This is a review of worldwide land degradation problems. Four themes are emphasized: delineating and estimating the magnitude of soil erosion, quantifying erosion and sedimentation impacts on land productivity, establishing quantitative values for erosion-causing parameters, and implementing global and regional soil and water conservation programs. Papers deal with both developing and developed countries and illustrate how erosion control techniques used in developed countries can or cannot be applied in developing countries.

https://gendocs.ru/docs/29/28948/conv_1/file1.pdf

Soil Erosion and Conservation

The physical processes of raindrop impact and water flow on the leaves and branches of selected tropical tree species were examined under laboratory conditions using simulated rainfall. Inclined branches were found to be particularly efficient in detaining impacting water droplets. This efficiency in raindrop detention increases linearly as a function of branch inclination on branches that are initially dry. On branches that have been thoroughly wetted, this increase in raindrop detention with branch inclination is best expressed as a logarithmic function. At branch inclinations of 60" above the horizontal, the quantity of branchflow was found to be > 80 per cent of the total quantity of impacting rainfall, indicating that < 20 per cent was lost to rainsplash. The strong positive relationship between branchflow and branch inclination explains why trees with large projected areas of steeply inclined upthrust branches have significant quantities of intercepted water draining from their branches and trunks under heavy rainfall conditions. This drainage from the woody frame of trees influences surficial processes by generating both stemflow and large throughfall droplets.

Raindrop impact and water flow on the vegetative surfaces of trees and the effects on stemflow and throughfall generation

http://www.rnr.lsu.edu/people/keim/pubs/Keim_etal_RfallSim_AWR06.pdf

Storage of water on vegetation under simulated rainfall of varying intensity

Many soil erosion models require the evaluation of the energy or the momentum of impacting rain drops. While there are already models to simulate rain drop size-distributions from the rainfall intensity, there are no adequate models to simulate the size-distributions of throughfall under vegetation canopies. This paper suggests that throughfall may be divided into clear throughfall which has the same drop size distribution as the rain (and which may be simulated with existing models) and intercepted throughfall which has a quite different distribution and which is dependent neither on the rainfall intensity nor canopy characteristics like leaf size and texture. The results of a laboratory study are presented in which intercepted throughfall was separated from clear throughfall. They show that the size-distribution of the intercepted throughfall may be very simply described. All previous work in which throughfall drop size distributions were measured is reviewed and examined in the light of the laboratory study. With some exceptions, and despite unquantifiable contamination by clear throughfall, the data show a similar pattern, intercepted throughfall can be described as a normal distribution with a mean diameter of between 4.52 and 4.95 mm and a standard deviation of between 0.79 and 1.30 mm.

The size distribution of throughfall drops under vegetation canopies

Evaluating the influence of canopy species and meteorological factors on throughfall drop size distribution

Rain and throughfall drops were sampled during rain events in a New Zealand beech forest and the frequency distributions of drop mass and kinetic energy calculated. The kinetic energy of throughfall under the canopy was always greater than that of rainfall in the open, notwithstanding interception losses. During a typical rain event in which 51 mm fell in 36 h, the total kinetic energy of throughfail was 1.5 times greater than that of rainfall, and the mean amount of sand splashed from sample cups was 3.1 times greater under the canopy than in the open. It appears that where mineral soil is exposed at the surface, by animal trampling or burrowing for example, rates of soil detachment by splash under a forest canopy will probably exceed those in the open.

M. P. Mosley

Papers

The effect of a new zealand beech forest canopy on the kinetic energy of water drops and on surface erosion