Rill Formation Research Articles

ENVIRONMENTAL EFFECTS OF APPLYING COMPOSTED ORGANICS TO NEW HIGHWAY EMBANKMENTS: PART III. RILL EROSION

Control of stormwater runoff and soil erosion on highway construction sites is a concern for state departments of transportation and municipalities. Composted organics are viewed as an alternative approach to improve construction site soils and to reduce runoff and soil erosion. The objective of this study is to evaluate the use of blanket-applied composted organics on rill erosion as compared to soils. Rill erosion was measured on three composted organics applied at 5 and 10 cm depths, a topsoil treatment (15 cm application), and the existing soil (control) on a highway embankment with a three-to-one sideslope (33%). Treatments were tested using rainfall simulation at a target rate of 100 mm/h and simultaneously adding five inflows at the top of the rill on both vegetated and unvegetated plots. Rill erosion on blanket-applied compost treatments was measured, and the usefulness of the shear stress model for predicting rill erosion on compost-treated areas was assessed. Rill erodibilities and critical shear values were calculated for all treatments using the shear stress model that was originally developed for soil. Rill erodibilities were higher on topsoil-treated plots than on control and compost-treated areas. Yard waste had significantly lower rill erodibility than all other compost and soil treatments. There were no significant differences between critical shear values for the composts and soil. Yard waste compost exhibited greater resistance to rill formation than the biosolids and bio-industrial composts or the two soils. Low R2 values for compost erodibility and critical shear suggest that the shear stress model used in this analysis is not well suited for use with composted organics. Detachment caused by flotation of low-density particles, and bridging caused by coarse particles lodging farther down the slope, are believed to be two rill erosion mechanisms in compost that the shear stress model does not adequately address.

Rill density prediction and flow velocity distributions on agricultural areas in the Pacific Northwest

This research focused on rill formation, rill density, and associated flow velocity distribution in rills at the field level and with different tillage treatments in the inland Pacific Northwest. The study was conducted by applying flow at three different rates under winter conditions, which provides the greatest potential for rill formation. The following tillage treatments were tested: chisel plow, moldboard plow, conventional seedbed tillage, and untilled stubble from no-till seeded peas. Twelve plots of 7.3 m 2 were established for each tillage treatment and flow applied on them. The conventional seedbed tillage plots were the most susceptible to rill formation, with one or two resultant rills per meter. On the opposite, the untilled stubble plots did not form rills in most of the cases. Increase in applied flow, soil moisture content, and slope appeared to favor rill formation, while the effect of random roughness and residue was the opposite. By including these variables, an equation for predicting rill density was developed. Rill flow velocity distributions were clearly different for each tillage treatment. Higher flow velocities implied the formation of more rills. At least 0.35 m 2/m 2 of residue cover was necessary to reduce in a half the average flow velocity in the unfilled stubble plots respect to the conventional seedbed plots. Therefore, the use of untilled stubble tillage system is recommended to minimize soil erosion. These results provide information for advancing the understanding of the rill erosion process.

Assessment of soil erosion indicators for maize-based agro-ecosystems in Kenya

Measuring soil loss is costly, must cover a range of field situations, is not standardized, and is season dependent. In addition, use of sparse soil loss data (from other studies) compromises the integrity of many erosion models. Easily assessable soil erosion indicators to monitor the cumulative effect of erosion between tillage/weeding and harvesting called eroding clods, flow surfaces, pre-rills, and rills were surveyed directly after the 1995 rainy season in the Taita Taveta district of Kenya, to assessed the utility of each indicator. Their incidences were modeled using CPA. In the area, 70 maize plots in 11 map units, having considerable variation in altitude, land cover, rainfall, and geomorphology, were surveyed. Soil loss was considered variable between plots due to differences in surface soil, land cover, infrastructure (trash lines, grass strips, and Fanya-juu), crop management, slope, and map unit. The eroding clods indicator proved of little significance because the initial clods cover was unknown; the indicator probably relates better to soil erodibility then to soil loss. Flow surfaces, formed during erosive showers, were less present on fields with a higher ground and canopy cover, if the area of eroding clods was high, and if the topsoil had no loam which reduces chances of sealing; no impact of infrastructure, tillage, and weeding were detected. Fewer pre-rills were present where the fraction of groundcover was high, where Pigeon Peas were not grown (they cause micro-relief and concentrated flows), where weeding ended late (time effect), where more flow surfaces occurred, where Fanya-juu was constructed (less steep slopes), where the top-soil contained little sand (less sediment entrainment), and where maize was intercropped with vegetables (positive canopy cover effects). The model was not map unit specific and had an Adjusted R 2 of 67%. The log-linear relationship indicates that combined positive conditions exponentially reduce the occurrence of pre-rills. The “pre-rill” indicator related best to management-affected site conditions and seems to reflect best the cumulative effects of soil loss over time. Rills were found at 18 sites located in drier areas on sandy–clay soils. The model suggested more rills if the topsoil contains no silt; this makes the soil susceptible to compaction, peptisation when wet, and rill formation.

Longitudinal velocity patterns and bed morphology interaction in a rill

AbstractPresent‐day understanding of rill dynamics is hampered by a lack of detailed data on velocity distributions in rills. The latter are difficult to collect with traditional techniques due to the very low water depths and the relatively high flow velocities in rills. The objectives of this paper were to investigate the feasibility of miniaturized acoustic Doppler velocimeter (mADV) measurements in rill flow and to explore longitudinal variations in flow velocities and their relationship with rill bed morphology. Detailed data on longitudinal flow velocity were required to achieve these objectives.A 1·8 m long rill was formed freely in a flume at 5° slope and 0·001 m3 s−1 discharge. Rill topography was characterized by an alternation of steps and pools. The flume surface was then fixed to preserve rill roughness. A topographical scanning of the entire flume surface was made. Velocity was measured with a mADV along the rill, and at different depths. Flow depth in a longitudinal direction was also measured using an elevation gauge.A strong relationship exists between rill topography and flow hydraulics. Over steps, flow was unidirectional and rapidly accelerating until a threshold Froude number (Fn) value between 1·3 and 1·7 was reached and a hydraulic jump occurred leading to the formation of a pool. In the pool, the flow pattern was multidirectional and complex. The flow was subcritical when leaving the pool and accelerated over the next step until the threshold Froude number value was again reached. Energy loss in the rill was concentrated in the pools, mainly due to the action of a hydraulic jump. This mechanism of energy dissipation appeared to be an essential factor in rill formation and bedform evolution. Copyright © 2004 John Wiley & Sons, Ltd.

Rill Formation and Development of Rill Networks on Sloping Reclaimed Fields during a Short Period

Rill Formation and Development of Rill Networks on Sloping Reclaimed Fields during a Short Period

Polyacrylamide Effect on Infiltration and Erosion in Furrows

Surface sealing and crusting are important factors affecting runoff and erosion in many cultivated soils. The objective of this study was to evaluate the effects of low rates of surface-applied anionic polyacrylamide (PAM) on surface sealing and crusting, water infiltration, and soil erosion. A series of experiments was conducted on a Cecil sandy loam soil (clayey, kaolinitic, thermic Typic Kanhapludult) in ridge-furrow-type field plots (3.5 by 0.92 m). Polyacrylamide solutions containing 1 kg solids m−3 and 2.5 mol CaSO4 m−3 were sprayed onto dry soil surfaces at 15 and 30 kg ha−1 rates with two replicates each. Three simulated rains, 31 min each, were applied at an intensity of 85 mm h−1 at 2-wk intervals. Final infiltration rates were 30 mm h−1 for the control treatment for all three rains and were >85 mm h−1 for the first rain and 45 mm h−1 for the two following rains for the PAM treatments. Total soil loss of the control was 1.62 kg m−2 for the first rain, while the average soil loss of the two PAM treatments was only 0.03 kg m−2. For two subsequent rains, although the differences were narrowed, soil loss from PAM was 48 to 66% less than from the control. The percentage of sediments >0.5 mm in the PAM treatments was 45% greater than in the control, indicating high aggregate stability with PAM addition. The sediment reduction was attributed to the significant reduction of runoff and the prevention of rill formation due to PAM addition. Based on this study, surface application of PAM at a rate of 15 kg ha−1 controlled surface sealing and crusting and therefore reduced runoff and erosion.

Physical and Chemical Crusting Processes Affecting Runoff and Erosion in Furrows

Surface sealing and soil crusting increase runoff and erosion dramatically on many soils. The rate of this increase may depend on the extent and predominant processes of soil crusting. The objective of this study was to evaluate the effects of soil crusting processes on infiltration and erosion, particularly rill erosion. Six field plots (3.5 by 0.9 m) with V-shaped furrows with sideslopes of 0.2 m m -1 and gradients of 0.11 m m -1 were established on a Cecil sandy loam (clayey, kaolinitic, thermic Typic Kanhapludult). Treatments included control, gypsum (surface-applied, 5 Mg ha -1 ), screen cover, and the combination of cover and gypsum. Two consecutive rains at an intensity of 90 mm h -1 were applied to each treatment, and soil surface was allowed to dry between rains. Statistical analyses showed the main effects of cover and gypsum, as well as their interaction, significantly increased final infiltration rate (FIR) on this soil. During Event 1, FIRs were increased by 26% for either cover or gypsum treatment and by 132% for the combined treatment. Although the effectiveness of all treatments was reduced during Event 2, the combined treatment still showed 56% increase over the control treatment. As a result of runoff reduction, overall soil loss from the two events was reduced by 64, 28, and 88% for the cover, gypsum, and combined treatments, respectively. Minimizing seal formation by either cover or gypsum delayed rill formation and reduced rill erosion to a similar extent, but the combination of the two was much more effective. For this soil, both chemical (dispersion) and physical (raindrop impact) forces, as well as their interaction, are critical in crust and seal formation.

Using rill/interrill comparisons to infer likely responses of erosion to slope length: implications for land management

With the release of the Revised Universal Soil Loss Equation (RUSLE) there is potential to consider a range of responses of erosion to increasing slope length. This paper presents data to illustrate commonly observed effects of increasing overland flow on erosion processes and erosion rates, and considers the application of the data to specifying land management strategies and forms of vegetative cover most suited to particular soils. It also discusses a methodology for assessing relevant slope length factors for the RUSLE based on rill/interrill susceptibility. Three basic responses to slope length are noted: (i) little increase in erosion per unit area with increasing length, due to either the failure of rills to develop for the range of overland flows considered, or rill formation at very low hows with no further increase in erosion rates as flow rates increase; (ii) moderate increase in erosion per unit area with slope length associated with slight rill development; and (iii) large increases in erosion per unit area with slope length as rilling develops strongly. These responses have significance for the relative importance of surface and contact cover (and therefore, for the plant species grown and/or residue management strategy adopted), and for the use of contour banks to reduce slope length.

The influence of aspect on runoff and soil loss in a Mediterranean burnt forest (Spain)

In order to evaluate the soil loss in a burnt forest and the role played by slope orientation in erosion, a study has been carried out in the Montserrat area (NE Spain) affected by a fire in summer 1986. Previous geomorphological surveys allowed us to propose the hypothesis that slope orientation acted as a macrofactor or integrating factor in erosion control. Aspect controls temperature, moisture and water supply and then vegetation and soil development. The evaluation was determined by monitoring two experimental plots 250 m apart developed on equal substrate and slope but one facing north and the other facing south. The plots, with a surface area of 200 m 2 are equipped with collecting and sampling units (Multi-slot divisors) and storage tanks. The results (August 1987 – December 1988) confirm the contrast in runoff and soil losses according to slope orientation (2176 g/m 2 south-facing plot and 352 g/m 2 north-facing plot). This different erosive response is mainly due to: a) the state of the vegetation and soil development before the fire, b) the differences in vegetation recovery after fire. The north-facing slopes had a denser plant cover and thicker soil than the south-facing ones. After the fire the north-facing slopes were covered by a thicker blanket of ashes and burnt plant debris and, later, more vegetation giving the soil higher infiltration capacity and resistance. Moreover, the two major events displayed different behaviour according to slope orientation. The first of those events, due to the conditions on each slope (higher or lower protection and available erodible material) gave rise to a change in the threshold conditions: a) the rill formation on the south-facing plot enhanced the flow concentration and sediment transport (lowering of threshold) in the second event and b) on the north-facing one, the lack of rills and the decrease in erodible material caused by the first event hindered subsequent erosion (threshold rise). Finally, the progressive recovery of spontaneous vegetation caused erosion to drop, reaching low rates in 1988 (22 g/m 2 and 2 g/m 2 on each plot).

Hydraulic conditions for rill incision under simulated rainfall: A laboratory experiment

AbstractA series of controlled laboratory experiments were conducted in order to obtain precise data on the hydraulic and sediment transport conditions during rill formation. Tests were carried out using a crusting‐prone binary mixed soil in a 15 m long flume at an average slope of 0·087 under simulated rainfall. Rainfall intensities varied from 30–35 mm h−1 and developed about 70 per cent of the kinetic energy of natural rainfall of similar intensity.Runoff and sediment discharge measured at the downstream weir were strongly influenced by rill forming processes. Essentially, rill incision reduced runoff discharge as a result of increased percolation in rill channels but increased sediment discharge. Secondary entrainment processes, such as bank collapse, also increased sediment discharge at the weir. Knickpoint bifurcation and colluvial deposition, however, decreased sediment discharge. Rills always developed through the formation of a knickpoint. The critical condition for knickpoint initiation was the development of supercritical flow and waves which mould and incise the bed. Prior smoothing of the soil surface by entrainment and redistribution of sediment facilitated supercritical flow. Statistical analysis showed that hydraulic and sediment transport conditions differed significantly in rilled and unrilled flows. The relationship between sediment discharge, rill erosion, and flow hydraulics was found to be nonlinear, conforming to a standard power function in the form y = axb. Rills were also associated with significantly increased sediment transport capacities. However, rill initiation was not clearly defined by any specific hydraulic threshold. Instead, rilled and unrilled flows were separated by zones of transition within which both types of flow occur.

Soil Dispersibility, Rain Properties, and Slope Interaction in Rill Formation and Erosion

AbstractSoil erosion increases with slope steepness. We hypothesized that the rate at which short‐slope soil erosion increases with slope steepness depends on the prevailing erosion mechanism, which in turn depends on soil dispersibility and rain properties (impact energy of drops and water quality). Soil dispersion, as a function of exchangeable sodium percentage (ESP) and water quality, was determined by shaking soil samples in deionized water (DW) or tap water (TW). Clay dispersion increased with increases in soil ESP and was prevented by the electrolyte concentration in TW. We studied the effect of soil ESP, water quality, and the impact energy of rain on soil erosion while maintaining similar runoff. To do so, we first exposed the soil samples to DW rain on a 5% slope until a surface seal developed. Then we increased the slope to 35% and changed the water quality and impact energy of the rain. Runoff volumes were unaffected by rain properties at the 35% slope. Soil losses increased with increases in the ESP of the soil. Soil losses varied with rain properties in the following order: DW rain > TW rain = DW rain with low energy (mist) > TW mist. Rills were formed by both DW rains (high impact energy and mist). The extent of rilling increased with soil ESP. No rills were formed by TW rains. Under dispersive conditions (sodic soils and DW), runoff was sufficient to initiate rilling and soil losses increased sharply with slope.

Hillside Farming, Soil Erosion, and Forest Conversion in Two Southeast Asian National Parks

Relationships between soil erosion on hillside farms and forest conversion to farmland in adjacent national parks were examined in the Bayhang watershed near Leyte Mountains National Park, Philippines, and the Sungai Ning watershed near Kerinci- Seblat National Park, Indonesia. A random sample of hillside farms revealed widespread evidence of accelerated soil erosion in both watersheds, including splash and sheet erosion, and rill and gully formation. Erosion under line transects and on enclosed runoff plots revealed mean soil losses of 422 t/ha during the first six months of cultivation on recently cleared farms in Bayhang and 3.8 t/ha during the cropping year on continuously cultivated farms in Sungai Ning. Analysis of eroded sediments and uneroded soils revealed erosion-induced reductions in soil productivity. Soil erosion and land degradation were found to contribute to forest conversion in both national parks. The farmers' response to land degradation in Bayhang was to clear forest for new farms in Leyte Mountains National Park, while farmers in Kerinci replaced nutrient-demanding crops with cassava, and cleared forest for new farms in Kerinci-Seblat National Park. Potentially sustainable and appropriate soil conservation and economic development activities for use in the two watersheds are reviewed.

Rilling of hillslopes reclaimed before 1977 surface mining law, Dave Johnston Mine, Wyoming

AbstractThe erosion of hillslopes reclaimed following the surface‐mining of coal is an important geomorphologic concern. However, progress in the design of post‐mining topography and its hydrologic response has been hampered by the paucity of research focusing on the propensity of rill formation on these disturbed surfaces. This investigation is intended to partially rectify this situation through the development of regression equations for the prediction of rill frequency and magnitude based upon site characteristics. Rill width can be estimated using soil bulk density, hillslope age, and hillslope length with a standard error of 0.152 log10 units at this location. Rill depth can be estimated using soil shear strength, hillslope length, and hillslope age with a standard error of 0.114 log10 units. Rill length can be estimated using hillslope length, percent silt in the soil, hillslope age, Bouyoucos Clay Ratio, and soil bulk density with a standard error of 3.515 m. Rill frequency can be estimated using soil bulk density, Bouyoucos Clay Ratio, soil compaction, soil reaction (pH), and hillslope age with a standard error of 0.241 rills/m. The cross‐product of rill width times depth can be estimated using soil shear strength, hillslope length, hillslope age, and soil bulk density with a standard error of 0.260 log10 units. These results must be tested further under various environmental conditions. Nevertheless, prediction of rill formation seems to be a problem capable of solution.

Slope Gradient Effect on Erosion of Reclaimed Soil

ABSTRACT SOIL erosion from areas of newly reclaimed surface mines damage the surrounding environment and reduce the value and productivity of the reclaimed land. Newly reclaimed soil on sloping land is very susceptible to erosion due to the lack of vegetation and slope steepness resulting from reclamation. To quantify the effect of slope steepness on soil erosion from newly reclaimed land, a rainfall simulator was used to erode replicated plots of reclaimed A horizon soil on slopes ranging from 5 to 16% at two surface mines. The objective of this research was to quantify the effect of slope steepness on soil loss, flow velocity, and rill formation using regression to analyze collected runoff data. A linear slope factor was developed from the data of both sites for use in the Universal Soil Loss Equation (USLE). It differed sharply from the curvilinear relation suggested for use in the USLE for slopes greater than 10%. The factors compared favorable for slopes of less than 10%. Surprisingly little correlation was established between slope steepness and flow velocity. A positive linear correlation was revealed between the length of observable rills and slope steepness.

The identification of four stages during micro‐rill development

AbstractSeparation of rill and inter‐rill erosion is required in many of the soil erosion models currently being developed. The feasibility of basing the separation on the hydraulic properties of the flow and resultant sediment production is examined in a laboratory simulation of rill initiation and development. Four stages are identified in the process of rill formation; these are sheetflow, flowline development, micro‐rills, and micro‐rills with headcuts. There are significant differences in terms of flow characteristics between the stages, especially between sheetflow and flowlines, indicating the promise of this method for making a more precise distinction between rill and inter‐rill erosion.

Postfire Succession in a Sierran Subalpine Meadow

A lightning-ignited fire in 1977 burned a subalpine meadow in Kings Canyon National Park, California. Vegetation establishment and succession were studied for 4 years after the fire. Herbaceous cover increased from 2.3%, immediately after burning, to 123.8% in 1981. Broadleaf species were dominant the 1st year with grass and graminoid species becoming dominant in later years. The fire also resulted in some soil puddling and rill formation although no catastrophic changes were observed.

Use of a Versatile Experimental System for Soil Erosion Studies

AbstractA laboratory facility for the study of soil erosion is described. Rainfall from a modular system supplied raindrops at near terminal velocity to prepared soil beds set in a flume with slope adjustable up to 30%. A comparison was made of erosion under overland flow alone and storm rains of the same intensity (discharge), but different energy levels. Raindrop impact in runoff flow was a powerful agency in promoting soil transport and inhibiting rill formation. Bed‐load movement was important in the transport of sand grains, even where the runoff was disturbed by raindrops.