Gully Head Research Articles

Evaluation of gully head retreat and fill rates based on high-resolution satellite images in the loess region of China

The acceleration of large gully erosion in the loess environments of China is a matter of concern because of the changing land use and urban expansion. This paper evaluates the gully head retreat and landfill rates in the Huoxianggou watershed in the loess region of China for the period between 1969 and 2017. High-resolution satellite imageries and ground truths allowed us to estimate the linear and volumetric change rates of gully head. The digital elevation model (DEM) derived from unmanned aerial vehicle (UAV) was used to calculate the geometric parameters of the gully bottom, and the linear and volumetric gully parameters were obtained using the 1969, 2004 and 2017 satellite images of the study area. We estimated the average annual linear retreat rate (Rl) for the study area between 1969 and 2003; Rl was found to be 1.41 ± 0.98 m y−1, the average annual volumetric retreat rate (RV) was 63.79 ± 96.62 m3 y−1, the average annual linear fill rate (Fl) was 3.87 ± 4.09 m y−1, and the average annual volumetric fill rate (FV) was 1002.46 ± 1633.87 m3 y−1. Between 2004 and 2017, Rl was 0.82 ± 0.80 m y−1, RV was 1.80 ± 1.37 m3 y−1, Fl was 3.86 ± 4.99 m y−1, and FV was 708.62 ± 1787.21 m3 y−1. We also estimated the retreat and fill rate of gullies within various land use classes. When the land use type near the gully head was road, the volumetric retreat rate of the gully was threefold that of the farmland, and the rate of the gully head landfill was fourfold that of the farmland. Moreover, the volumetric change rate (CV) and linear change rate (Cl) of all gully heads under the influence of a road, including gully retreat and landfill, had a power exponential relationship (CV = 13.29 C 2.14 , R2 = 0.71). The gullies near the roads in the thick loess area were cut at an abnormally rapid rate, which has not received sufficient attention previously. Therefore, the effect of road construction on gully erosion in the loess area of China should be reassessed.

Gully Erosion Induced by Snowmelt in Northeast China: A Case Study

Gully erosion stands out as one of the worst aspects of farmland degradation, which induces the loss of arable soil and tractor operation. Most of the gully erosion studies focused on the influence of precipitation erosion, slope erosion, and the freeze–thaw cycle on soil characteristics. Few studies discussed the effect of snowmelt on gully development. In this paper, the gully development induced by snowmelt was observed in a typical gully in Hailun City, the center of the Mollisols area of northeast China. The results showed that, during the snow melting period of 2017, the soil loss induced by snow melting was 0.22 t at the gully head + 0 m, 14.27 t at the gully head + 77 m, and 7.63 t at the gully head + 239 m, while 98.1% of the sediment was from the gully erosion. The horizontal projected area of the observed gully increased by 56.96 m2, and the gully head advanced 2.3 m during the snow melting period. About 92.2% of the total runoff occurred in the initial snow melting period. The discharge runoff and sediment concentration had a significant correlation with the air temperature above 0 °C, and the same relationship existed between the discharge runoff and sediment concentration in the initial and middle snowmelt stages. The results indicate that the gully development induced by snowmelt should not be ignored in the area.

The Functioning of the Cascade Lithodynamic System of the Kuda River Basin (Upper Angara Region)

The redistribution of sediments in the Kuda river basin as a result of erosion-accumulation processes is investigated from the systems perspective. The current geodynamic position of the basin associated with the transition zone from the Siberian platform to the Baikal rift is emphasized. The contribution of cryogenic, karst and aeolian processes to the mobilization of matter in the system is considered. A quantitative assessment of the amount of transported material in the upper (slope), middle (ravine) and lower (riverbed) lithodynamic zones of the basin was made. Time series of the main hydroclimatic indicators were used to determine the long-term dynamics of the functioning of the basin. Using the satellite images, we identified changes in the economic activities within the basin over the past 30 years. They imply a reduction in croplands and an expansion of grasslands. Calculations show that the annual volume of sediments transported within the basin reaches 3 184 430 tons. Most of them (89%) are involved in the movement by the runoff of storm water, and only 364 405 tons are transported with the runoff of melt water. The role of gully erosion in ablation and sediment transportation is insignificant, because most of the gullies are inactive with a reduction in agriculture; the average growth rate of the heads of gullies does not exceed 0.5 m/year. Channel processes contribute primarily to the redistribution of sediments between adjacent sections of the channel, and their transport to large distances is limited by karst processes and by a significant anthropogenic transformation of the bottoms of the valleys. The annual flow of suspended and transported sediments is a mere 31 000 tons, and the main ablation of material from the system occurs in a dissolved form. In general, the mechanical volume of sediment yield from the system makes up 1%. The rest of material is redistributed in the basin and causes an enhanced accumulation. It is shown that almost half of the sediments is intercepted by large ponds; the rest is accumulated in the bottoms of the valleys in areas with active karst development, on floodplains as well as in talus and proluvial trains. The study determined a general trend in the transformation of the relief as a result of the functioning of the basin implying its planation.

Granite residual soil properties in collapsing gullies of south China: spatial variations and effects on collapsing gully erosion

Collapsing gully erosion, a special erosion phenomenon in the hilly granitic regions, is an important factor responsible for the deterioration of the ecological environment in southern China. The granite residual soil properties tend to vary with soil depth and their spatial variations have an important impact on the formation and development of collapsing gullies. Here, two typical granitic soil profiles in the north boundary of collapsing gully erosion in south China were selected to investigated the spatial variations of soil physicochemical, hydraulic, and mechanical properties along the profile and their influences on collapsing gully erosion. The upper two soil layers (surface soil layer and red soil layer) were significantly different from the lower two soil layers (sandy soil layer and detritus layer) in the investigated properties. The soil texture performed a large variation along the profile, which might be a positive factor for the formation of secondary vertical joints, faults, and weak structural planes. Meanwhile, the lower soil layers had a lower value of PL, LL, organic matter, and iron‑aluminum oxides, demonstrating their poor structure and vulnerability to erosion under rainfall conditions. Additionally, the upper soil layers had a higher water-holding capacity, but a lower decreasing rate in the unsaturated coefficient of permeability, leading to the overburdening of the lower soil layers under rainfall conditions. And the low soil layers had a low shear strength, which could also lead to the sliding of the gully head and sidewall, especially under saturated conditions. Collectively, the special geological structure of the granite residual soil layers plays an important role in the occurrence and development of collapsing gully erosion. The data reported in this paper may facilitate a better understanding of soil mass failure on the gully head and the collapsing gullies.

Changes in soil properties and erodibility of gully heads induced by vegetation restoration on the Loess Plateau, China

Soil erosion on the Loess Plateau of China is effectively controlled due to the implementation of several ecological restoration projects that improve soil properties and reduce soil erodibility. However, few studies have examined the effects of vegetation restoration on soil properties and erodibility of gully head in the gully regions of the Loess Plateau. The objectives of this study were to quantify the effects of vegetation restoration on soil properties and erodibility in this region. Specifically, a control site in a slope cropland and 9 sites in 3 restored land-use types (5 sites in grassland, 3 in woodland and 1 in shrubland) in the Nanxiaohegou watershed of a typical gully region on the Loess Plateau were selected, and soil and root samples were collected to assess soil properties and root characteristics. Soil erodibility factor was calculated by the Erosion Productivity Impact Calculator method. Our results revealed that vegetation restoration increased soil sand content, soil saturated hydraulic conductivity, organic matter content and mean weight diameter of water-stable aggregate but decreased soil silt and clay contents and soil disintegration rate. A significant difference in soil erodibility was observed among different vegetation restoration patterns or land-use types. Compared with cropland, soil erodibility decreased in the restored lands by 3.99% to 21.43%. The restoration patterns of Cleistogenes caespitosa K. and Artemisia sacrorum L. in the grassland showed the lowest soil erodibility and can be considered as the optimal vegetation restoration pattern for improving soil anti-erodibility of the gully heads. Additionally, the negative linear change in soil erodibility for grassland with restoration time was faster than those of woodland and shrubland. Soil erodibility was significantly correlated with soil particle size distribution, soil disintegration rate, soil saturated hydraulic conductivity, water-stable aggregate stability, organic matter content and root characteristics (including root average diameter, root length density, root surface density and root biomass density), but it showed no association with soil bulk density and soil total porosity. These findings indicate that although vegetation destruction is a short-term process, returning the soil erodibility of cropland to the level of grassland, woodland and shrubland is a long-term process (8–50 years).

Assessment of the Sustainability of the Territories Affected by Gully Head Advancements through Aerial Photography and Modeling Estimations: A Case Study on Samal Watershed, Iran

Gully erosion is considered one of the major issues of land sustainability because it can remove considerable volumes of sediment and productive soils. Once started, gullies can continue to move by headcut retreat, or slumping of the side walls. Studies of gully development require constant monitoring activities which are not possible in not-well-explored areas, such as the arduous region of Iran, due to costs and a lack of geoinformation. Thus, the present research attempts to assess gully evolution using only two digital aerial photographs of different periods (1968 and 1994) and field assessment (2009) to estimate the gully head advancement based on frames geometry and rigorous procedure in southwestern Iran. Also, the gully head advancement was estimated and compared among them by different empirical equations. The results indicated that the mean of gully head advancement was 1.4 m year−1 and 1.2 m year−1 during 1968–1994 and 1994–2009, respectively, and the annual average of sediment mobilization was 26.8 m3 ha−1 in 2009. The model assessment indexes indicated that SCS (Soil Conservation Service) II was the best model for gully head advancement estimations in this study area. The main reasons for this can be associated with the Rp factor (previous gully head advancement) and the local environmental conditions. We conclude that the sustainability of the territory has been greatly affected due to this advancement. We also hypothesize that gully head changes could be related to the susceptibility of geological formations, climate, soil properties, and the coincidence of other gullies’ formation with common drainage networks in the study area. Based on the obtained results, land managers can use the results to distinguish the gullies in this region with a higher environmental risk, and to decide an effective implementation of soil conservation measures in order to include them in the land management plans.

Profile distribution of soil moisture in the gully on the northern Loess Plateau, China

Gully is a typical geographical unit and a key component of the slope–gully system on the northern Loess Plateau. Understanding the distribution of soil moisture in gullies aids water resource regulation and ecological restoration. To investigate temporal–spatial variability of soil moisture, we measured values of soil water content (SWC) within 0–500 cm by using a neutron probe on 19 occasions from October 2014 to July 2017 in the gully and bank of a developed gully in Liudaogou catchment of Shenmu County. Results showed that the values of space–averaged soil water storage (SWS) in the gully were significantly (P < 0.01) higher than those in the bank. Soil clay content (SCC) and topography (including site elevation and distance from the gully head) were the most important factors affecting SWS of 0–500 cm in the gully. Topography can indirectly control SWS by redistribution of rainfall and soil properties. SWS and SCC rose with increasing distance from the gully head to the outlet. SWS in the gully exhibited strong temporal stability, and two time–stable sites around the middle section can be used to represent mean SWS within 500 cm depth in the gully. The gully sidewall significantly (P < 0.05) aggravated drought of soils in the bank between 150 and 250 cm from the gully edge. Gullies make the temporal–spatial patterns of soil moisture complex in slope–gully system. These results were expected to improve understanding of soil moisture distribution in the gully region and aid vegetative restoration of the northern Loess Plateau.

Gully head modelling: A Mediterranean badland case study

AbstractPredicting the location of gully heads in various environments is an important step towards predicting gully erosion rates. So far, field data collection and modelling of topographic thresholds for gully head development has mainly focused on gullies that formed in forested areas, rangelands, pastures and cropland. Such information for gullies in badlands however is very scarce. Therefore, this paper aims to extend the database on gully head topographical thresholds through data collection in a badland area and to improve the prediction of gully heads forming at sites with a very low erosion resistance value. For this, we chose a badland site located in central Italy that is characterized by biancana forms and both active and dormant gullies. The definition of the conditions under which present‐day gully heads developed allowed a better modelling of the gully head threshold equation, with modification of a previous model and the exemplification of how to use the updated model. The model shows that the resistance to gully head retreat depends on slope gradient and drainage area at gully heads, land use at the moment of gully development (as numerically expressed using parameters derived from the Runoff Curve Number method), surface rock fragment cover, presence of joints, pipes, and factors/processes affecting detachment rate. This study attempted to better understand environmental conditions that control the development of gully heads in badlands through a combination of field data collection of gully heads, an analysis of land use changes over 10 centuries, focusing on the period 1820–2005, and land use management through repeat photography and a critical examination of historical documents. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley &amp; Sons Ltd.

Natural risk assessment and mitigation of cultural heritage sites in North‐eastern Romania (Valea Oii river basin)

The number of geomorphological processes increases every year around the world. Irrespective of having natural or anthropic causes (gully erosion, landslides), they irreversibly affect the agricultural lands, lakes and ponds (by increasing the sedimentation rate), and cultural heritage. The main objective of this study is to identify and analyse areas susceptible to landslides and the cultural heritage that is in danger in the Valea Oii catchment, North‐eastern Romania. The development of gullies has been observed for 111 years, first in geomorphological annotations and geographical sketches and second in precise monitoring using the total station and GPS. The average gully head advance is 5.46 m/year for the period 1894–2005. In the case of landslides, the results of monitoring have allowed the implementation of a predictive model relying on the available GIS spatial data. The predictive model was validated by overlaying the existing landslides over the susceptibility map. It can be extremely useful in identifying the areas susceptible to landslides threatening cultural and natural heritage, developing anti‐erosion methods, monitoring and creating a sustainable management plan to protect historical monuments. A significant portion of the latter is included in the Romanian List of Historical Monuments. From 47 registered monuments, 27 are located in areas with high and very high susceptibility to landslides. A series of anti‐erosion measures, involving development projects and re‐greening of sites (planting trees), have already been employed in the case of two of the gullies that are affecting archaeological and palaeontological sites.

Variation in soil saturated hydraulic conductivity along the hillslope of collapsing granite gullies

ABSTRACTSaturated hydraulic conductivity (Ks) affects the soil hydrological process and is influenced by many factors that exhibit strong spatial variations. To accurately measure Ks and its scale, spatial variability and relationship with collapsing gullies, we analysed four double-ring infiltrometer diameters in three soil layers during in situ experiments designed to measure Ks in two typical collapsing gullies (three slope sites) in Tongcheng County of China. The results showed that Ks increased with increasing inner ring diameter, but no significant difference existed between inner diameters of 30 and 40 cm. The Ks in red soil layers was higher than that in sandy soil layers, the transition layers had the lowest values. Ks also varied with slope position, gradually decreasing with distance from the gully head. The suggestion is that the spatial variation in Ks is affected not only by the intrinsic soil properties but also by the interaction with the collapsing gully.

Assessment of Practices for Controlling Shallow Valley-Bottom Gullies in the Sub-Humid Ethiopian Highlands

Rehabilitation of large valley bottom gullies in developing countries is hampered by high cost. Stopping head cuts at the time of initiation will prevent large gullies from forming and is affordable. However, research on practices to control shallow gully heads with local materials is limited. The objective of this research was therefore to identify cost-effective shallow gully head stabilization practices. The four-year study was conducted on 14 shallow gullies (&lt;3 m deep) in the central Ethiopian highlands. Six gullies were used as a control. Heads in the remaining eight gullies were regraded to a 1:1 slope. Additional practices implemented were adding either riprap or vegetation or both on the regraded heads and stabilizing the gully bed downstream. Gully heads were enclosed by fencing to prohibit cattle access to the planted vegetation. The median yearly head retreat of the control gullies was 3.6 m a−1 with a maximum of 23 m a−1. Vegetative treatments without riprap prevented gully incision by trapping sediments but did not stop the upslope retreat. The gully heads protected by riprap did not erode. Regrading the slope and adding riprap was most effective in controlling gully head retreat, and with hay grown on the fenced-in areas around the practice, it was profitable for farmers.

Impact of piping on gully development in mid-altitude mountains under a temperate climate: A dendrogeomorphological approach

Gullies are complex geomorphic systems induced and transformed not only by surface erosion processes, but also by subsurface processes such as piping. However, the transient nature of piping makes this process more difficult to observe and study, especially when a pipe roof has totally collapsed. This study aims at assessing piping impact on gully initiation and development using dendrogeomorphological analyses, which are a novel approach in piping study. The survey was carried out in a mountainous area under a temperate climate, using the Bereźnica Wyżna catchment in the Bieszczady Mts. (Eastern Carpathians) as a case study. We estimated the minimum age of pipe collapses and presented the transformation of pipe collapses in order to identify the direction of pipe and gully development. We also verified the contribution of piping to gully development by the reconstruction of gully bottom deepening. The analysis was based on changes in tree and root wood anatomy in diffuse-porous deciduous angiosperm species, i.e. common alder (Alnus glutinosa) and field maple (Acer campestre). The pipe collapses in the piping system studied are at least 19 to 23–27 years old and the pipe roof initially collapsed in the lower sections of the slope (above the gully head) and the pipe develops up the slope by headward erosion. The gully that was analysed in forest had been deepened by piping during several episodes connected with high precipitation events. In contrast, the pipe located in grasslands collapsed 1–2 years after such events indicating that dense vegetation delays pipe collapse. This study shows that dendrogeomorphological analyses based on diffuse-porous deciduous angiosperm species may be a useful tool in piping research. It provides information on pipe and gully development, as well as enabling estimates to be made of the age of pipe collapses.

Gully morphological characteristics in the loess hilly‐gully region based on 3D laser scanning technique

AbstractGully morphology characteristics can be used effectively to describe the status of gully development. The Chabagou watershed, located in the hilly‐gully region of the Loess Plateau in China, was selected to investigate gully morphological characteristics using a 3D laser scanning technique (LIDAR). Thirty‐one representative gullies located at different watershed locations and gully orders were chosen to quantitatively describe gully morphology and establish empirical equations for estimating gully volume based on gully length and gully surface area. Images and point cloud data for the 31 gullies were collected, and digital elevation models (DEMs) with 10‐cm resolution were generated. ArcGIS 10.1 was then used to extract fundamental gully morphological parameters covering gully length (L), gully width (WT) and gully depth (D), and some derivative morphological parameters, including gully head curvature (C), gully width–depth ratio (w/d), gully bottom‐to‐top width ratio (WB/WT), gully surface area (Ag) and gully volume (Vg). The results indicated that gullies in the upper watershed and the second order were more developed based on their high values of gully head curvature. The potential for gully development increased from the second order to the fourth order. Within the same gully orders, gullies in the lower watershed were more active with more development potential. A method for differentiating between gully head and gully sidewalls based on the gully head curvature value was proposed with a mean relative error of 8.77%. U‐shaped cross‐sections were widely distributed in the upper watershed and upper positions of a gully, while V‐shaped cross‐sections were widely distributed in the lower watershed and lower positions of a gully. V–L and V–Ag empirical equations with acceptable accuracy were established and can be used to estimate gully erosion in the Loess hilly‐gully region. Copyright © 2017 John Wiley &amp; Sons, Ltd.

Mean Rate of Gully Head Advancement in Edo State, Nigeria

The issue of gully erosion is of major concern in Nigeria. The study was carried out in Edo state, Southern Nigeria. Edo State was chosen as the study area due to the fact that the magnitude of gully erosion has resulted in the loss of lives and properties, destruction of arable lands and wastage of large areas of usable land. In this study, an effort was made to identify the major gully sites in the area and determined the mean rate of gully head advancement. The result revealed that gullies in Edo North had mean rate of head advancement of 80.30 meters per a year, Edo South 52.03 meters per a year and Edo Central is 17.80 meters per year.

Influences of soil erosion susceptibility toward overloading vulnerability of the gully head bundhs in Mayurakshi River basin of eastern Chottanagpur Plateau

Soil erosion in the upper catchment of lateritic belt of the Mayurakshi River is one of the major problems. Excessive soil erosion leads the gully head bundhs (reservoir) hyper sedimented. These bundhs were constructed under Massanjore Dam projects for arresting soil erosion and reducing sedimentation rate in the reservoir of the Massanjore Dam. This paper intended to investigate the present state of gully head reservoirs in connection with sedimentation and find out whether these vulnerable gully head bundhs are located at the extremely soil erosion susceptible zone. Soil erosion and gully head over loading vulnerability models generated in this aim, and it is found that highly vulnerable gully head bunds are located at the excessive soil erosion zone and therefore these two models are spatially correlated. It is revealed that in the extremely susceptible soil erosion zone, 105 nos. or 52.5% to total extremely overloading vulnerable gully head bundhs are located and frequency density of them in the same area is 0.1204 nos./sq km. From this spatial adjacency, it can be stated that extreme soil erosion susceptibility and soil loss (19.62 Mg/ha/year) are principally responsible for making the reservoirs vulnerable. These reservoirs play vital role for arresting soil erosion, and as these are not evenly distributed even in the extremely soil erosion susceptible zone, more number of such reservoirs can be installed there.

Gully Head Retreat in the Sub‐Humid Ethiopian Highlands: The Ene‐Chilala Catchment

AbstractIn the northern highlands of Ethiopia, gully erosion is severe. Despite many efforts to implement gully prevention measures, controlling gully erosion remains a challenge. The objective is to better understand the regional gully erosion processes and to prevent gully head retreat. The study was conducted in the Ene‐Chilala catchment in the sub‐humid headwaters of the Birr River located southwest of Bahir Dar, Ethiopia. Twelve gully heads were monitored during the 2014 and 2015 rainy monsoon phase. We measured gully head morphology and retreat length, soil shear strength, ground water table levels, and catchment physical characteristics. Two active gully head cuts were treated in 2014 and an additional three head cuts in 2015 by regrading their slope to 45° and covering them with stone riprap. These treatments halted the gully head advance. The untreated gullies were actively eroding due to groundwater at shallow depths. The largest head retreat was 22.5 m, of which about half occurred in August of the first year when the surrounding soil was fully saturated. Lowering both the water table and protecting the gully heads can play a key role in reducing gully expansion and soil loss due to gully erosion in the Ethiopian highlands. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Long-term monitoring of gully erosion in Udmurt Republic, Russia

Abstract. This article presents results from the long term-monitoring of gully headcut retreat rates (GHRR) between 1959 and 2015 in different parts of the Udmurt Republic and is based on the use of historical aerial photographs and field observations (measuring the distance from the gully head to a fixed reference point) (Vanmaercke et al., 2016). It was determined that GHRR decreased from 2.4 to 0.3 m yr−1 during the 1959–1997 observation period and the 1998–2015 period, respectively. Measurements of GHRR were made once per year for most of the monitoring sites, and twice per year (after snow-melt in May, and after the rainy season, October–November) for gullies located in the eastern part of the study area that contain high proportions of arable land. 80 % of GHRR occurred during the snowmelt period (1978–1997), and decreased to 53 % since 1997. Spatial patterns of GHRR resulting from changing hydro-climatic factors for different regions of the Udmurt Republic, as a whole, were determined based on the analysis of long-term observations at 6 meteorological stations and 4 gauging stations. The main reason for decreasing GHRR appears to be due to reductions in winter frozen soil depth. The influence of stormwater runoff more clearly occurred within the east and north parts of the Vyatka-Kama interfluve, whereas higher correlations between GHRR and frozen soil depth were found for the western parts of the Republic. The most significant increases in GHRR appear to have occurred during the warm part of the year (June–July), after &gt; 40 mm rainstorms.

Effect of Gully Headcut Treatment on Sediment Load and Gully Expansion in the Sub Humid Ethiopian Highlands

The Ethiopian government has been implementing a land restoration program that aimed to restore degraded ecosystems and double agricultural productivity throughout the country since 2010. However, the success of the restoration program has been limited due to the lack of integrating gully erosion control measures. Consequently, many reservoirs in Ethiopia and downstream riparian countries have lost their storage capacity due to sedimentation, and studies demonstrated that gully erosion is one of the degradation hotspots within watersheds and contribute considerable proportion of the total sediment loads from a particular watershed. This study was conducted in one of large gullies in the Debre-Mawi watershed, northwestern Ethiopia to quantify the effect of gully head treatment in reducing the amount of sediment load generated from uplands and from the gully itself. We measured discharge, and sediment load and concentration in 2013 and 2014 at the upstream (inlet) and downstream ends (outlet) of the studied gully. Before the 2014 rainy phase, a gully headcut was stabilized with gabions at the bed and the gully bank was regarded to 45o. The gully head retreated 12 m in 2013 but gully head retreat was stopped following the implementation of the treatment in 2014. The total sediment load and sediment concentration at the outlet was reduced by 42% and 30% respectively, in 2014 (i.e., after treatment) when compared to 2013 (i.e., before treatment). The result of this study support that controlling the upward retreat of gully head is effective in reducing sediment load and concentration as well as upward movement and expansion of gullies. However, maintenance of gully head control measures is the key to sustain the benefits.

INFLUENCE OF CLIMATE CHANGE ON THE RATES OF GULLY GROWTH IN THE VYATKA-KAMA WATERSHED

Mean annual rates of gully head retreat were assessed based on the results of monitoring (period 1978–2014) of more than 120 gully heads located within 28 sites over the Vyatka-Kama interfluve area. The main attention was given to evaluation of the ratio of snowmelt- and rainstorm-induced erosion in the total figure of gully head retreat in the entire period of observation. The other focus was the evaluation of the relative contribution of different soil and climatic factors to the gully growth rates in the period 1998–2014. It was found that the mean annual gully head retreat rates had decreased from 1.3 m/year in 1978–1997 to 0.3 m/year in 1998–2014. Observations at a number of locations nearby the Izhevsk city allowed to estimate that the total amount of gully head retreat associated with the snowmelt season had decreased from 80% in 1978–1998 to 53% in the following period. This decline was driven by the considerable decrease of snowmelt water runoff, which in turn was caused by warming of winters and in particular by the decrease of recurrence of winters when the average depth of frozen soil exceeded 50 cm. In the Udmurt Republic, the number of rainstorms capable of production of surface water runoff had increased in 1983–2014 by 20% compared to the period 1962–1982. Therefore, one can suggest that before 1982, the contribution of rainstorm runoff to the mean annual gully head retreat rate was even less than 20%. Rainstorm frequency was found to have not changed significantly during 1983–2014. The most important contribution to gully growth during the warm part of the year comes from rainstorms with the amount of precipitation above 40 mm per one event.

The use of SfM-photogrammetry to quantify and understand gully degradation at the temporal scale of rainfall events: an example from the Ethiopian drylands

With the recent technological advances offered by SfM-photogrammetry, we now have the possibility to study gully erosion at very high spatial and temporal scales from multi-temporal DEMs, and thus to enhance our understanding of both gully erosion processes and controls. Here, we examine gully degradation and aggradation at a gully headcut and at four re-incisions along a gully reach in Northern Ethiopia. Environmental controls recorded are topography rainfall, runoff, land use and cover, land management, and soil characteristics. The overall vulnerability of the catchment to erosion is low as calculated from the RUSLE (average 11.83 t ha−1 y−1). This reflects the successful land management of the past years. The runoff coefficient was on average 7.3% (maximum 18.2%). Runoff events caused most geomorphic change in the gully, but slumping of the gully bank also occurred on dry days. Most geomorphic change was caused by one major rainfall event of 54.8 mm d−1, and smaller runoff events caused both degradation and aggradation, often asynchronous between studied sites. Although most research focuses on gully heads alone, re-incisions at lower locations can still cause important gully degradation, which ultimately will reach the gully head and cause instability.