egu21-16175 ◽

2021 ◽

Author(s):

Andrei Kedich ◽

Maxim Uspensky ◽

Anatoly Tsyplenkov ◽

Sergey Kharchenko ◽

Valentin Golosov

Keyword(s):

River Basin ◽

Area Coverage ◽

Connectivity Index ◽

Bottom Surface ◽

Top Down ◽

Dem Resolution ◽

Flow Accumulation ◽

Roughness Index ◽

Sediment Flow ◽

Sediment Connectivity

The highland cirques mostly created by nivation and glacial exaration take large areas in mountains and have a significant role in the sediment transit of the basins. The approximate view on the connection of cirques and low levels in the sediment flow could be given with the sediment connectivity index analysis. We study the spatial distribution of the index for typical ice cirque &#8211; the Koiyavgan cirque near the join of the Main Caucasus Range and its offshoot (the Gumachy range). This area is located in the tops of the Adyl-Su valley (left side of the Baksan river basin). In August 2020, we got a high-resolution orthophoto image (13+ cm) and digital elevation model (27+ cm) from aerial photography. The territory located in the elevation range from 3230 to 4022 m. Geological conditions: gneiss, metamorphic shale and basic dark coloured igneous rocks. There is no developed vegetation cover. Typical post-glacial cirques topography includes (top-down): mountain tops, very steep bedrock slopes, colluvial footslopes and fans, cirques bottom (moraine ridges with dividing valleys, craters from melting of the in-moraine covered ice etc.) with fluvial, avalanche and creep post-shaping, and bottom surface break as analogue of riegels in glacial trough valleys. The connectivity index (CI) after Cavalli et al. [2013] is very dependent on initial DEM resolution, from the method for filling mistaken depressions, from window size for computing intermediate geomorphometric variables (e.g. roughness index), from choice in flow impedance variable, from area coverage and terrain diversity and others. We compute connectivity index with the parameters: 1) DEM resolution &#8211; 27 cm; 2) impedance variable &#8211; terrain roughness index (standard deviation of elevation) with window 7*7 cells; 3) standard filling method used in the ArcMap (filling local depression without any limitations on maximum depth); 4) range of impedance values before normalization (partially related to area coverage) is from 0 to 72 m. In the some buffers from the channel network the connectivity index generally grows in the top-down direction. Greatest spurt of the CI values relates to the cirques low border - the riegel (3300 m asl). There are two levels characterised with low values of the CI: 3550 m and 3750 m. The first one is backside of cirques bottom with relatively low flow accumulation area and low-moderate slopes (0-25&#176;), the second one is mountain tops with high steep slopes, but with lowest flow accumulation. For different geomorphodynamical zones the threshold of IC where sediment transit turns into sediment accumulation has differ values: for example, -2.3 for colluvial fans and -2.5 for alluvial fans (p-value for differences significance &#171; 0.01). Maximum values of CI (quantile: the top-95%) for accumulative positions again are -1.27 and -0.72. Its means, those accumulative processes areas with different mechanics of the deposition may be delineated with using non-constant CI values only. The potential of sediment flow connectivity modelling for high mountain isn&#8217;t exhausted, but its application needs wide discussion and calibration. The study was supported by the Russian Science Foundation (project No. 19-17-00181).

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