Effects of rainfall patterns on runoff and soil erosion in field plots

Soil erosion processes during a storm are strongly affected by intra-storm variations in rainfall characteristics.Four storm patterns,each with a different rainfall intensity variation were separated.The storm patterns were:(1)increasing rainfall intensity(2)increasing then decreasing intensity(3)decreasing intensity(4)decreasing then increasing intensity.After each erosive rainfall(12 events),Runoff and suspended sediment samples were collected in each plot's tank which is located on hillslopes of the basin of Khamsan.Main storm characteristics and soil losses were plotted and equation of the line of best fit were selected.Analysis of variance(ANOVA)was used to determine response of runoff and soil erosion to storm patterns.Results showed that in lower rainfall intensities a linear function fits the relationship between soil loss and rainfall intensity whereas this function tends to be non-linear at higher intensities.Also a strong non-linear relationship was found between different quartiles of storm and soil loss.Statistical analysis revealed significant differences in total runoff,soil loss and sediment concentration across four storm patterns(P<0.001)but no differences in the runoff coefficient.In particular,storms with increasing rainfall intensity yielded highest quantities of eroded sediments,total runoff and highest sediment concentrations followed by increasing then decreasing,decreasing then increasing and decreasing intensity,respectively.

几种土壤的细沟侵蚀过程及其影响因素

通过间隔为11h的二次人工模拟降雨和冲蚀槽试验研究了10种土壤的侵蚀过程,发现在第2次降雨中大多数土壤出现了细沟侵蚀形式。采样微形态观察发现,在第1次降雨中形成结皮的土壤在第2次降雨中出现了细沟侵蚀;产流产沙观测发现所有出现细沟侵蚀的土壤在第1次降雨中径流含沙量逐渐减少,而第2次降雨中有一个先剧增后减少的过程。土壤理化分析及多元逐步回归分析结果表明,土壤颗粒组成、有机质含量、铁铝含量等因素对细沟侵蚀的影响表现不明显,而与土壤团聚体有关结构指标、细沟侵蚀、产流产沙速率及总量呈显著相关关系。分析表明,团聚体分散度、崩解速率与渗透系数之比两个指标能较好地预测细沟侵蚀发生的可能性,同时也能很好地预测侵蚀产沙量。

Influence of vegetation cover and other sources of variability on sediment and runoff response in a burned forest in South Korea

Post-fire field measurements of sediment and run off yield were undertaken in natural rainfall event-basis during five rainy months in Korea on a total of 15 small plots: four replica burned unseeded plots, six replica burned seeded plots, and five replica unburned plots. The main aim was to evaluate the effects of vegetation recovery and spatial distribution patterns on sediment and runoff response between and within the treatment replica erosion plots. Sixyears after the wildfire, total sediment and runoff yield in the burned unseeded plots with 20%-30%vegetation cover was still 120.8 and 20.6 times higher than in the unburned treatment plots with 100%ground cover, 8.3 and 6.7 times higher than in the burned seeded plots with 70%-80% vegetation cover,while only 1.6 and 2.0 times higher than in the burned seeded plots with 50%-60% vegetation cover,respectively. The differences in sediment and runoff yield between the treatment plots was proportional to total vegetation cover, distance of bare soil to vegetation cover, magnitude of rainfall characteristics and changes in soil properties, but not slope gradient.Three out of the six within-treatment pairs of two replica plots showed large differences in sediment and runoff yield of up to 6.0 and 4.2 times and mean CV of up to 99.1% and 62.2%, respectively. This was due to differences in the spatial distribution patterns of surface cover features, including aggregation of vegetation and litter covers, the distance of bare soil exposed to vegetation cover closer to the plot sediment collector and micro topographic mounds and sinks between pairs of replica plots. Small differences in sediment and runoff of only 0.9-1.4folds and mean CV of 8.6%-25% were observed where the within-treatment pairs of replica plots had similar slope, total surface cover components and comparable spatial distribution pattern of vegetation and bare soil exposed surface covers. The results indicated that post-fire hillslopes undergoing effective vegetation recovery have the potential to reduce sediment and runoff production nearer to unburned levels within 6-years after burning while wildfire impacts could last more than 6-years on burned unseeded ridge slopes undergoing slow vegetation recovery.

Effects of rates and time of zeolite application on controlling runoff generation and soil loss from a soil subjected to a freeze-thaw cycle

Many factors such as freeze-thaw(FT)cycle influence soil behavior.Application of soil amendments can play an important role on runoff time commencement(RT),volume(RV)and soil loss(SL)on soils subjected to FT cycles.However,limited studies have been documented on this subject.The present study was therefore carried out under rainfall simulation circumstances to investigate the effect of different rates of zeolite ap-plication to control the effects of FT on basic hydrological variables such as runoff production and soil loss.Towards this attempt,the effect of application of different rates of 250,500 and 750 gm^(-2) of zeolite applied before,during and after the occurrence of FT cycle on RT,RV and SL was assessed in a completely randomized design.Treatments were set up in two categories viz.control(without zeolite application),and three rates and times of zeolite application in small 0.25 m-experimental plots in three replications.The results showed that application of zeolite had significant effects on hydrological behavior of soil induced by FT cycles.Ap-plication rate of 750 gm^(-2) prior to FT cycle increased RT and reduced RV and SL at rates of 644%,68% and 91%,respectively.The results also verified that zeolite could successfully mitigate the impacts of FT cycle on the main soil hydrological variables of soil profile induced by FT cycle.It is accordingly recommended to employ zeolite as an effective amendment to control soil erosion in steep and degraded rangelands where surface soil is exposed to rainfall and runoff.

Runoff and soil loss responses of cultivated land managed with graded soil bunds of different ages in the Upper Blue Nile basin,Ethiopia

Background:In view of a wide range of on-site and off-site impacts of soil erosion,different soil and water conservation measures have been implemented mainly over the last two decades in the Gumara watershed and Ethiopia at large.But their effects have not been sufficiently documented,and maintenance of structures received very little attention.This study investigated the effectiveness of graded soil bunds of zero and 11 years of age in reducing runoff and soil loss.Six hydrologically isolated experimental runoff plots(three treatments×two replicates)were prepared to observe rainfall,runoff,and sediment concentrations in the 2019 summer rainfall season(covering approximately 70%of the annual rainfall).Results:Newly constructed soil bunds reduced runoff by 34.94 and 25.56%compared to the old and non-treated counterparts,respectively.Similarly,59.6 and 48.3%soil loss reductions were observed.The amount of soil loss in non-treated plots was twice that from the new plots and even 1.6 times higher than that from the old-graded soil bund treatments.The rate of soil loss in the new-and old-graded soil bund-treated and non-treated plots was 23.5,45.6,and 58.1 t ha^(-1) year^(-1),respectively.However,the effectiveness of the old soil bunds was much lower(only^(-1)2.6 and−21.7%in runoff and soil loss,respectively)than its new equivalent.Graded soil bunds,in its new form,reduced runoff,runoff coefficient,and soil loss significantly(P<0.05).Regardless of the treatments,from the start of the rainy season to the end,runoff and runoff coefficient showed an increase,but sediment concentration decreased.Newly constructed soil bund is the most effective in reducing runoff and soil loss.Conclusion:Graded soil bunds reduced runoff and soil loss significantly,but the rate even in the treated plots was very high when compared to both the soil loss tolerance(1-6 t ha^(-1) year^(-1))and formation rate(10-14 t ha^(-1) year^(-1))estimated for the area.Hence,these structures need to be supported by other measures such as grass strips,agroforestry,and percolation ditches,for better results.Besides,regular maintenance by either removing sediments from bund furrows or increasing the bund height is recommended for sustained reduction of runoff and soil loss.