1. researched characteristics of precipitation that affect erosion and runoff
ZoranGavrilovic, Milutin Stefanoviic, Mileta Milojević, Nikola Zlatanovic,
INSTITUTE FOR DEVELOPMENT OF WATER RESOURCES “JAROSLAV ČERNI” LTD
DEPARTMENT FOR TORRENT AND EROSION CONTROL
JAROSLAVA ČERNOG 80, BELGRADE, SERBIA
TEL , FAX
9/21/2018

2. Introduction
It is indisputable that excess precipitation is the cause of runoff and floods. There is a large number of hydrologic models in use that are defined by the term „rainfall-runoff“. Although the term is seemingly well defined, hydrologic models and the calculations behind them are complex, and, depending on the target group for which they are designed, contain different sets of data such as:

3. “Ripe”, The first experimental station for erosion and torrent field investigation 1954 year
Electrical Hydrometric measuring unit on “Ripe” stream
Erosion totalizing measuring unit

5. - The tame Ripe stream, (catchment area A=0
-        The tame Ripe stream, (catchment area A=0.6km²) with the oldest experimental station for erosion investigations (1954.).

6. The Ripe Brook, the right tributary of the Topcider River, with a catchment area of 0.59 km² is the oldest experimental watershed in the former Yugoslavia. Operate from Up to date.

7. Basics observed data Average annual precipitation is 678mm
Annual rainy days are between
Average Annual runoff coefficient is 0.341
Annually 3-5 rainstorms hit this small experimental watershed and causes torrent flood waves.

9. Basics observed data Year 2010. Was something unexpected?
Annual precipitation was extremely high 927mm. approximately 150% higher than average.
159 rainy days
No one torrent flood wave was recorded.
Small erosion intensity and sediment transport.
Runoff coefficient was unexpected small
Climate change or something else.
Comprising data some old researching come out.

10. River Vlasina is famous from catastrophic torrent flood from 1988.
At the top there is one reservoir for hydroelectric power plant.
All hydrological calculations are done on the base of precipitation and downstream hydrometric observations.
There wasn’t expected water for lake.
Runoff coefficient was less than 0.15.

13. Part of the professional practice in Serbia had a long standing conviction that rivers with catchment basins larger than 200 km ² are not of torrential character. This belief has led to some serious consequences.
Over the past decades, a number of torrent floods have occured on rivers with catchment areas ranging from 500 to 4000 km ². These floods have shown that there are numerous problems in existing hydrological models and that new solutions are needed.
The first flaw is observed in the field of meteorologic observations of precipitation, based on observations of the daily amount of precipitation, which fulfills the needs of hydrologic models for large river systems.
In Serbia, as well as in other European countries, the criterium used for announcing flood threats is the daily rainfall amount of 30 mm/day. Expressed in average rainfall intensity, this is equal to 1.25 mm/h.

15. At the same time starts erosion investigation on experimental catchments and in laboratory.
Laboratory tests help us to understand important role of rain characteristics in runoff and erosion.
Raindrop size distribution is important for runoff and erosion.

16. The search for the solution is directed towards defining the lower threshold of the phenomenon that triggers torrent floods, i.e. the intensity and duration of heavy precipitation, because this is possible to identify and evaluate during the monitoring of the cloud system.
All observed occurrences of torrent floods have been analyzed, as well as the characteristics of rains that caused them.

17. We found one way to solve this problem
We found one way to solve this problem. Namely, our previous preoccupation was erosion intensity and torrential sediment transport.
Erosion Potential method (EPM) is main resault of this long therm investigation process.
Rain is main generator for sediment production and sediment transport. Our previous investigations help us to find connections between rain intensity and dangerous discharge.

18. EPM values of coefficient of soil resistance to erosion (Y) are result of long term laboratory tests done by Institute for the Development of Water Resources “Jaroslav Cerni”, whish is still only one laboratory in the Region.

21. The samples were subjected to a series of artificial rains with standard levels of intensity.
The series of rain intensities for the milder intensity are mm/min.
The second series of rain intensities were mm/min. Gradation of these series was 0.1 mm/min.
The series of rain intensities for extremely heavy intensity were mm/min. Gradation of these series was 0.5 mm/min.

22. Displacement of soil aggregates by artificial rain- samples from Experimental catchment “Ripe” Table 1
No.
Land type and origin
Culture
Sample volume before treatment cm3
Test date
Duration of artificial rain treatment change in volume in %
Rain intensity data and comments
Start time
Washed/ displaced/ time
25%
50%
75%
100% 1
Brown soil,
Trefoil
99.4
08:15
13:10
15:08
Rain intensity 0.51mm/min.
Samples collected in uncontaminated state. Sample No.1. depth 5cm; No.2. depth 15cm; No.3. depth 25cm. Raindrop size 1.2mm mid-diameter. Air temperature lab.+16oC 2
99.8
14:20
15:28 3
99.1
14:11
16:25
Podsolic Brown soil,
Forest
10:12
12:07
99.6
10:43
12:26
99.5
10:42
12:34
Podsolic forest soil
Acacia wood
09:32
10:58
Rain intensity 1.01 mm/min
Raindrop size 1.2mm mid-diameter. Air temperature lab.+16oC
09:41
09:56
09:39
10:06
Podsolic, solifluction
Degraded soil
99.7
08:45
09:47
10:01
Rain intensity 1.45 mm/min
Raindrop size 4.75mm mid-diameter. Air temperature lab. +16oC
09:15
09:31
09:33
09:59
10:17
10:18
Podsolic Brown soil Oak forest cut for dry leaves
96.4
08:25
08:42
08:58
09:26
09:43
Rain intensity 1.0mm/min
98.5
08:48
08:59
09:51
08:36
08:50
09:28
Degraded Smonitca, Ploughland
Wheat
09:36
09:52
11:17
99.3
09:46
10:56
09:37
09:45
10:23

29. Analyzing the gathered data, we have concluded that runoff depends on a few more factors other than the elementary function of rainfall-infiltration-runoff.
The mentioned function has been satisfactory in the case of low intensity rainfall.
It is well known that low intensity rainfall consists of raindrops of small diameter and low downward velocities. These drops do not have significant impact energy and are mostly capillary bound to the soil.

49. On the other hand, high velocity rainfall is characterized by raindrops of large diameter and high velocities, which have significant impact energy. Every impact of such raindrops causes deterioration of the soil, as well as the creation of turbulent conditions for runoff and infiltration.
There are too menu combinations of different terrain characteristic that the best way is preparation of map.

51. Using this methodology, a map of threshold rainfall intensities can be made that would serve as a basis for meteorological radar centres to know precisely which rainfall amount and intensity is alarming for a specific area.

53. Conclusion
Instead, scattered point data is resolved by choosing a suitable statistical processing method with an unreliably defined dependence curve with just two variables, which is unacceptable because erosion depends on many more variables.
The experience obtained from described experiments indicates that the researching of erosion processes and runoff, which inherently have multifunctional dependency, must be accompanied by an experimental phase. In today’s environment with computerized equipment for data acquisition and processing these tasks are by far easier, more accurate and detailed in comparison to the experiments described above.

55. Nature is very complicated and need following simple relations

56. Additional information:
Thank you!
Additional information: