The world’s cryospheric regions, ranging from high mountains to polar regions, have experienced unprecedented atmospheric warming, glacier melting and permafrost thawing since the mid-20th century. This rapid cryosphere degradation has dramatically altered terrestrial/coastal landscapes, characterized by creating debuttressed valleys and thermokarst hillslopes, expanding unstable landscapes, and increasing the access to sub-/pro-glacially stored sediment. Such rapid landscape changes have resulted in increases in erosion and sediment loads, posing threats to riverine and near-shore marine environments and triggering cascading impacts on water-food-energy securities which support the livelihoods of a quarter of the global population.

Here, we present a global inventory of cryosphere degradation-driven increases in erosion and sediment yield, including 76 locations from the high Arctic, European mountains, High Mountain Asia and Andes, and 18 Arctic permafrost-coastal sites, collected from over 80 publications. This inventory confirms the widespread increase in sediment transport from cold regions in response to modern deglaciation. Moreover, we identify two to eight-fold increases in sediment fluxes and more than doubled coastal erosion rates in many cold regions between the 1950s and 2010s.

Such increases in sediment evacuation from deglaciating/thermokarst regions have been blamed for introducing large amounts of carbon, nitrogen, and pollutants into aquatic ecosystems, impacting primary productivity, river biodiversity, and water quality. In high-mountain areas, increased sediment fluxes have also hampered hydropower exploitation through reservoir sedimentation and turbine abrasion. Meanwhile, accelerated erosion along ice-rich Arctic permafrost coasts has caused an irreversible land loss, costing billions of dollars for relocating or protecting coastal infrastructure.

With continuous cryosphere degradation, sediment fluxes are likely to increase in the next decades until reaching a maximum (“Peak Sediment”). Theoretically, the timing of peak sediment can lag decades to hundreds of years behind the peak meltwater due to the remobilization of paraglacial and subglacial sediment legacy. Thereafter, sediment fluxes will decline as glacier/permafrost erosion ceases and active sediment contributing area shrinks. We predict that sediment-transport regimes will shift through three stages, from the ongoing temperature-dominated regime to a temperature-precipitation jointly controlled regime, eventually shifting toward a rainfall-dominated regime roughly between 2100-2200.

However, the understanding of sediment dynamics in cold regions is still limited by the lack of long-term observations and the inherent complexity of geomorphic processes, such as episodic events, scale/threshold effects in sediment transport, and positive/negative feedbacks of geomorphic responses. To underpin the forward-looking mitigation strategies for climate-sensitive and fragile cold regions, we call for the enhancement of multi-source sediment monitoring programs, fully distributed physics-based sediment-yield models, and interdisciplinary-international scientific collaborations.

How to cite: Zhang, T., East, A., Walling, D., Lane, S., Overeem, I., Koppes, M., and Lu, X.: Warming-driven erosion and sediment transport in the world’s cold regions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1498, https://doi.org/10.5194/egusphere-egu23-1498, 2023.

The relative proportion of bedload and suspended sediment transport in rivers features very large variations both in space (within and among rivers) and in time (ordinary vs infrequent floods). However, the current knowledge about the temporal variability in bedload/suspended proportion is limited, as well as of its controlling factors (e.g., water runoff, sediment supply). The present work investigates the partitioning of sediment load into bedload and suspended fractions in the glacier-fed Sulden/Solda River (eastern Italian Alps, drainage area 130 km²), where a monitoring station for water and sediment transport has been operating since 2014.

From 2014 to 2020 the station was equipped with one turbidimeter and 8 geophone plates for monitoring suspended sediment and bedload transport, respectively. Calibration curves for deriving suspended sediment concentrations were derived based on 474 water samples, whereas to convert the geophones signal to bedload mass a portable trap mounted on a crane was used (76 samples collected). Two meteorological stations located at about 2800 m and 1900 m a.s.l. recorded precipitation and air temperature within the catchment.

A 10-minute interval dataset was established, including suspended load, bedload, water discharge, precipitation, and air temperature, measured from May to October 2014-2020 (2018 data had to be excluded for technical problems of the turbidimeter). Hourly intervals characterised by data gaps regarding geophone plates or turbidimeter were excluded from the analysis, and a total of 18,549 hourly data were analysed. The overall range of water discharge observed in the study period was 0.7 – 80.8 m³/s, but reliable suspended sediment data are available only up to about 40 m³/s (RI about 2 yr). The mean annual discharge of the Sulden River was 6.3 m³/s, while the mean discharge from May to October equalled 10.0 m³/s.  

Results show that suspended/bedload partitioning varied with water discharge and time of the year (month) in a complex way. On average, the relative contribution of suspended sediment transport was around 89% for Q<10 m³/s, 96% with 10<Q<20 m³/s, and 97% for Q>20 m³/s. At the lower water discharges (Q<10 m³/s), the suspended sediment fraction diminished over the summer from May/June/July (about 94%) to August/September (88%), and reached its minimum value in October (79%). This trend is possibly due to the intense glacier ablation occurring in August, which increased the coarse sediment supply – transported as bedload in the channels – more markedly than the finer fractions carried in suspension.

At higher flow rates (Q>10 m³/s), the percentage of sediments transported in suspension shows an opposite temporal trend, increasing from May (80%) to October (97%). Such a remarkable difference compared to lower discharges may be due to the strong increase in suspended sediment concentration at higher water discharges multiplied by larger water volumes carrying suspended transport through the entire flow depth, differently from bedload. Such complex dynamics is consistent with previous results in the Sulden River, where a low effective discharge for bedload – driven by the supply of coarse sediments during the glacier melt period – was observed for the same period analysed here.

How to cite: Bonfrisco, M., Coviello, V., Engel, M., Nadalet, R., Dinale, R., and Comiti, F.: Temporal variability of bedload vs suspended sediment load in a glacier-fed Alpine river, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11308, https://doi.org/10.5194/egusphere-egu23-11308, 2023.

Earthflows occur throughout New Zealand’s soft-rock hill country and may play an important role in catchment sediment dynamics and related water quality issues by providing a persistent source of sediment to the channel network. However, earthflows are not well accounted for in catchment sediment models. A better understanding of their drivers, movement dynamics, and sediment load contributions is needed to improve existing models, and to forecast their trajectories under projected climate change.

We present findings from four years of monitoring an 80,000 m² earthflow in the Haunui research catchment, New Zealand. A range of complementary proximal sensing technologies have been deployed to provide data on sub-daily to multi-year movement rates, and annual volumetric change. A continuously operating GNSS receiver (cGNSS), located in the toe of the earthflow, records at 30-second intervals and is differentially corrected against a nearby reference station to produce centimetre-scale measurements of toe movement. Piezometers have been installed to provide a continuous timeseries of pore water pressure near the failure surface, and are complemented by continuous meteorological and stream flow data from a nearby monitoring station, allowing phases of earthflow movement to be linked with hydrological drivers. The high-frequency data are supplemented by a network of ~30 monitoring pegs distributed across the earthflow and routinely surveyed with rtk-dGNSS to provide a spatial representation of annual movement rates. Repeat UAV-based Structure-from-Motion (SfM) surveys provide high-resolution annual measurements of volumetric change via morphological budgeting.

We present insights into the movement dynamics and sediment load contribution of the earthflow across a range of hydrological conditions, from summer low flows to storm events. Movement rates up to 0.25 m day^-1and 7.5 m yr^-1 have been recorded, with average annual movement rates of 4-6 m across the earthflow. Phases of movement have coincided with seasonal fluctuations in groundwater levels, with continuous movement occurring from June to November (winter and spring) when groundwater levels remain elevated. Accelerations in movement during these months are associated with periods of higher magnitude rainfall and stream flow. Cessation of movement occurs as the earthflow body begins to dry in December, and the earthflow remains mostly stable until June when groundwater levels become elevated again.

Morphological budgeting has revealed erosion in the earthflow head has been largely offset by deposition in the toe, with gross volumetric change of 34,000 m³ and net change of 4,000 m³. The estimated annual sediment contribution to the stream network has varied from 4% to 32% of the catchment sediment load. These data indicate groundwater level is an important parameter for modelling earthflow dynamics, and may be critical in forecasting earthflow response to climate change. Cycles of deposition and erosion of material at the earthflow-channel interface complicate the link between on-slope phases of movement and contribution to stream sediment loads. Simple box models may therefore inadequately represent sediment delivery from earthflows over shorter timescales.

How to cite: Neverman, A., Smith, H., Vale, S., and Betts, H.: Understanding drivers of earthflow dynamics and sediment delivery, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1273, https://doi.org/10.5194/egusphere-egu23-1273, 2023.

Extensive agriculture and mining practices increase erosion and sediment transport leading to natural disasters, such as flash floods, landslides and water quality degradation. This is especially evident in areas with high and episodic rainfalls and lousy land use and agricultural management, such as the Lake Kivu region in the eastern Democratic Republic of the Congo (DRC). Due to the growing population and the need to increase crop productivity in the region, poor agriculture practices combined with unmonitored mining lead to severe soil degradation increasing erosion rates and sediment and nutrient export to the surrounding water bodies. In this regard, the Kivu Lake area has experienced an increase in sediment export rates of various orders of magnitude in the last ten years without an obvious triggering factor. This increase is noticeable by the vast growth in its river’s deltas built by sediment carried by the intense episodic rainfalls. For this reason, understanding the leading factor to the last decade’s increase in sediment export is crucial to prevent further degradation of the ecosystems.

A combined approach of sediment sampling and remote sensing was used. Different methodologies were implemented to collect sediments in Lake Kivu close to the outflow of the rivers along the entire Congolese Rivershore of the lake, targeting areas with different landscape attributes. First, volcanic soils and the absence of natural vegetation characterise the northern part. The central part is an area with intensive mining activities, scarce agriculture and frequent landslides. Finally, in the South, we could discriminate two areas, one with high agriculture density but with a natural park at the headwaters, and the area of Bukavu, which combines all previous factors with a high input of pollutants from the city.

The information extracted from the sediment samples, such as nutrients, grain size and pollutants, will be combined with a detailed remote sensing study integrating UAV, Planet and Sentinel imagery to target the possible factors leading to the last decade’s increase in sediment export. This study will enable researchers and policymakers to explore erosion extent, identify possible drivers and hotspots, and work with stakeholders to develop soil conservation strategies.

How to cite: Lizaga, I., Bodé, S., Van Oost, K., Bagalwa, M., Katcho, K., Ciraba, H., Blake, W., Evrard, O., Latorre, B., Navas, A., and Boeckx, P.: In search of the triggers of increasing sediment loads to Lake Kivu, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8614, https://doi.org/10.5194/egusphere-egu23-8614, 2023.

Many of the world’s sedimentary basins feature layered sedimentary rocks with vertical differences in mineralogy, hardness and weathering rates. Landscapes formed in such heterolithic rocks often feature stepped hillslopes, where flatter and steeper sections alternate, resulting from different weathering rates of different lithologies. On occasion, the steeper sections have developed cliff faces where undermining from the underlying, faster weathering lithology causes the slower weathering lithology to collapse and break before developing its own regolith cover. As a result of undermining and collapsing, often unweathered (harder) blocks are found on top of weathered (softer) regolith, and these blocks can move downslope over time. The geomorphic dynamics and rates of change in these landscapes have been insufficiently explored and rarely dated. Specifically, the ability of multiple steps in hillslopes to delay a landscape’s response to baselevel shifts and return to equilibrium remains unknown. Here, we present numerical modelling results as well as 20 cosmogenic exposure dates of cliff faces and blocks on hillslopes that detail key dynamics of a stepped landscape in the Flint Hills, part of the Great Plains sedimentary basin in Kansas in the United States. For modelling, we adapted a recently published 2-dimensional model that combines terms for hillslope diffusion and rock weathering with rules for hard rock break-up and movement through undermining. The model suggests that if hard-to-weather layers are sufficiently numerous, equilibrium at the top of the hillslope is elusive because of the long times needed to undermine hard layers until blocks break off. For exposure dating of our limestone cliffs and blocks, we used the cosmogenic nuclide Chlorine36. Dates suggest that almost all breaking of cliffs and movement of blocks happens during periglacial conditions in the LGM, despite anecdotal evidence of recent small movements of blocks.

How to cite: McCarroll, N. and Temme, A.: Heterolithic Hillslopes in Kansas Seem to Never Reach Equilibrium, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8835, https://doi.org/10.5194/egusphere-egu23-8835, 2023.

Closed basins are commonly found in desert environments. They delineate an excellent configuration with which to study source-to-sink processes. Here we use the Rainbow Canyon-Panamint Valley canyon-fan system, Death Valley, USA as an example for the development of a general numerical model. The upstream region of our study reach is incising into bedrock, with a retreating knickpoint. The downstream region of our study is alluviated, and ends with a closed boundary. In between is a normal fault. The upstream reach is in relative uplift, driving incision (e.g. Argus Range), and the downstream reach is in relative subsidence, driving deposition on an alluvial fan (e.g. Panamint Valley). The closure of the basin at the downstream end provides a simple model of a mountain range on the opposite side of the valley (Panamint Range). We use the model of Zhang et al. (2020) to study a range of conditions. At one end we study the conditions for the formation of a hanging valley, with a vertical waterfall at the fault. At another end we study the conditions for the partial or complete alluviation of the canyon reach. We place emphasis on conditions where the canyon and fan “talk” to each other, versus conditions where the fan becomes a passive recipient of sediment from the canyon. We also show the consequences of opening up the downstream end of the basin, so that sediment is removed at the base of the fan (e.g. Armagosa River). We offer a versatile tool to study source-to-sink morphodynamics in an arid environment.

How to cite: Zhang, L. and Parker, G.: Source-to-Sink Canyon-Fan Interaction in a Closed Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4678, https://doi.org/10.5194/egusphere-egu23-4678, 2023.

Dynamic geodiversity is the study of the ongoing changes in the Earth's geological, geomorphological, climatic, hydrographical/hydrological, and pedological processes, features and landscapes. It encompasses both natural processes, such as erosion and sedimentation, as well as human activities that can impact the Earth's geology or geography, such as mining or land use change. Understanding dynamic geodiversity is important for predicting and managing the impacts of these changes on the environment and further as a consequence on human societies.

There are a few examples of dynamic geodiversity:

• Volcanoes and earthquakes: These geologic events can dramatically alter the landscape and have significant impacts on the environment and human communities.
• Erosion and sedimentation: these processes shape the Earth's surface and create diverse landscapes, such as mountains, valleys, and coastlines.
• Climate change: Changes in the Earth's climate can lead to shifts in the distribution of landscapes, as well as changes in the timing and intensity of geological and geographical processes, such as landslides and coastal erosion.
• Land use change: Human activities, such as urbanization, agriculture, and resource extraction, can have significant impacts on the Earth's surface and the diversity of its features and processes.

Dynamic geodiversity is important for understanding the Earth's environment and its diversity. Examples of erosion and sedimentation processes that change the face of the Earth will be shown during the presentation

How to cite: Zwoliński, Z.: Erosion and sedimentation as drivers of dynamic geodiversity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10401, https://doi.org/10.5194/egusphere-egu23-10401, 2023.

Amongst the adverse consequences of oil palm land-use in the wet tropics are high rates of hillslope and catchment erosion and enhanced downstream channel change, sedimentation and flooding.  These consequences are being exacerbated by some features of current and predicted future climatic change (notably increases in magnitude-frequency-intensity of large rainstorms) and the spread of oil palm to cover greater proportions of landscapes and into steeper terrain.  Although there is growing awareness of these problems within the oil palm industry including the adoption of some conservational measures, such as maintenance of ground covers of low vegetation and piles of palm fronds, retention or restoration of riparian forest strips (or strips of dense low vegetation) and (in steep terrain) of engineered terraces and roadside ditches), the effectiveness of such measures has largely been assumed rather than systematically assessed.  Furthermore, erosion studies have been of catchment sediment yields covering establishment and the early years of oil palm plantation and within-catchment erosion and sediment sources and the mature and old-age phases of the oil plantation cycle have received little attention.  These research gaps form the focus of this paper. It uses results of hydrological components of the long-term (since 2011) multi-catchment Stability of Altered Forest Ecosystems (SAFE) programme investigating impacts of multiple phases of selective logging and conversion to oil palm in the steep headwaters areas of the Kalabakan, Brantian and Segama catchments in eastern Sabah, Malaysian Borneo.  The focus is on a small mature (> 20 year-old) oil palm catchment, but with comparisons with multiple-logged and primary forest catchments. Results are reported for (1) suspended sediment (turbidity) and streamflow dynamics and magnitudes at catchment gauging stations instrumented with depth and turbidity sensors and Campbell data-loggers, (2) soil erosion rates from networks of erosion bridge sites,  (3) channel size and change at networks of repeat-measurement cross-sections, and (4) within-storm observations and measurements of suspended sediment concentrations of road ditches and overland flow.  The findings are used to assess the relative importance of sources of sediment within the oil palm catchment.  The results suggest that erosion from the oil palm slopes and from roadside ditches of the dense road/track network characteristic of oil palm terrain, although significantly higher than from forested slopes, are not the main sources of sediment, which appear to be (1) enlargement of valleyside ephemeral channels by road ditch runoff, as well as (2) erosion of unsurfaced tracks and roads and (3) fluvial erosion.  Possible practical ways to reduce storm sediment and streamflow peaks from oil palm terrain (and thereby reduce downstream sedimentation and flooding problems) are discussed. These include ways of reducing delivery of road runoff to valleyside ephemeral channels and erodible sections of the road/track system by directing road runoff into vegetated soakaways on oil palm slopes.             

How to cite: Walsh, R., Nurhidayu Abu Bakar, S., Nainar, A., Bidin, K., Annammala, K., and Higton, S.: Erosional dynamics, sediment sources and designing strategies to reduce downstream sedimentation and flooding in oil palm terrain in Sabah (Malaysian Borneo). , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16066, https://doi.org/10.5194/egusphere-egu23-16066, 2023.

The earth’s surface and its landforms are a sensitive result of geomorphic processes that tend to balance out. Zambia, together with central and Southern Africa, has been a land mass of the Mesozoic era and likely older. This old land mass has been subject to a complex history of erosion, uplift, faulting (particularly in eastern Zambia) and gentle warping. In Upper Zambezi Basin (UZB), Kabompo District, an interesting landform taking the sharp of an Octopus, a part of the Kalahari sands landform, seems to be a stable feature with a land cover type (vegetation) which it now supports. The Octopus Land Feature (OLF) from satellite imagery appears whitish and devoid of vegetation. Ground-truthing reveals a termitaria landscape with highly scattered shrubs. All around this feature, thick Cryptosepalum forests extending to distances of 20+ km can be observed interspaced with ‘’arms’’ of the OLF.

This landform may be a ‘’pan’’ in the dry season and a dambo in the wet season. Morphometric analysis of the OLF indicates that elongated transverse arms are sources of several streams arising from the interdune depressions of sand ridges that hold rainwater during the rainy season to overflow as sources of rivers that traverse the thick forests. This complex landform-land-cover ecosystem is at risk of degradation and destruction due to increasing human induced fires and commercial logging. Land cover and geomorphic processes play an influential role in maintaining a balanced and functional ecosystem. Conversion of natural landscapes for agriculture and logging often impacts soil integrity, nutrient fluxes, and native species assemblages. Such changes can affect watershed hydrology by altering rates of interception, infiltration, evapotranspiration, and groundwater recharge, resulting in changes to the timing and amounts of surface and river runoff.

This study seeks to understand the implications of land cover changes on the hydrology and materials (sediment & nutrients) through the Kalwilo Community Area (KCA) and the drying of the Mumbenji River. The wanton use of fire in opening up new agricultural areas has been noted to aid in the rapid destruction of forests in the study area. To this aim, a combined approach of soil and sediment sampling together with the use of remote sensing will be employed to establish a link between the rate of deforestation and the sedimentation of the Mumbenji River and its disappeared eflows. It is clear that the drying up of the Mumbenji River, which was once perennial, is a result of the disruption of the landscape system caused by anthropogenic activities.

How to cite: Namayanga, L., Lizaga, I., Sichingabula, H., Boeckx, P., and Banda, K.: Implications of Forest Cover Changes and Fire Management Practices in Kalwilo Area, North-western Province of Zambia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12100, https://doi.org/10.5194/egusphere-egu23-12100, 2023.