Soil erosion is a major issue globally not only because of its serious implications soil health and productivity but also its impacts on downstream water quality and drainage systems. In general terms, soil erosion problem refers to the ex_situ type in which soil particles permanently move out of the original location and settle downstream along the floodways or waterways. However, from the perspective of mountain farmers, who have to put massive efforts to control erosion during intense rainy seasons, it is a tricky question. In a terraced farm, farmers usually apply flood irrigation starting from the upstream one and allow water to flow down to the lower terraces. In the process, soils from the upstream move down and make way out from the areas. They tend to allow the movement within their lands and apply barrier or take precautionary measures at the outlet. I would love to hear diverse views on this practice, which is inherently problematic to maintain soils health because of focus only on ex_situ erosions?
We love to build sand castles along sea shores as children. What do we learn? Sand piles topple, if not for the bully, then it is because of our own little extra trickle of sand we just placed on top of our sand castles. If we have built enough with the same quality of sand we know its futile to go beyond a certain height without artificial reinforcement. Which is what self-organized criticality is (SOC) about. So SOC informs our baseline efforts and highlights the limits of our human efforts without introducing artificial means. Which now needs factoring as part of the equation since we are all the time harping about ecological sustainability. SOC together with the now almost defunct catastrophe theory was once all the rage. Trying to convince the world that microscopic, localized adjustments have disproportionate impact on the macro structure (i.e. chaos theory, complexity science and the recent 2021 Nobel Prize in Physics awarded to climate researchers and forecasters). In-situ erosion leads to ex-situ and systemic collapse.
Article Self-Organized Criticality
https://medium.com/@Bernard_Lew/why-self-regulation-is-rare-4dd0dd1b3946
You might gain a few ideas on agricultural terraces from some of our articles on gully control in Researchgate. Terrace gradient best between 1-2% slope. Need enough terraces to avoid flow from one to another. If water overflows terraces, the potential exists for failure in erosive fill or heavily disturbed soils. Some gullies in the piedmont of SC, were caused by lack of maintenance and overflowing terraces. Rocks were sometimes used in erosion if terraces had to have a flow outlet. Some soils have a tendency to settle or pipe, so need to compact terrace fill to limit, and build terrace sufficiently deep so they don’t overflow. We found that diverting natural channels into terraces was seldom a good practice.
It it would be better to have a piped water dispersal irrigation system with an outlet at each terrace, than flooding and overflow from one terrace to the next. But terraces are typically installed to control runoff and erosion, and not be an irrigation dispersal system, especially without careful management and attention
I wanted to add a comment or generality from the soil scientists I worked with. I was told it took about a hundred years to make an inch of topsoil. Soil erosion can be a serious issue as far as site productivity, and as mentioned downstream water quality and aquatic habitats. On hill and mountain slopes, topsoils may be thin, and erosion potential high. The universal soil loss equation might be a useful tool and can help estimate and present to others the additive to exponential effect of increasing slope on erosion. And agricultural terraces are a useful mitigation measure if properly located, designed and maintained. But as slope increases, the ability to use them decreases. In SC, USA piedmont highly eroded soils and saprolitic gullies, the limit was probably slopes over 25%, and the gradient of the terrace should be constant in the range of 1-2% to avoid aggradation (filling) and degradation (erosion entrenchment). If the terrace fills with sediment, it will overflow and fail as water is forced downhill, and sometimes this can initiate a gully. Gullies can rapidly reduce agricultural use, as cultivation and trafficability becomes difficult, soil loss is severe to extreme, adjacent groundwater may be tapped and drained. Early farmers of the SC piedmont eventually had to abandon the land due to severe erosion. Author Dr. Stanley Trimble described this is one of his books, and there were several other authors who addressed the severe soil erosion. Another early soil scientist author mentioned in at least one of our papers that the agricultural practices in piedmont soils were also reducing hydraulic conductivity as the result of rainfall dislodging fine particles which were filling soil macropores and reducing infiltration.
Some of the early studies at Coweeta Hydrologic experiment station and probably others of the US Forest Service evaluated the effects of mountain logging, conversion to agriculture on fairly steep slopes of maybe 45%. These paired catchment studies may be very informative to your needs to assess effects of mountain farming and the need for effective mitigation. Helping farmers recognize the signs of excessive concentrated flow and erosion and quick mitigation efforts can help reduce severity of effects. Careful keeping of records of ground slope, terrace spacing, gradient and lengths may help to eventually develop guidelines for your conditions.
Soil erosivity (capacity of erosion causing agents like water and wind) is proportional to the slope of the land means in heavy sloped areas, velocity of flowing water will be more thereby more soil Erodivility (suceptibility of soil to be eroded) as huge soil mass will be detached, transported along with flowing water stream followed by deposition in different places in comparison with smooth surface with uniform topography...upper most fertile layer is washed away resulting in deterioration of soil fertility and soil health..soils of such area may be converted to barren lands hence not suitable to grow field crops... Growing of wind breaks by choosing appropriate tree species to bind roots with soil and thus making good aggregation, which will resist detaching and transporting agents to be disintegrated...
use of sprinkler irrigation or some other controlled pipeline methods may be incorporated so as to ensure optimum moisture instead of wild flooding...
Shian-Loong Bernard Lew Your approach of analysis through self-organized criticality (SOC) offers a new perspective on the issue. Some elaboration of SOC framework in resolving issue at micro or in-situ scale vs macro or ex-situ scale would be immensely useful.
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