Enumerating the relative proportions of soil losses due to rill erosion processes during monsoon and post-monsoon season is a significant factor in predicting total soil losses and sediment transport and deposition. Present study evaluated the rill network with simulated experiment of treatments on varying slope and rainfall intensity to find out the rill erosion processes and sediment discharge in relation to slope and rainfall intensity. Results showed a significant relationship between the rainfall intensity and sediment yield (r = 0.75). Our results illustrated that due to increase in rainfall intensity represent the development of efficient rill network while, no rill was found with a slope of 20° and a rainfall intensity of 60 mm·h-1. The highest rill length was observed in plot E with 20° slope and 120 mm·h-1 rainfall intensity at 360 minutes. Positive and strong correlation (R2 = 0.734, P < 0.001) was observed between the cumulative rainfall intensity and sediment discharge. A longitudinal profile was delineated and showed that the depth and numbers of depressions amplified with time and were more prominent for escalating rainfall intensity for its steeper slopes. Information derived from the study could be applied to estimate longer-term erosion stirring over larger areas possessing parallel landforms.
Rainfall simulation is widely used by hydrologists [1-4], geomorphologists [5-7] and soil scientists [8,9] are involved in theoretical research and its applications to field problems, providing some possibility for control of a critical variation. It permits precise replication of storm events and sequences which recur naturally only over a prolonged period. Simulators have evolved in response to precise research requirements and to local technical, financial or logistic conditions [
Alternatively, flume experiments have added great attention to our understanding of the complex dynamics of the fluvial system [
The experiment was conducted in the Laboratory of Geography and Environment Management, Vidyasagar University, West Bengal, India. A small runoff plots (1 × 1.5 × 0.30 m) was used with a rainfall simulator (
the left bank of Kasai River in the city of Medinipur, West Bengal. The soil samples were packed in the plot, with a bulk density of 1.13 to 1.15 g∙cm−3. During the packing process, a static weight method was used to pack the soil uniformly in the box; the packed soil surface was smoothed manually with a rake. After the initial rainfall, the packed soil was saturated and allowed to equilibrate for the least 48 hours, while the plot remained in a horizontal position to ensure a uniform and homogeneous soil moisture contents close to field capacity.
A tripod mounted Guelph Rainfall Simulator followed by Tossell et al., [
The treatments were carried out on three different slopes (e.g., 26.79˚, 36.40˚ and 46.63˚), each with three varying levels of rainfall intensity (e.g., 60, 90, and 120 mm∙h−1) (
Each test was carried out after 7.00 hours of the initial rainfall and pre-wetting subsequent the soil grounding. The opening time of the simulated rainfall, the time when runoff reached the outlet of the plot, and the time when rill initiation occurred were documented from the experimental plot (
buckets were weight before and after decant of water. The remaining water and sediment were transferred into containers that were dried in ovens at 105˚C for at least 24 hours, or until the samples were completely dry. The mass of the sediment was then measured and used to calculate the sediment concentration.
The observations were made during and after the experiment including photographs, the rill formation and video-recording the change in rill morphology followed by Yao et al., [
The rainfall intensity was detained constant during the test and sediment and runoff samples were collected at the outlet of the discharge panel sheet every minute during the first 60 minutes. Variation in rainfall intensity and associated runoff affect the soil detachment and sediment concentration.
Mean total runoff did not vary significantly between the different treatment (F-test p < 0.000), both with regard to slope and rainfall intensity. However, important dissimilarities between three groups of experiments were recognized when applying the same test to mean total sediment yield. By varying slope at steady rainfall intensity of 90 mm∙h−1, cumulative sediment yield after 210 mm was appreciably diverse for the treatment with 15˚ slope (
ment yield consisted of the experiment with 120 mm∙h−1 and 20˚ slope. Moreover, our results also indicated that rainfall intensity had a stronger effect in sediment yield than the amends in slope for the given treatments. This study is also corroborated with the previous study conducted by Favis-Mortlock et al. [
Additionally, a scatter plot has been drawn to estimate the relationship of cumulative sediment yield after 90 minutes experimental time increased exponentially with cumulative runoff when the rainfall intensity increased (
An observation has been made for 7 hours period in five experimental plots and in different slopes to understand the rill erosion process in each experimental plot. In the early stage of the experiment, seepage lines begin to appear on the lower part of slope within one hour. It also found that the splash of soil particles was predominant by the raindrop impact on the slope. Subsequently, as the surface flow began to generate at the lower part of slope, the seepage line gradually moved up, and the sheet erosion and rill erosion was started by transported sand silt and clay through the surface flow and channels (
As the sheet erosion continued, many small rills appeared on the lower part of the slope. Some of the them increased in size, and grow into small channels or first stage of rill by concentrated flow. These rills generally spared upward to the slope through spreading their plan size, branching and bifurcation. Rills growth was very unstable became a channel sometimes jointed another one, or a rill which had been just formed was buried by the sediment yield, and the time at which rill generally began, depends on the rainfall intensity and slope gradient (
Rill density is the number of rills per unit width. Hansen et al., [
that sheet and splash erosion were accountable for the bulk of erosion mostly for the low-intensity treatment. However, a simple correlation was calculated between the cumulative rainfall intensity and sediment discharge (
A longitudinal profile was delineated to illustrate the changes in plane pattern of rill over time of experimental plots (
Five experiments were conducted on three slope gradients and three rainfall intensity using experimental methodologies. The results of this study challenge the assumption often used in hydrologic and erosion models for better prediction of sheet erosion or actives rill erosion. This result illustrated here the interactions of slope gradient, rainfall intensity, erosion in the formation of rills and network. Rills often act as sediment sources and the dominant sediment and water transport mechanism of upland slopes. It was found that during simulated rainstorms, the measured amount of interrill erosion in the sediment progressively declined as that of rill erosion increased. Since rill erosion sources comparatively greater soil loss than interrill erosion, the outcome of the study might be useful to determine when rill erosion becomes a significant contributor to overall soil losses and aids to take the necessary action for its control.