Exploring the effects of seismicity on landslides and catchment sediment yield: An Italian case study

Recent studies showed that contemporary average catchment sediment yields (SY, [t km− 2 y− 1]) at regional and continental scales are often strongly correlated to spatial patterns of seismic activity. Nonetheless, we currently have little insights into the mechanisms that explain these correlations. We investigated how spatial patterns of SY in Italy are linked to patterns of seismic activity. For a dataset of 103 Italian catchments with average SY measured over a period of years to decades, we extracted tectonic and none-tectonic variables that potentially explain observed differences in SY. These include proxies for vertical uplift rates and cumulative seismic moments (CSM) associated with historic earthquakes of different ranges of magnitude. Results showed that also across Italy, SY is significantly correlated to seismicity. However, SY showed much stronger correlations with proxies of seismicity relating to small but frequent earthquakes (2 ≤ Mw < 4) than with proxies relating to tectonic uplift or large, potentially landslide-triggering earthquakes (Mw ≥ 4). Analyses of a dataset of about 500,000 landslides across Italy showed very comparable trends: spatial patterns of landslides within similar lithological units generally show a significant positive correlation with CSM of weak but frequent seismicity and generally not with CSM of large earthquakes. These results suggest that, on a decadal time scale and at a regional/continental spatial scale, frequent but relatively weak seismicity may exert a more important geomorphic impact than large earthquake events or tectonic uplift. © 2016 Elsevier B.V

Elucidating suspended sediment dynamics in a glacierized catchment after an exceptional erosion event: The Djankuat catchment, Caucasus Mountains, Russia

Suspended sediment yields from glacierized catchments are often among the highest in the world, and their sediment dynamics can be highly variable. This study was undertaken in the 9.1 km2 glacierized catchment of the Djankuat River located in the Russian part of the Northern Caucasus. The outlet of the study catchment is a hydrological gauging station located at an altitude of 2635 m a.m.s.l. (‘N43◦12′31.71′′, E42◦44′05.93′′). The catchment includes a temperate valley glacier (area = 2.42 km2) and three smaller hanging glaciers, several moraine deposits, rock walls, and a large and expanding proglacial area. The main goal of our study was to assess the impact of an exceptional erosion event on 1st July 2015 (with an annual exceedance probability of less than 0.1%) on suspended sediment yields and the relative contributions of various sediment sources The work combined direct suspended sediment discharge measurements at the gauging station during five ablation seasons (2015–2019) with geomorphic mapping techniques based on detailed field observations and sediment source fingerprinting. Results show that mean annual suspended sediment yields reached 1118 t km− 2 year− 1 which is one of the highest measured estimates for any of the glacierized mountain rivers globally. About half of the annual suspended sediment flux was exported during a limited number (1–12% of the annual events) of extreme hydrological events. The sediments mobilized by bank and riverbed erosion within the new lower reach of a tributary channel which appeared after the breakthrough of a lateral moraine became the primary sediment source. It contributed over 50% of the suspended sediment on days with extreme rainfall. Contributions to the suspended sediment load from the glacier source were event-dependent and were only dominant (c. 60–70%) in the upper reaches of the proglacial area (first 800 m). The proglacial part of the study catchment with buried ice was the main sediment source (79%) during non-rain days

Mapping and spatial-temporal assessment of gully density in the Middle Volga region, Russia

© 2018 John Wiley & Sons, Ltd. A large-scale mapping of gully density was carried out for the Middle Volga region of the Russian Plain (188 000 km2) based on the interpretation of aerial photographs (scale 1:17 000; surveys undertaken during 1956–1970). In addition, spatial-temporal dynamic of gully density were assessed for some parts of the study area (the Udmurt Republic and the Mesha and Ulema River basins of Tatarstan), based on the interpretation of aerial photographs (survey 1986–1991) and high resolution satellite images (2012–2015). Information on factors potentially controlling gully formation and development were collected and a geographic information system (GIS) analysis was conducted. Results show the strong development of gullies in the study area over the 1956–1970 period with an average gully density of 0.21 km km−2. For the Udmurt region, we found that gully densities varied little in the period 1956–1986, during which the total active gully length reduced with only 2%. This period was characterized by low variable climatic conditions and a stable fraction of arable land with a relatively continuous crop rotation system. However, gully dynamics seems to have changed more strongly during recent decades. We found a strong (order of magnitude) reduction in active gully density for the period 2010–2015 as compared to 1986–1991. The main reason for this is likely the increasing winter air temperatures. This leads to a significant reduction in surface runoff during spring as a result of snowmelt. Nonetheless, in some regions (i.e. the Udmurt Republic in the taiga zone), the abandonment of arable land after 1991 likely plays a significant role. Likewise, a decline in the frequency of extreme rainfall events (> 50 mm) may have played a role. All of these factors contribute to a reduction of surface runoff to the gullies and their subsequent stabilization. © 2018 John Wiley & Sons, Ltd

EUSEDcollab: a network of data from European catchments to monitor net soil erosion by water

As a network of researchers we release an open-access database (EUSEDcollab) of water discharge and suspended sediment yield time series records collected in small to medium sized catchments in Europe. EUSEDcollab is compiled to overcome the scarcity of open-access data at relevant spatial scales for studies on runoff, soil loss by water erosion and sediment delivery. Multi-source measurement data from numerous researchers and institutions were harmonised into a common time series and metadata structure. Data reuse is facilitated through accompanying metadata descriptors providing background technical information for each monitoring station setup. Across ten European countries, EUSEDcollab covers over 1600 catchment years of data from 245 catchments at event (11 catchments), daily (22 catchments) and monthly (212 catchments) temporal resolution, and is unique in its focus on small to medium catchment drainage areas (median = 43 km(2), min = 0.04 km(2), max = 817 km(2)) with applicability for soil erosion research. We release this database with the aim of uniting people, knowledge and data through the European Union Soil Observatory (EUSO)

How fast do gully headcuts retreat?

© 2016 Elsevier B.V. Gully erosion has important on and off site effects. Therefore, several studies have been conducted over the past decades to quantify gully headcut retreat (GHR) in different environments. Although these led to important site-specific and regional insights, the overall importance of this erosion process or the factors that control it at a global scale remain poorly understood. This study aims to bridge this gap by reviewing research on GHR and conducting a meta-analysis of measured GHR rates worldwide. Through an extensive literature review, GHR rates for 933 individual and actively retreating gullies have been compiled from more than 70 study areas worldwide (comprising a total measuring period of >19 600 years). Each GHR rate was measured through repeated field surveys and/or analyses of aerial photographs over a period of at least one year (maximum: 97 years, median: 17 years). The data show a very large variability, both in terms of gully dimensions (cross-sectional areas ranging between 0.11 and 816 m2 with a median of 4 m2) and volumetric GHR rates (ranging between 0.002 and 47 430 m3 year- 1 with a median of 2.2 m3 year- 1). Linear GHR rates vary between 0.01 and 135 m year- 1 (median: 0.89 m year- 1), while areal GHR rates vary between 0.01 and 3628 m2 year- 1 (median: 3.12 m2 year- 1). An empirical relationship allows estimating volumetric retreat rates from areal retreat rates with acceptable uncertainties. By means of statistical analyses for a subset of 724 gullies with a known contributing area, we explored the factors most relevant in explaining the observed 7 orders of magnitudes of variation in volumetric GHR rates. Results show that measured GHR rates are significantly correlated to the runoff contributing area of the gully (r2 = 0.15) and the rainy day normal (RDN; i.e. the long-term average annual rainfall depth divided by the average number of rainy days; r2 = 0.47). Other factors (e.g. land use or soil type) showed no significant correlation with the observed GHR rates. This may be attributed to the uncertainties associated with accurately quantifying these factors. In addition, available time series data demonstrate that GHR rates are subject to very large year-to-year variations. As a result, average GHR rates measured over short (100%) uncertainties. We integrated our findings into a weighted regression model that simulates the volumetric retreat rate of a gully headcut as a function of upstream drainage area and RDN. When weighing each GHR observation proportional to its measuring period, this model explains 68% of the observed variance in GHR rates at a global scale. For 76% of the monitored gullies, the simulated GHR values deviate less than one order of magnitude from their corresponding observed value. Our model clearly indicates that GHR rates are very sensitive to rainfall intensity. Since these intensities are expected to increase in most areas as a result of climate change, our results suggest that gully erosion worldwide will become more intense and widespread in the following decades. Finally, we discuss research topics that will help to address these challenges

How long should we measure? An exploration of factors controlling the inter-annual variation of catchment sediment yield

Purpose: Although it is well-known that catchment suspended sediment yields (SY; tons per square kilometre per year) can vary significantly from year to year, little information exists on the magnitude and factors controlling this variability. This is crucial to assess the reliability of average SY values for a given measuring period (MP) and is of great geomorphic significance. This paper aims to bridge this research gap. Materials and methods: A worldwide database was compiled with time series of measured SY values. Data from 726 rivers (mostly located in Europe, the Middle East and the USA) were collected, covering 15,025 annual SY observations. The MPs ranged between 7 and 58 years, while catchment areas (A) ranged between 0.07 and 1.84 × 106 km2. For 558 catchments, the annual runoff depths corresponding to the SY observations were also available. Based on this database, inter-annual variability was assessed for each catchment, and relationships with factors potentially explaining this variability were explored. Results and discussion: Coefficients of variation of SY varied between 6% and 313% (median 75%). Annual SY data were generally not normally distributed but positively skewed. Inter-annual variability generally increased with increasing average SY. No significant relationship was found between the inter-annual variability of SY and A, while weak but significant relationships were noted with the variability in annual runoff and rainfall depths. Detailed analyses of a sub-dataset corresponding to 63 catchments in Romania revealed no clear relationships between inter-annual variability of SY and land-use or topographic characteristics. Nevertheless, indications were found that variability was larger for catchments with erosion-prone land-use conditions. Using a Monte Carlo simulation approach, the effect of inter-annual variability on the reliability of average SY data was assessed. Results indicate that uncertainties are very large when the MP is short, with median relative errors ranging between -60% and 83% after 5 years of monitoring. Furthermore, average SY values based on short MPs have a large probability to underestimate, rather than to overestimate, the long-term mean. For instance, the SY value of a median catchment after a 1-year MP has a 50% probability of underestimating the long-term mean by about 22%. Uncertainties quickly decrease after the first few years of measurement but can remain considerable, even after 50 years of monitoring. Conclusions: It is important to consider uncertainties associated with average SY values due to inter-annual variability, for example when attempting to predict long-term average SY values using a steady-state model, as such uncertainties put fundamental limits to the predictive capabilities of such models. © 2012 Springer-Verlag

Erosión y desertificación.-Assessment of the effectiveness of soil and water conservation measures in reducing runoff and soil loss: establishment of a European database

ABSTRACT Soil erosion by water is recognised as a major soil degradation process that requires a global approach. Large regions all over the world are in need of integrated conservation strategies that sustainably prevent and remediate soil erosion. Therefore, quantitative and globally interpretable data are needed in support of models and decision making. The effects of various soil and water conservation techniques (SWCT) on runoff and soil loss in Europe have been extensively studied over the last 60 years. Runoff plots are the most widely used measurement technique to study the effects of SWCT on runoff and soil loss by water erosion. Hence, many data are available. However, the insights gained hereby remain mostly local and often qualitative whereas the full potential of the available data is not exploited yet. This is mainly due to the fragmentation of knowledge and extrapolation difficulties inherently linked with this type of data. This study addresses the issue of the availability of quantitative runoff and soil loss data from plot measurements in Europe and the quantitative assessment of the effectiveness of various SWCT in reducing runoff and soil loss. In the framework of the EU-DESIRE project, a database is currently compiled. The database currently contains 3175 plot-year data on runoff and soil loss measurements from 108 study sites in Europe and the Mediterranean. The SWCT documented herein include crop rotations, conservation tillage, cover cropping, mulching, vegetated buffer strips and terraces. From this dataset, an evaluation can be made of the effectiveness of various SWCT in reducing runoff and soil loss by water for a range of environmental conditions in Europe. A first example, regarding the effectiveness of SWCT in olive orchards, is discussed in this paper

Suspended sediment budget and intra-event sediment dynamics of a small glaciated mountainous catchment in the Northern Caucasus

© 2020, Springer-Verlag GmbH Germany, part of Springer Nature. Purpose: The sediment dynamics of (peri-)glacial catchments can be highly variable and complex. Understanding these dynamics and their underlying causes is not only of interest from a scientific perspective but also required to address the practical problems with which they are often associated. In order to better understand the sediment dynamics of glaciated mountainous catchments, suspended sediment fluxes in the 9.1 km2 Djankuat catchment (North Caucasus, Russia) were monitored intensively during the 2017 ablation season. Materials and methods: The intra-event suspended sediment dynamics were studied using a newly proposed simple hysteresis index (SHI), quantifying to what extent evolutions in sediment concentration are characterized by a clockwise or anticlockwise hysteresis loop. Results and discussion: The resulting catchment suspended sediment yield was 1033 t km−2 year−1, with the glacier itself contributing 72% of the suspended sediment load. However, during rainfall events, also hillslope erosion in the proglacial area became a very significant sediment source. Clockwise hysteresis loops occurred in 61.8% of the events, while anticlockwise in 11.8%. On the other hand, only 47.8% of the total suspended sediment flux was transported during clockwise events. Our observations clearly indicate that events showing a stronger clockwise pattern (i.e., a higher SHI) are associated with a larger sediment input from the proglacial area. Conclusions: Overall, our results provide data and insights on sediment dynamics in an understudied environment. They illustrate that the type and characteristics of sediment concentration hysteresis loops are to some extent linked to the dominant sediment sources during the event. As such, the proposed methodology and SHI may also help with a better understanding of sediment dynamics in other environments

Mapping and spatial-temporal assessment of gully density in the Middle Volga region, Russia

© 2018 John Wiley & Sons, Ltd. A large-scale mapping of gully density was carried out for the Middle Volga region of the Russian Plain (188 000 km2) based on the interpretation of aerial photographs (scale 1:17 000; surveys undertaken during 1956–1970). In addition, spatial-temporal dynamic of gully density were assessed for some parts of the study area (the Udmurt Republic and the Mesha and Ulema River basins of Tatarstan), based on the interpretation of aerial photographs (survey 1986–1991) and high resolution satellite images (2012–2015). Information on factors potentially controlling gully formation and development were collected and a geographic information system (GIS) analysis was conducted. Results show the strong development of gullies in the study area over the 1956–1970 period with an average gully density of 0.21 km km−2. For the Udmurt region, we found that gully densities varied little in the period 1956–1986, during which the total active gully length reduced with only 2%. This period was characterized by low variable climatic conditions and a stable fraction of arable land with a relatively continuous crop rotation system. However, gully dynamics seems to have changed more strongly during recent decades. We found a strong (order of magnitude) reduction in active gully density for the period 2010–2015 as compared to 1986–1991. The main reason for this is likely the increasing winter air temperatures. This leads to a significant reduction in surface runoff during spring as a result of snowmelt. Nonetheless, in some regions (i.e. the Udmurt Republic in the taiga zone), the abandonment of arable land after 1991 likely plays a significant role. Likewise, a decline in the frequency of extreme rainfall events (> 50 mm) may have played a role. All of these factors contribute to a reduction of surface runoff to the gullies and their subsequent stabilization. © 2018 John Wiley & Sons, Ltd