Methodology for the Calculation of the Runoff Coefficient with the Arrangement Tirado

For this research work, an adequate methodology was sought for the calculation of the runoff coefficient with the Tirado arrangement. To achieve this, first, the variables that affect the runoff coefficient were identified, then the model was described with the Tirado arrangement, and as a third part for the calculation of the runoff coefficient, the Tirado model is proposed. From the theory for the calculation of the runoff coefficient, the equation of the weighted coefficients and the expression of Nadal were manipulated, resulting in the following relationship , considering this as the expression for the arrangement Tirado. The expression is tested with different intensities, the magnitudes correspond to 150, 200, 250 and 300 mm/hrs, resulting in runoff coefficient 0.82, 0.87, 0.89, 0.91 respectively. This means that, the higher the intensity, the runoff coefficient will be higher, logically the characteristics of the basin affect that this coefficient has variation in the space studied.

Is the runoff coefficient increasing or decreasing after ecological restoration on China’s Loess Plateau?

The“Grain for Green”project(GGP)was launched in 1999 on China’s Loess Plateau to reduce soil erosion,which had far-reaching impacts on the local eco-hydrological processes.In this study,we use monthly runoff depth and precipitation datasets spanning 1961 to 2015 for 16 primary basins of the plateau to reveal changes in runoff generation capacity before and after the GGP.We use a Budyko-based elasticity method to calculate the runoff depth(R_(1))and runoff coefficient(C_(1))exclusively attributable to land use/cover change.Results indicate that the mean annual runoff coefficients(Co)decline by 26%—76%from the periods 1961—1999 to 2000—2015.The annual observed runoff depth(Ro)and C_(0)for 75%of basins show significant downward trends during 1961—1999;after the implementation of the GGP,both annual Ro and annual Co for over 50%of basins show upward trends.The study further finds that the increase of erosive rainfall during the period 2000-2015,whose mean increasing rate reaches 4.6 mm/year,is the main reason for the upward trends of Ro and Co.After removing the effect of precipitation variation during this period,we find that 11 out of 16 basins show decreased trends for Cj,with the downward rate between 2.4%and 6.0%per year.The reduction rate in semi-arid areas is about four times the rate in semi-humid areas.The results remind us to consider the carrying capacity of local water resources when implementing soil and water conservation measures across the Loess Plateau.

Determination of urban runoff coefficient using time series inverse modeling

Runoff coefficient is an important parameter for the decision support of urban stormwater management. However, factors like comprehensive land-use type, variable spatial elevation, dynamic rainfall and groundwater elevation, make the direct estimation of runoff coefficient difficult. This paper presented a novel method to estimate the urban runoff coefficient using the inverse method, where observed time-series catchment outfall flow volume was employed as input for the water balance model and runoff coefficients of different catchments were treated as unknown parameters. A developed constrained minimization objective function was combined to solve the model and minimized error between observed and modeled outfall flow is satisfactory for the presenting of a set of runoff coefficients. Estimated runoff coefficients for the urban catchments in Shanghai downtown area demonstrated that practice of low impact design could play an important role in reducing the urban runoff.

Geoprocessing Applied in the Estimate of Infiltration and Surface Runoff in HPP’s Contribution Watershed

The knowledge of the hydrological regime contributes to the prediction of periods of higher or lower water supply as a function of the frequency and volume of rainfall in relation to the pedological, land cover, and land use conditions. This work aims at evaluating the spatio-temporal variability of the infiltration and runoff potential of an area formed by 4 sub-basins tributary to the São Marcos River in Cristalina (GO). The SCS/NRCS-USDA (2004) method was used, using geoprocessing resources, considering soils in dry, semi-humid and humid conditions. The estimates indicate that rainfall with an average of 6.83 mm, in the September-October transition, in the face of soils in the dry condition does not provide surface runoff. Thus, the variability of pedological characteristics associated with the various conditions of coverage and land use indicates that even the areas with lower infiltration potential begin to contribute effectively with their respective channels in the transition from October to November, when rainfall events are more frequent and significant, and the soils are already in conditions of greater humidity.

Hydrological simulation approaches for BMPs and LID practices in highly urbanized area and development of hydrological performance indicator system

Urbanization causes hydrological change and increases stormwater runoff volumes, leading to flooding, erosion, and the degradation of instream ecosystem health. Best management practices （BMPs）, like detention ponds and infiltration trenches, have been widely used to control flood runoff events for the past decade. However, low impact development （LID） options have been proposed as an alternative approach to better mimic the natural flow regime by using decentralized designs to control stormwater runoff at the source, rather than at a centralized location in the watershed. For highly urbanized areas, LID stormwater management practices such as bioretention cells and porous pavements can be used to retrofit existing infrastructure and reduce runoff volumes and peak flows. This paper describes a modeling approach to incorporate these LID practices and the two BMPs of detention ponds and infiltration trenches in an existing hydrological model to estimate the impacts of BMPs and LID practices on the surface runoff. The modeling approach has been used in a parking lot located in Lenexa, Kansas, USA, to predict hydrological performance of BMPs and LID practices. A performance indicator system including the flow duration curve, peak flow frequency exceedance curve, and runoff coefficient have been developed in an attempt to represent impacts of BMPs and LID practices on the entire spectrum of the runoff regime. Results demonstrate that use of these BMPs and LID practices leads to significant stormwater control for small rainfall events and less control for flood events.

Efficiency of soil and water conservation practices in different agro-ecological environments in the Upper Blue Nile Basin of Ethiopia

In developing countries such as Ethiopia, research to develop and promote soil and water conservation practices rarely addressed regional diversity. Using a water-balance approach in this study, we used runoff plots from three sites, each representing a different agro-ecological environment, e.g., high, mid and low in both elevation and rainfall, in the Upper Blue Nile Basin of Ethiopia to examine the runoff response and runoff conservation efficiency of a range of different soil and water conservation measures and their impacts on soil moisture. The plots at each site represented common land use types（cultivated vs. non-agricultural land use types） and slopes（gentle and steep）. Seasonal runoff from control plots in the highlands ranged 214–560 versus 253–475 mm at midlands and 119–200 mm at lowlands. The three soil and water conservation techniques applied in cultivated land increased runoff conservation efficiency by 32% to 51%, depending on the site. At the moist subtropical site in a highland region, soil and water conservation increased soil moisture enough to potentially cause waterlogging, which was absent at the lowrainfall sites. Soil bunds combined with Vetiveria zizanioides grass in cultivated land and short trenches in grassland conserved the most runoff（51% and 55%, respectively）. Runoff responses showed high spatial variation within and between land use types, causing high variation in soil and water conservation efficiency. Our results highlight the need to understand the role of the agro-ecological environment in the success of soil and water conservation measures to control runoff and hydrological dynamics. This understanding will support policy development to promote the adoption of suitable techniques that can be tested at other locations with similar soil, climatic, and topographic conditions.

Regularity of Erosion and Soil Loss Tolerance in Hilly Red-Earth Region of China

The observations from 14-yr long-term investigation on the soil-water losses in the sloping red-earth (slope 8°- 15°) showed that soil-water losses were closely correlated with land slope and vegetative coverage. Runoff rate in sloping red-earth could be reduced doubly by exploitation, while the soil erosion was enhanced doubly during the first two years after exploitation. Subsequently, it tended to be stable. Soil erosion was highly positively correlated with land slope, i. e. soil erosion increased by 120 t km-2 yr-1 with a slope increase of 1°. On the contrary, soil erosion was highly negatively correlated with vegetative coverage, i. e. soil erosion was limited at 200 t km-2 yr-1 below as the vegetative coverage exceeded 60%. Furthermore, soil erosion was highly related with planting patterns, i. e. soil erosion in contour cropping pattern would be one sixth of that in straight cropping. Based on the view of soil nutrient balance and test data, it was first suggested that the soil loss tolerance in Q2 red clay derived red-earth should be lower than 300 t km-2 yr-1.

Effect of storm pattern on soil erosion in damaged rangeland;field rainfall simulation approach

Raindrop size,rainfall intensity and runoff discharge affect the detachment and transportation of soil particles.Among these three factors,the rainfall intensity seems to be more important because it can change other two factors.Storm patterns can be determined by changing the rainfall intensity during the storm.Therefore,the objective of this research is to test the influence of storm pattern on runoff,soil erosion and sediment concentration on a rangeland soil slope under field rainfall simulation.Four storm rainfall intensity patterns were selected for examining the effects of variations in storm event characteristics on soil erosion processes.The selected storm patterns were:I(45,55 and 70 mm h-1);II(45,70 and 55 mm h-1);III:(70,55 and 45 mm h-1);and IV(55,45 and 70 mm h1).The last pattern is a new one instead of the uniform pattern which has been sufficiently studied in previous researches.The experiments were conducted in field plots(in Kojour watershed,Mazandaran Province,Iran)with an area of one square meter and an constant slope gradient of 18%,surrounded by galvanised sheets.Following the nonuniform prioritization of the storm patterns for the studied variables,time to runoff(I>II>IV>III),runoff volume(III>IV>II>I),sediment concentration(IV>III>I>II)and soil erosion(III>IV>II>I)),it can be generally inferred that each pattern has specific effect on soil erosion processes during a storm.The results of the general linear model(GLM)test indicated that the effects of storm pattern on time to runoff,total runoff volume,runoff coefficient and soil erosion were significant at a level of 99%.The Duncan test showed that the storm patterns can be divided into three groups of III,IV;II;I(for time to runoff),I,II;IV,III(for runoff coefficient),and I;II;IV,III(for runoff volume and soil erosion).

The influence of grazing and cultivation on runoff, soil erosion, and soil nutrient export in the central highlands of Ethiopia

Background:Grazing by livestock and cultivation have been considered as two important causes of soil erosion and nutrient export.However,there has been limited evidence that grazing or cultivation matters to soil erosion and nutrient export in Ethiopia.Hence,this study was conducted in the Galesa watershed in Ethiopia to examine the effects of grazing and cultivation on runoff,soil loss,and nutrient export.Daily values of runoff,soil erosion,and nutrient outflow were measured for three consecutive years following standard procedures.Independent t test was performed to check if the means of runoff,soil loss,and nutrient loss from grazing and cultivated lands were significantly different.Moreover,repeated analysis of variance(ANOVA)was used to test if mean values of runoff,soil loss,and nutrient export varied significantly over the study years.Results:Although the average annual runoff depth was 7.8%higher in grazing land(GL),soil erosion was significantly lower(39%)in GL as compared to cultivated land(CL).Similarly,sediment and runoff-associated annual losses of total nitrogen(N),available phosphorus(P),exchangeable potassium(K),and organic carbon(OC)were low in the GL treatments.Lowest losses of total N(9.30 kg ha^(−1) year^(−1)),available P(0.83 kg ha^(−1) year^(−1)),and exchangeable K(1.84 kg ha^(−1) year^(−1))were recorded in GL treatment.Likewise,lowest losses of sediment-associated total N(32.8 kg ha^(−1) year^(−1)),available P(0.39 kg ha^(−1) year^(−1)),exchangeable K(0.23 kg ha^(−1) year^(−1)),and soil organic carbon(630 kg ha^(−1) year^(−1))were recorded from GL over the 3 years of experimentation.Conclusion:Our results indicate that cultivation increased soil erosion as compared to grazing.Although there were significant reductions in soil erosion and nutrient export from grazing lands compared with cultivated lands,the absolute losses were still high.This implies the need for grazing land management using appropriate physical and biological erosion control measures to increase productivity and reduce soil erosion as well as nutrient export.

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.