Formation Of Ephemeral Gullies Research Articles

Factors Influencing Ephemeral Gullies at the Regional Scale: Formation and Density

Ephemeral gully (EG) erosion is an important type of water erosion. Understanding the spatial distribution of EGs and other influencing factors at a regional scale is crucial for developing effective soil and water management strategies. Unfortunately, this area has not been sufficiently studied. The present study visually interpreted the EGs based on Google Earth images in 137 small watersheds uniformly distributed in the Loess Plateau, compared them with measured results, and analyzed the factors influencing EG formation and density using GeoDetector. The results showed that visually interpreting EGs from Google Earth images was suitable for EG regional studies. Out of the 137 small watersheds, 33.6% had EG occurrence with an average density of 3.41 km/km2. Rainfall (R) and slope gradient (S) were the primary factors influencing the formation of EGs, while the area proportion of sloping farmland (APSF) and soil erodibility (K) were the main factors affecting EG density. The interaction of dual factors had a greater influence compared to single factors, with the interaction between S and Normalized Difference Vegetation Index (NDVI) having the greatest impact on EG formation and the interaction between K and NDVI on EG density. Although natural forces significantly influence whether EGs can form in a specific area, human activities greatly affect the density of the gullies that develop. This underscores the importance of proper land management in controlling gully erosion. These findings could provide theoretical support for EG prediction models and a scientific basis for soil and water loss control strategies at the regional scale.

Investigating the stability of contour ridge system using rare earth element tracers under natural rainfall in the rocky mountain areas of Northern China

Erratic and intensively erosive natural rainfall is becoming more frequent with the intensification of global climate warming, increasing uncertainty and unpredictable risks of the stability of contour ridge system. However, little attention has been paid to the in situ quantitative evaluation of contour ridge stability under natural rainfall. When water ponds in furrows, contour ridges tend to breach, inducing contour failure followed by ephemeral gully erosion, which greatly affects the stability of contour ridge system. To track sediment sources during ridge slope erosion, contour failure, and ephemeral gully erosion stages, ten rare earth element (REE) tracers were applied in three soil layers (total 0.3 m in depth) at four slope positions in-situ runoff plots under five rainfall levels. Runoff plots were conducted with contour ridgess for sweet potatoes (SP) and peanuts (PT). The stability of contour ridges was gradually weakened when erosion form shifted from ridge slope erosion to contour failure and then to ephemeral gully erosion. Ridge slope erosion controlled contour ridge stability, with contribution of 76.28–80.49 % to the total sediment yield. Sediment yield occupied 40.99 % of the total after contour failure appearing and 55.80 % after ephemeral gully formation. The lower-middle slope was the most fragile area for contour ridge system. Rainstorm (with precipitation 50–100 mm in 24 h) played a destructive role in weakening contour ridge stability, which generated the largest runoff (36.81–39.25 % to the total) and sediment yield (46.75–57.84 % to the total). Rainstorm made the greatest contribution to the occurrence of ridge slope erosion (51.64–59.99 %), contour failure (38.07–40.91 %), and ephemeral gully erosion (24.32–30.53 %). When using REE oxides to determine contour ridge stability, the tagging depth above 0.2 m and the uniform binding of oxides with < 0.05 mm particles should be considered. Thus, some modifications to lower the likelihood of ridge failures under rainstorm conditions may be effective to enhance the stability of contour ridge system.

Effects of sediment yield fluctuations on the niche-like ephemeral gully formation in granite red soil

The granite red soil area in southern China has been afflicted by severe and large-scale gully erosion, locally known as “Benggang” erosion. It is generally believed that Benggang develops from the earlier gully; however, this remains disputed. Therefore, we investigated the rills and ephemeral gullies in the Yanglong watershed of the Hubei Province to explore the initial developmental process of Benggang. The results indicate that a unique gully with a niche-like morphology was found, which was named niche-like ephemeral gully (NEG). The NEG morphology was as follows: a distinct rill upstream, steep bank, a narrow upper bank, and a wide and deep gully bed. The NEG was formed on the exposed sandy soil layer and a local slope which was steeper than 30°. The field runoff scouring experiment simulating NEG formation was conducted on two slopes (20° and 40°) and with two runoff flows (3 L/min and 6 L/min) on three naturally exposed soil layers due to early surface soil erosion (B1 and B2 red clay, and sandy soil layers). The experimental results revealed that the total sediment yield of the sandy soil layer was at most 24.39 times higher than that of the B1 layer under the same treatment. Furthermore, compared to upper red clay layers, the deeper sandy soil layer formed more bank collapse due to faster soil moisture variations and higher soil pore water pressure, thus prompting more drastic sediment yield fluctuations and NEG formation. Therefore, the NEG was primarily formed in the sandy soil layer and was influenced by gravitational erosion represented by bank collapse. The amount of bank collapse and sediment yield differed in the three exposed soil layers, which could be essential for the development of rill into the NEG. Therefore, the NEG is a critical stage where the rill evolves into Benggang from the predominant hydraulic erosion into gravity erosion. These findings provide a new possibility for the origin of Benggang.

Ephemeral gullies caused by snowmelt: A ten-year study in northeastern China

Ephemeral gully erosion of cultivated land may be serious in early spring because of snowmelt runoff and lack of vegetation cover during this period. The snow in winter is redistributed by winds and accumulates in low-lying gullies, furrows, forest shelterbelts and forest lands, which become the main source of snowmelt runoff in spring. This study selected three different hillslopes according to snow redistribution in the black soil region of northeastern China and investigated the ephemeral gully erosion caused by snowmelt runoff from 2009 through 2018. The results showed that drainage area was the main controlling factor of ephemeral gully development. Due to the influence of snow redistribution, volumetric soil loss of ephemeral gully erosion in cultivated hillslopes affected by forestland and forest shelterbelt were more than 2 times greater than that of cultivated hillslopes without other sources of snowmelt runoff. A snow redistribution factor, SR, calculated through surveyed snow depth, accounted for the influence of snow redistribution on ephemeral gully erosion. Ridge tillage increased the threshold value of runoff needed for initial formation of ephemeral gullies, and decreased the number of gullies formed, but it also accelerated the development of single ephemeral gullies once they formed because furrows accumulated more runoff feeding to the drainage areas. A tillage practice factor, T, was used to reflect the influence of ridge tillage on ephemeral gully erosion. A statistical model for estimating ephemeral gully volume was developed that included as independent variables snowfall (SN), snow redistribution factor (SR), drainage area (A) and tillage practice factor (T). Using these parameters, along with bulk density of soil (BD), soil loss (Mg) by ephemeral gullies was estimated to be 0.102*SN1.104*SR*A0.90 *T3.0 *BD (R2 = 0.76).

Effects of Sediment Yield Fluctuations on the Niche-Like Ephemeral Gully Formation in Granite Red Soil

Effects of Sediment Yield Fluctuations on the Niche-Like Ephemeral Gully Formation in Granite Red Soil

An approach to identifying and evaluating the potential formation of ephemeral gullies in the conditions of the Czech Republic

Soil erosion, including ephemeral gully erosion, is a serious degradation process in the Czech Republic. It currently threatens more than half of the agricultural acreage through negative changes in the whole complex of soil properties. The unfavourable consequences of surface runoff are seen in the erosion processes degrading agricultural soils. The South Moravia Region was selected as the case study area – mainly for its natural conditions and high soil degradation risk . A set of data, collected from 2012 to 2017 in a maize-growing area, especially on deep loess soils in the South Moravia Region, was used to analyse the morphological characteristics of the ephemeral gullies (EGs). The relationship was confirmed between the ephemeral gully (EG) length and the size of its contributing drainage area in accordance with studies conducted in other countries. It is also important that the closest relationship was confirmed between the length of the gully and its calculated volume. Dependence was sought on the data of 51 cases of the detailed, measured and evaluated EGs. These results will become the basis for finding a predictive relationship and the quantification of EG erosion. Locating EGs and predicting their length is crucial for estimating the sediment load and planning conservation strategies. The aim of this paper is to contribute to the understanding of this issue, i.e., define and verify the basic crucial causal factors and propose guidelines for locating the potential EG occurrence and predicting the sediment load. A research effort to better understand the EG mechanism and causal factors over a wide range of watershed conditions is fundamental to the establishment of basic rules for the adoption of optimal conservation strategies.

Assessment of soil factors controlling ephemeral gully erosion on agricultural fields

AbstractThe soil factor is crucial in controlling and properly modeling the initiation and development of ephemeral gullies (EGs). Usually, EG initiation has been related to various soil properties (i.e. sealing, critical shear stress, moisture, texture, etc.); meanwhile, the total growth of each EG (erosion rate) has been linked with proper soil erodibility. But, despite the studies to determine the influence of soil erodibility on (ephemeral) gully erosion, a universal approach is still lacking. This is due to the complex relationship and interactions between soil properties and the erosive process. A feasible soil characterization of EG erosion prediction on a large scale should be based on simple, quick and inexpensive tests to perform. The objective of this study was to identify and assess the soil properties – easily and quickly to determine – which best reflect soil erodibility on EG erosion. Forty‐nine different physical–chemical soil properties that may participate in establishing soil erodibility were determined on agricultural soils affected by the formation of EGs in Spain and Italy. Experiments were conducted in the laboratory and in the field (in the vicinity of the erosion paths). Because of its importance in controlling EG erosion, five variables related to antecedent moisture prior to the event that generated the gullies and two properties related to landscape topography were obtained for each situation. The most relevant variables were detected using multivariate analysis. The results defined 13 key variables: water content before the initiation of EGs, organic matter content, cation exchange capacity, relative sealing index, two granulometric and organic matter indices, seal permeability, aggregates stability (three index), crust penetration resistance, shear strength and an erodibility index obtained from the Jet Test erosion apparatus. The latter is proposed as a useful technique to evaluate and predict soil loss caused by EG erosion. Copyright © 2018 John Wiley &amp; Sons, Ltd.

Evaluating ephemeral gully erosion impact on Zea mays L. yield and economics using AnnAGNPS

Ephemeral gully erosion causes serious water quality and economic problems in the Midwest United States. A critical barrier to soil conservation practice adoption is often the implementation cost, although it is recognized that erosion reduces farm income. Yet few, if any, understand the relationship between cost of conservation practice implementation and potential economic benefit gained from erosion control practices, especially as related to ephemeral gully erosion. The objectives of this research are to: (1) evaluate the soil loss and corresponding topsoil depth reduction due to annually ephemeral gully filling; and (2) estimate the economic loss associated with the crop production reduction attributed to topsoil thinning. Surface runoff and watershed sediment yield were flume measured at the approximately 1-ha drainage scale in Iowa. Sediment yield of the developing ephemeral gully was partitioned from measured total watershed sediment loss, by modeling ephemeral gully development with the Annualized Agricultural Non-Point Source Pollution model (AnnAGNPS), and subtracting this soil loss value from the flume measured watershed total. Topsoil thinning in the adjacent area used to fill the ephemeral gully was calculated based on the corresponding ephemeral gully sediment yield. The effect of A horizon thickness on corn yield obtained from published literature was used to calculate the corn (Zea mays L.) yield reduction due to topsoil thinning. Ephemeral gully erosion negatively impacts farm economics in the long term and implies that soil conservation measures should be carefully designed and well maintained. However, this evidence suggests that costs associated with establishment and use of structures such as grass waterways to minimize or eliminate ephemeral gully formation will not be recuperated in the short term through yield potential maintenance.

Predicting Ephemeral Gully Location and Length Using Topographic Index Models

Abstract. Ephemeral gullies (EGs) are incised channels resulting from concentrated overland flow that often form in a similar location every year. These erosional features add to producers’ management efforts and costs. Locating EGs and predicting their length is crucial for estimating sediment load and planning conservation strategies. Since topography plays an important role in the formation of EGs, this study investigated the prediction of EG location and length in two agricultural areas (S1 and S2) in two different physiographic regions using four topographic index models: compound topographic index (CTI), slope area (SA), wetness topographic index (WTI), and slope area power (SAP). The impacts of digital elevation model (DEM) resolution, agricultural land use mask data source, and topographic model critical thresholds were also evaluated. Automated geospatial models were developed to locate and derive EG length. Results show that the SA model predicted EG occurrence and length better than other models tested. The SA and CTI model predictions had similar patterns in terms of locating EG trajectory; however, the CTI model had greater discontinuity along the trajectory. The method developed to derive length in this study was sensitive to discontinuity, so the performance of the CTI model was poor. Finer-resolution DEMs (2 m) predicted EG location and lengths better than coarser-resolution DEMs (10 m or greater). Use of actual field-level reconnaissance data instead of NASS data for agricultural land use masking decreased false negative classification by 16% or more for all models. Detailed calibration of the SA model yielded different optimal thresholds for the two study regions: TSA = 30 for S1 and TSA = 50 for S2. Topographic index models were found to be useful in locating EGs and estimating expected lengths, but site-specific calibration of the topographic index model threshold was required, which might limit the general utility of these methods.

Predicting Ephemeral Gully Location and Length Using Topographic Index Models

<abstract><title><italic>Abstract.</italic></title> Ephemeral gullies (EGs) are incised channels resulting from concentrated overland flow that often form in a similar location every year. These erosional features add to producers’ management efforts and costs. Locating EGs and predicting their length is crucial for estimating sediment load and planning conservation strategies. Since topography plays an important role in the formation of EGs, this study investigated the prediction of EG location and length in two agricultural areas (S1 and S2) in two different physiographic regions using four topographic index models: compound topographic index (CTI), slope area (SA), wetness topographic index (WTI), and slope area power (SAP). The impacts of digital elevation model (DEM) resolution, agricultural land use mask data source, and topographic model critical thresholds were also evaluated. Automated geospatial models were developed to locate and derive EG length. Results show that the SA model predicted EG occurrence and length better than other models tested. The SA and CTI model predictions had similar patterns in terms of locating EG trajectory; however, the CTI model had greater discontinuity along the trajectory. The method developed to derive length in this study was sensitive to discontinuity, so the performance of the CTI model was poor. Finer-resolution DEMs (2 m) predicted EG location and lengths better than coarser-resolution DEMs (10 m or greater). Use of actual field-level reconnaissance data instead of NASS data for agricultural land use masking decreased false negative classification by 16% or more for all models. Detailed calibration of the SA model yielded different optimal thresholds for the two study regions: T_SA = 30 for S1 and T_SA = 50 for S2. Topographic index models were found to be useful in locating EGs and estimating expected lengths, but site-specific calibration of the topographic index model threshold was required, which might limit the general utility of these methods.

AGNPS GIS-Based Tool for Watershed-Scale Identification and Mapping of Cropland Potential Ephemeral Gullies

The formation of ephemeral gullies in agricultural fields has been recognized as an important source of sediment contributing to environmental degradation and compromising crop productivity. Methodologies are being developed for assessing gully formation and gully sediment yield. The Annualized Agricultural Non-Point Source (AnnAGNPS) pollution model is an important tool for multi-temporal watershed-scale simulations because it contains the necessary components for ephemeral gully investigation, making AnnAGNPS a commonly used tool for evaluations of agricultural conservation and operation practices. AnnAGNPS requires the user to define the location of ephemeral gullies throughout the watershed, what often constitutes a time consuming task where users may not accurately locate and describe all ephemeral gully locations. Alternatively, herein a GIS-based graphical user interface is described for the automated identification of areas with high probability of forming ephemeral gullies, referred to as potential ephemeral gullies (PEGs), based on the modified Compound Topographic Index (CTI). Through the aid of a study case, PEG mouth locations along with their attributes are generated through an iterative procedure by varying different CTI threshold values (99.9%, 99.5%, 99.0%, 98.5%, and 98%). Three sets of yielded PEG mouth locations and corresponding attributes were then integrated with AnnAGNPS for assessment of the impact of potential ephemeral gullies in the watershed sediment erosion. Analysis of the spatial distribution of estimates of annual average of gully erosion identifies the sub-watersheds prone to ephemeral gully erosion, thus enhancing the applicability of AnnAGNPS to evaluate conservation practices and/or targeted interventions designed to address ephemeral gully erosion at the watershed-scale.

Quantifying interrill and ephemeral gully erosion in a small Sicilian basin interrill and ephemeral gully erosion in a small Sicilian basin

applied to document the contribution of rill-interrill erosion over the same area. Ephemeral gully formation occurred seven hydrologic years out of ten, with a frequency corresponding to 70 % of the years covered occurred seven hydrologic years out of ten, with a frequency corresponding to 70 % of the years covered by the survey and to a return period of almost 1.4 years. The mean soil loss in the seven years when EG by the survey and to a return period of almost 1.4 years. The mean soil loss in the seven years when EG was active was equal to 37.88 t ha was active was equal to 37.88 t ha –1 year –1 . The ratio between soil loss attributable to EG and total soil loss . The ratio between soil loss attributable to EG and total soil loss (SEDD + EG) resulted quite variable between erosion events accounting for 23 % to 98 % of total soil lost. EG) resulted quite variable between erosion events accounting for 23 % to 98 % of total soil lost. The overall results indicate that there are signifi cant and important differences between these two types of The overall results indicate that there are signifi cant and important differences between these two types of degradation processes elucidating the importance of EG erosion in semiarid regions. Also, the contribution degradation processes elucidating the importance of EG erosion in semiarid regions. Also, the contribution due to EG erosion emphasizes the need to extend the existing data set of soil loss by appropriate measuredue to EG erosion emphasizes the need to extend the existing data set of soil loss by appropriate measurements and fi eld campaigns. ments and fi eld campaigns.

Relationships between rainfall characteristics and ephemeral gully erosion in a cultivated catchment in Sicily (Italy)

Recent research has shown a lack of long-term monitoring for detailed analysis of gully erosion response to climate characteristics. Measures carried out from 1995 to 2007 in a wheat-cultivated area in Raddusa (Sicily, Italy), represent one of the longest series of field data on ephemeral gully, EG, erosion. The data set collected in a surface area of almost 80 ha, permits analysis of the influence of rainfall on EG formation and development. Ephemeral gullies formed in the study area were measured on a yearly scale with a Post-Processing Differential GPS for length and with a steel tape for the width and depth of transversal sections. Ephemeral gully formation was observed for 8 years out of 12, which corresponds to a return period of 1.5 years. The measurements show strong temporal variability in EG erosion, in agreement with the rainfall characteristics. The total eroded volumes ranged between 0 and ca. 800 m 3 year −1, with a mean of ca. 420 m 3 year −1, corresponding to ca. 0.6 kg m −2 year −1. Ephemeral gully erosion in the study area is directly and mainly controlled by rainfall events. An antecedent rainfall index, the maximum value of 3-days rainfall ( H max 3_d), is the rain parameter which best accounts for EG erosion. This index is used here as a simple surrogate for soil water content. An H max 3_d threshold of 51 mm was observed for EG formation. The return period of the H max 3_d threshold is almost the same as the return period for EG formation. Although a mean of seven erosive rain events were recorded in a year, EG formation and development generally occur during a single erosive event, similarly to other semiarid environments. The most critical period is that comprised between October and January, when the soil is wetter and the vegetation cover is scarce. Empirical models for EG eroded volume estimation were obtained using the data set collected at this site. A simple power-type equation is proposed to estimate the eroded volumes using H max 3_d as an independent variable. This equation shows an R 2 equal to 0.67 and a standard error of estimation of 0.79.

Characteristics and factors controlling the development of ephemeral gullies in cultivated catchments of black soil region, Northeast China

Ephemeral gully erosion is an important process in the black soil region, Northeast China and can be responsible for severe damage to agricultural lands. However, little research on gully formation in this area has been published. The study described in this paper attempted to quantify soil losses, the spatial distribution and morphology of the gullies, and the factors that control their development. Ephemeral gullies were measured in spring and summer of 2005 in two small catchments. The critical periods for ephemeral gully formation were late spring and summer in the study area. Mean soil losses due to ephemeral gully erosion were 0.40 and 0.43 kg m −2 year −1 for only croplands despite low slope gradients, and this loss is above the tolerable erosion rates of 0.20 kg m −2 year −1. The erosion rates were greater in spring because the topsoil thawed before deeper layers, reducing infiltration into the soil, and the bare vegetation cover provided no barriers to surface flow. In contrast, summer erosion occurred primarily in response to intense rain events. Development of the gullies was promoted by freeze-thaw cycles in spring and was affected by the type of agricultural operations and crops in summer. A linear regression model for the prediction of ephemeral gully length at the catchment level was established using field data, and although it did not successfully predict the length of individual gullies, it explained 55% of the variation in ephemeral gully length.

Characteristics, controlling factors and importance of deep gullies under cropland on loess-derived soils

Several studies describe the formation and importance of shallow ephemeral gullies under cropland (depth<0.8 m). Some of these gullies may develop into channels with a depth of more than 0.8 m (up to 4 m). Despite their spectacular nature, these deep gullies have not yet been studied in detail. Therefore, the objectives of this study are to analyze the characteristics and the controlling factors of these deep gullies, as well as their importance in terms of sediment production. Comparison of a dataset with 28 deep gullies, formed in the period 1985–2003 and 123 shallow ephemeral gullies formed in the period 1994–1999 in central Belgium indicates that the deep gullies have clearly different morphological characteristics compared to shallow ephemeral gullies. Several factors were analyzed to understand the formation of deep gullies. Plotting runoff contributing area versus slope of the soil surface at the gully head indicates that the topographical threshold for deep gully formation is significantly larger compared to ephemeral gully formation. Deep gullies form on short, steep valley sides and their position is strongly affected by the presence of linear landscape elements. All deep gullies incised on landscape positions with a very erodible soil horizon at shallow depth. Analysis of causative rainfall showed no significant differences in incision thresholds between rills and shallow ephemeral gullies on the one hand and deep gullies on the other hand. The relation between area-specific sediment yield in central Belgium and drainage area, indicates that the development of deep gullies contributes significantly to the sediment output of small rural catchments and causes peaks in the mean area-specific sediment yield that are up to a factor of three higher compared with catchments where shallow ephemeral gullying occurs.

Study on introducting a vegetation colony on roadcut slopes of the Siwalik region in Nepal-An experimental study at the Churiya Pass-

Although Nepal has been implementing conventional soil bioengineering measures to protect and stabilize bare roadcut slopes, it is still seeking a perennial strategy to combat the instability and destabilization of slopes. A case study was carried out at a Churiya Pass roadcut slope, which had been a serious issue for the Department of Roads(DOR), to protect and stabilize the slope from severe deterioration. The study area lies in the Siwalik region, which is very fragile and has a high erosion capacity. The DOR was unable to solve the problem through conventional soil bioengineering measures, as evidenced by the results of a revegetation project in 1993. This case study was carried out to investigate the adaptability and feasibility of a Rapid Afforestation Seeding(RAS)method by a soil seeder in Nepal. With the use of Japan’s hydro-seeder, soil-seeder technology was implemented to protect and stabilize roadcut slopes perpetually, principally by establishing a woody vegetation colony. Most of the basic materials used in the study were imported from Japan. Only half of the soil and organic matter used for preparing the carrying soil was locally prepared and arranged; it was mixed with carrying soil imported from Japan a 1:1 ratio. Local and imported plant species were used in the study. A year after the vegetation was introduced, the entire degraded study area was covered by the introduced Nepalese as well as Japanese species, showing excellent growth of more than 2 m in height. The established vegetation colony successfully prevented the development and formation of ephemeral gullies that would have resulted from concentrated flows, and protected the roadcut slope from further deterioration from severe erosion. The findings of the study show that a 3-cm growth-foundation layer is ample for growing both native and introduced vegetation in the Siwalik region.

SW—Soil and Water: Ephemeral Gully Erosion in a Wheat-cultivated Area in Sicily (Italy)

Ephemeral gully erosion is responsible for heavy damage to agricultural land and causes sedimentation and drainage network formation in most regions. Ephemeral gully length, width and depth were measured over a 5-yr period in an area of about 120 ha of heavy soils cultivated with durum wheat in Sicily (Italy) in order to quantify the soil losses and to examine, by statistical analysis, the relationships between this kind of erosion, precipitation and the characteristics of the watersheds. Ephemeral gully formation was observed for 4 yr out of five in the study area. A mean length of about 36 m ha −1 yr −1 and mean soil losses of 3·3 m 3 ha −1 yr −1 were measured. The channel depth reached a maximum value (>1 m) 3 yr out of four. In the examined soils, this kind of erosion occurs when the moisture content of the soil is high: regression analysis indicates that the soil moisture content can be expressed by the amount of precipitation for 3 days. In the observation period, the minimum 3-day rainfall which gave rise to channel formation was 51 mm; since the 51 mm return period is less than 2 yr, the risk of erosion is high. Mean depth and width, which are the channel characteristics that vary the least between the different years, seem to be controlled by the soil, crop and field characteristics, whereas the precipitation regime seems mainly to influence their number and length. Regression equations were performed to estimate ephemeral gully surface area and soil losses measuring the length alone. Length measurement by the global position system is sufficiently accurate and fast. The influence of watershed surface area and length on ephemeral gully erosion indicates that a reduction in field area and length may be an effective measure to reduce this kind of erosion.

CHARACTERISTICS OF ACTIVELY ERODING EPHEMERAL GULLIES IN AN EXPERIMENTAL CHANNEL

The formation of ephemeral gullies can significantly increase soil losses from agricultural lands and severely impact farm productivity, yet few data exist on the physical characteristics of actively eroding gullies. The objectives of the current study were to examine the time variation of gully morphology and sediment load in response to a range of overland flow discharges and the impact of soil moisture content and soil density on erosion rates. Preformed ephemeral gullies were constructed at field scale in a large experimental channel using the same cohesive soil but at two different moisture contents and bulk densities. For the bed with relatively high soil moisture content and bulk density, clear-water flows caused low rates of erosion, detachment-limited flows prevailed, and bed degradation was uniform along the flume. For the bed with relatively low soil moisture content and bulk density, comparable clear-water flows caused high rates of erosion, both detachment-limited and transport-limited flows prevailed, and bed degradation was greater in the upstream reaches. In both experiments, erosion caused the gullies to incise, to significantly increase gully bottom width, and to steepen gully sidewalls. These results compare favorably with field studies of ephemeral gullies, and the hydraulics and sediment transport processes observed are similar to those reported for actively eroding rills.