Investigation of System Design Criteria and the Capital Cost of Varying Design Return Periods for Soil and Water Conservation Structures

2020 ◽  
Vol 36 (4) ◽  
pp. 511-523
Author(s):  
Daniel Otim ◽  
Jeffrey Colin Smithers ◽  
Aidan Senzanje ◽  
Rianto van Antwerpen
Keyword(s):  
Return Period ◽  
Sediment Yield ◽  
Water Conservation ◽  
Capital Cost ◽  
Soil And Water Conservation ◽  
Peak Discharge ◽  
Return Periods ◽  
Rainfall Runoff ◽  
Design Return Periods ◽  
Soil And Water

Highlights Very few sediment yield events contribute to annual sediment yield. Any rainfall, runoff, and peak discharge event has the potential to generate the most extreme sediment yield event. Twenty year return period recommended for design of conservation structures. Abstract . Design of conservation structures includes both hydrologic and hydraulic designs. Hydrologic design involves estimation of design floods which are required for the sizing of the hydraulic structures. The minimum recommended return period for the design of conservation structures is 10 years but due to the projected levels of risk, and the fact that a few large events are likely to be responsible for the majority of the erosion, the 10-year return period currently recommended may be inadequate. This study investigated system design criteria and the capital cost of varying design return periods for soil and water conservation structures in the sugar industry of South Africa. Observed rainfall data and results of runoff, peak discharge and sediment yield simulated using the Agricultural Catchments Research Unit (ACRU) model were utilized in this study. Relationships between extreme events of sediment yield and the rainfall, runoff and peak discharge events associated with them were analyzed and the capital cost of varying design return periods was also investigated. The results showed that only 0.2% of sediment yield events contributed up to 95% of the annual sediment yield simulated in the sugar production areas in South Africa and that any event of rainfall, runoff and peak discharge had the potential to generate an extreme sediment yield event provided the soil surface was not adequately protected. Based on a sustainable soil loss of 5 t ha-1, the 20-year return period was recommended for the design of soil and water conservation structures. Furthermore, the capital cost implication of varying design return periods from the minimum 10-year return period ranged from an increase of 16% to 35% across the sugar industry. Therefore, given that soil erosion is associated with adverse effects on sustainable crop production and also increases in costs of replanting destroyed crops, the 20-year return period is recommended for the design of soil and water conservation structures in the sugar industry in South Africa. Keywords: Capital cost, Design criteria, Erosion, Return perioW, Risk, Soil and water conservation.

scholarly journals Effects of water and soil conservation works on runoff and sediment variation in the areas with high and coarse sediment yield of the middle Yellow River

2018 ◽  
Vol 38 ◽  
pp. 01033
Author(s):  
Wei Ying Sun ◽  
Pan Zhang ◽  
Li Li ◽  
Jiang Nan Chen
Keyword(s):  
Sediment Yield ◽  
Water Conservation ◽  
Human Activities ◽  
Soil Conservation ◽  
Yellow River ◽  
Soil And Water Conservation ◽  
Contribution Rate ◽  
Rainfall Variation ◽  
Runoff Reduction ◽  
Soil And Water

The areas with high and coarse sediment yield of the middle Yellow River is well known for its severe erosion, high sediment yields. Since 1982 when the 8 key soil and water conservation harnessing regions has been built, the ecological environment has been gradually improved and the amount of sediment and runoff entering the Yellow River has been reduced continuously. Some researchers considered that it was owing to the water and soil conservation works (WSCW), while others believed that it was caused by the rainfall variation, but this has not been quantified for the effect respectively. This paper deals with the effects of WSCW on runoff and sediment variation. The study has been carried out in the Sanchuanhe River watershed, where was listed as one of the 8 key soil and water conservation harnessing regions. The results show that the contribution rate of human activities was 80.2% after 1st harnessing stage (1970-1979), 43.0% after 2nd harnessing stage (1980-1989), in 3rd harnessing stage (1990-1996) it reached 98.4%, and was 44.8% after 4th harnessing stage (1997-2006). With regard to the influence on runoff reduction in the watershed, the contribution rate of human activities was 62.5% compared with the natural factors after 1st harnessing stage (1970-1979), 28.4% after 2nd harnessing stage (1980-1989), in 3rd harnessing stage (1990-1996) it reached 69.6%, and was 37.0% after 4th harnessing stage (1997-2006). The results revealed that human activities exerted the largest effects on the sediment reduction and explained 66.6% of the variation in the specific sediment yield. This study suggests that a combination of human activities and rainfall variation effectively reduces runoff and sediment delivery of the Loess Plateau. Generally The runoff reduction and contribution of rainfall variation to runoff reduction in this area were as large as human activities. After many years' harnessing the great benefit have been obtained in water and soil loss control in this watershed.

scholarly journals Causes of Variations in Sediment Yield in the Jinghe River Basin, China

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Jinliang Zhang ◽  
Yizi Shang ◽  
Jinyong Liu ◽  
Jian Fu ◽  
Shitao Wei ◽  
...  
Keyword(s):  
River Basin ◽  
Sediment Yield ◽  
Water Conservation ◽  
Yellow River ◽  
Soil And Water Conservation ◽  
Water Diversion ◽  
Sediment Discharge ◽  
Jinghe River Basin ◽  
Jinghe River ◽  
Soil And Water

Abstract The Jinghe River remains the major sediment source of the Yellow River in China; however, sediment discharge in the Jinghe River has reduced significantly since the 1950s. The objective of this study is to identify the causes of sediment yield variations in the Jinghe River Basin based on soil and water conservation methods and rainfall analyses. The results revealed that soil and water conservation projects were responsible for half of the total sediment reduction; sediment retention due to reservoirs and water diversion projects was responsible for 1.3% of the total reduction. Moreover, the Jinghe River Basin has negligible opportunity to improve its vegetation cover (currently 55% of the basin is covered with lawns and trees), and silt-arrester dams play a smaller role in reducing sediment significantly before they are entirely full. Therefore, new large-scale sediment trapping projects must be implemented across the Jinghe River Basin, where heavy rainfall events are likely to substantially increase in the future, leading to higher sediment discharge.

scholarly journals Assessing the impacts of different land uses and soil and water conservation interventions on runoff and sediment yield at different scales in the central highlands of Ethiopia

2020 ◽  
pp. 1-15 ◽  
Author(s):  
Tesfaye Yaekob ◽  
Lulseged Tamene ◽  
Solomon G. Gebrehiwot ◽  
Solomon S. Demissie ◽  
Zenebe Adimassu ◽  
...  
Keyword(s):  
Soil Erosion ◽  
Sediment Yield ◽  
Water Conservation ◽  
Moisture Stress ◽  
Quantitative Information ◽  
Soil And Water Conservation ◽  
Land Uses ◽  
Central Highlands ◽  
The Government ◽  
Soil And Water

Abstract To tackle the problem of soil erosion and moisture stress, the government of Ethiopia introduced a yearly mass campaign where communities get together and implement various soil and water conservation (SWC) and water harvesting (WH) practices. Although the interventions are believed to have reduced soil erosion/sediment yield and enhanced surface and ground water, quantitative information on the impacts of various options at different scales is scarce. The objective of this study was to assess the impacts different land uses, SWC and WH interventions on water and suspended sediment yield (SSY) at plot and watershed scales in the central highlands of Ethiopia. Standard erosion plot experiments and hydrological stations were used to monitor the daily water and SSY during 2014 to 2017. The results show differences between treatments both at plot and watershed scales. Runoff and soil loss were reduced by an average 27 and 37%, respectively due to SWC practices at the plot level. Overall, SWC practices implemented at the watershed level reduced sediment yield by about 74% (in the year 2014), although the magnitude of sediment reduction due to the SWC interventions reduced over time. At both scales it was observed that as the number of years since SWC measures have been in place increased, their effectiveness declined due to the lack of maintenance. This study also revealed that extrapolating of plot data to watershed scale causes over or under estimation of net erosion.

scholarly journals Application of a modified distributed-dynamic erosion and sediment yield model in a typical watershed of hilly and gully region, Chinese Loess Plateau

2016 ◽  
Author(s):  
Lei Wu ◽  
Xia Liu ◽  
Xiaoyi Ma
Keyword(s):  
Soil Erosion ◽  
Loess Plateau ◽  
Sediment Yield ◽  
Water Conservation ◽  
Soil And Water Conservation ◽  
Chinese Loess Plateau ◽  
Rainfall Erosivity ◽  
Chinese Loess ◽  
Before And After ◽  
Soil And Water

Abstract. Soil erosion not only results in the destruction of land resources and the decline of soil fertility, but also makes river channel sedimentation. In order to explore spatiotemporal evolution of erosion and sediment yield before and after returning farmland in a typical watershed of hilly and gully region, Chinese Loess Plateau, a distributed, dynamic model of sediment yield based on the Chinese Soil Loss equation (CSLE) was established and modified to assess effects of hydrological factors and human activities on soil erosion and sediment yield from 1995 to 2013. Results indicate that: 1) the modified model has characteristics of simple algorithm, high accuracy, wide practicability and easy expansion, and can be applied to forecast erosion and sediment yield of the hilly and gully region, Chinese Loess Plateau; 2) soil erosion gradations are closely related to spatial distributions of rainfall erosivity and land use patterns, the current soil and water conservation projects are not very ideal for high rainfall intensity; 3) the average sediment transport modulus before and after model modification in recent 5 years (in addition to 2013) is 4574.62 Mg/km2 and 1696.1 Mg/km2 respectively, it has decreased by about 35.4 % and 78.2 % compared with the early governance (1995–1998). However, in July 2013 the once-in-a-century storm is the most important factor causing the emergence of maximum value. Results may provide effective and scientific basis for soil and water conservation and ecological management of the hilly and gully region, Chinese Loess Plateau.

Modelling the effect of soil and water conservation on discharge and sediment yield in the upper Blue Nile basin, Ethiopia

2016 ◽  
Vol 73 ◽  
pp. 89-101 ◽  
Author(s):  
Tatenda Lemann ◽  
Gete Zeleke ◽  
Caroline Amsler ◽  
Luciano Giovanoli ◽  
Hannes Suter ◽  
...  
Keyword(s):  
Sediment Yield ◽  
Water Conservation ◽  
Soil And Water Conservation ◽  
Nile Basin ◽  
Blue Nile ◽  
Blue Nile Basin ◽  
Soil And Water ◽  
Upper Blue Nile Basin

scholarly journals Climate change, vegetation restoration and engineering as a 1:2:1 explanation for reduction of suspended sediment in southwest China

2013 ◽  
Vol 10 (10) ◽  
pp. 12417-12451 ◽  
Author(s):  
X. Ma ◽  
X. Lu ◽  
M. van Noordwijk ◽  
J. Xu ◽  
J. Li
Keyword(s):  
Climate Change ◽  
Land Use ◽  
Land Cover ◽  
Suspended Sediment ◽  
Land Cover Change ◽  
Sediment Yield ◽  
Water Conservation ◽  
River Channel ◽  
Soil And Water Conservation ◽  
Soil And Water

Abstract. Suspended sediment transport in rivers is controlled by terrain, climate and human activities. These variables affect hillslope and riverbank erosion at the source, transport velocities and sedimentation opportunities in the river channel, and entrapment in reservoirs. The relative importance of those factors varies with context but correct attribution is important for policy debates. We analyzed data from the Kejie watershed in the upper Salween, where a combination of land cover change (reforestation, soil and water conservation measures) and river channel engineering (sand mining and check dam construction) interact with a changing climate. Long-term records (1971–2010) of river flow and suspended sediment loads were combined with five land use maps from 1974, 1991, 2001, 2006 and 2009. Average annual sediment yield decreased from 13.7 t ha−1 yr−1 to 8.3 t ha−1 yr−1 between the 1971–1985 and 1986–2010. A distributed hydrological model (Soil and Water Assessment Tools, SWAT) was set up to simulate the sediment sourcing and transport process. By recombining land use and climate data for the two periods in model scenarios, the contribution of these two factors could be assessed with engineering effects derived from residual measured minus modeled transport. Overall 46% of the decrease was due to from land use and land cover change, 25% to climate change to a milder rainfall regime, 25% to engineering measures, and 4% to simulation bias. Mean annual suspended sediment yield decreased exponentially with the increase of forest cover. We discuss the implications for future soil and water conservation initiatives in China.

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