Szabó, Szilárd 2005. Analysis of the runoff and its relations to the landscape factors of a small cacthment in
Hungary, In: Kallabova, E. - Vaishar, A. - Zapletalova, J. eds. Geography in Europe of Regions, 6th Moravian
Geographical Conference CONGEO’05 – Luhacovice, Czech Republic, pp. 123-128.
ANALYSIS OF THE RUNOFF AND ITS RELATION TO THE LANDSCAPE
FACTORS OF A SMALL CATCHMENT IN HUNGARY
Szilárd Szabó
ABSRTACT
In this paper in the frame of a landscape evaluation study an erosion sensitivity
examination of a small catchment area is presented. The case is interesting because in our
daily routine often rise problems where our opportunities are restricted due to the few
hydro meteorological (precipitation, evaporation) data. On the base of the results we
marked areas, which are threatened by the erosion of the soil and those where the
accumulation of pesticides and fertilizers used in the agriculture can cause problems.
INTRODUCTION
Key element of the sustainable agriculture is the soil, which is endangered by
several degradation processes: erosion, acidification, compaction, physical and biological
degradation, declining buffer capacity and different pollutions. Erosion and acidification
effect on the largest areas in Hungary (Filep & Blaskó, 1997; Várallyay, 2003). This paper
deals with the soil erosion from the before mentioned two processes.
Damages caused by the erosion are very diverse: there are problems in the areas of
accumulation and the erosion either. On the erosional surfaces the thickness of the topsoil
layer is getting thinner, moreover the most fertile part is removed. There will be less
humus, nutriment and the water management of the soil declines. The transported material
– which is rich in humus in principle – accumulates in the lower surfaces however it often
has low fertility. These are compact soils with scarce pore and the pH is rather acid
(Harrod, 1994; Kerényi, 1991; Szabó, 2003; Thyll, 1997; Rodenburg et al. 2003).
In the frame of this paper a case study of a small foothill catchment area (Fig 1.) is
presented. As a result of our work the erosional and the accumulation fields were identified
in the sample area. The sample area represents well the surrounding environment and
agricultural practice, which makes possible the estimation of the vulnerability of the wider
environs on the base of the results of the study as well.
Bükkzsérc
Perpác
Mt.Kerek
Mt. N yomó
Mt.Avas
Mt .\U+00D5rCserépfalu
Noszvaj
Eger
Cserépváralja
Mt.Kököt\U +00F5
Bükk Mountains
Bogács
Szomolya
Tard
0
3000m
Foreland of the Bükk
Fig. 1. Situation of the sample area
Scientific work was supported by the T 042635 OTKA Fellowship
MATERIALS AND METHODS
The digital elevation model (DEM) of the area had been created with the
interpolation of the contour lines of the area. The 40-60 years long precipitation dataset of
ten meteorological stations (Annual Books of Hydrography 1971-1992) in the broad
environment of the study area had been used. From the dataset average precipitations and
1-6 days maxima for the months and years were calculated. The frequency of 1-6 days
maxima were determined by the method of Goda (1966) at probability levels of 5 and 10%.
The runoff was described using the method of Kenessey (Szabó, 1992.), which based on
the slope conditions, the infiltration of the soil and the soil cover provided by the plants.
Multiplying the map layer of the average runoff factor by the layer of the daily maximal
precipitation using IDRISI we get the value of the specific runoff maximum. Where high
values appear there the erosion is more effective (Zsuffa, 1999). We completed a runoff
direction map on the base of the map of the aspect, which derived from the DEM. The rate
of the evaporation was determined using the temperature datasets of 3 meteorological
stations (Eger, Miskolc and Síkfőkút) (Monthly reports - Climatical data 1960-1987). The
available dataset allowed us to determine the rate of the potential evapotranspiration only,
which was determined according to the method of Thonthwaite (Dobosi & Felméry, 1994).
Soil samples were taken (110 profile and 99 surface sample) and pedological
examinations were carried out. After the labor analysis of the samples we prepared the
spatial presentation of the different soil properties. Statistical analysis has been carried out
on the results of the pedological examinations and on the maps (Zar, 1995).
RESULTS
Analysis of precipitation
The extent of the area is small and there are not significant elevations within it and
for this reason there are not significant differences in the amount of precipitation as well
(mean: 602 mm; min: 585; max: 618). We gain similar spatial pattern when examining the
occurrence of precipitation maxima at different levels of probability. With the exception of
November we find that the additional amount of precipitation is caused by the macro relief.
We have examined the temporal distribution of the one day rain maxima as well.
The highest values occurred in June and August. The June maxima is in connection with
the strengthened cyclone activity after the 8th of June, while in August the maxima is due
to the convective showers and thunderstorms caused by the strong heating of the lower
layer of the atmosphere.
Average precipitation and one day maxima were undergone regression analysis as
dependent variables with the application of several independent variables. According to the
result of the analysis in the case of the average precipitation and the relief the value of the
determination coefficient is 0.72 (p<0.05); in the case of the one day maxima and the relief
it is 0.76 (p<0.05), which shows a relatively strong relationship with the elevation.
According to the results of the analysis the correlation coefficient with the height above the
sea level is r=0.868 (p<0.05). We could not find correlation with the aspect and the
steepness of the slopes, which supported our experience gained by visual analysis
Evaluating the runoff
The average value of the runoff is 235 mm what alone tells not much about the
characteristics of the runoff conditions, since the study area shows a mosaic-like picture
from this aspect. The values of the runoff are between 71 and 420 mm/year.
It is remarkable that the value of the runoff reaches its maximum in the northeastern
part of the area (in a plough land), where the slope is not steep but the infiltration capacity
Scientific work was supported by the T 042635 OTKA Fellowship
of the soil is low and wheat, barley sunflower etc. does not play an important role in the
retention and the drainage of the water into the deep layers of the soil. In that part of the
area compacted Cambisols can be found, which have a high clay content.
The spatial pattern of the daily specific runoff is rather similar to that of the annual
mean specific runoff due to the reasons discussed before (see the chapter of “The analysis
of the precipitation”). The values of that factor however are different: it is fluctuating
between 6 and 36 mm and its average is 19 mm. The maxima occur in the same areas like
in the case of the annual mean runoff. These areas are the most endangered ones from the
aspect of the soil erosion processes, since the speed of the water of the intense rains
reaches its maximum due to the steep slopes, the thin plant cover of the surface and the
poor permeability of the soil. If the area is situated on a long slope the speed and amount of
water running downwards increases and soil erosion becomes more effective. In the
northeastern part in the case of the plough lands there the danger of the soil erosion is
lower because of the weaker effect of the slope and the extremely compacted soil. From
the aspect of the linear erosion the most hazardous areas are those, where the path of the
flowing water is crossed by different linear anthropogenic elements (usually earth roads).
The runoff water, which had been flowing areally, is drained along the roads and in the
tracks of the wheels and depending on the size of the catchment area, the steepness and the
length of the slopes it forms erosion rills and ditches of several size.
In the case of the runoff significant correlation has only be found with the annual
mean precipitation, but it must be emphasized that although the relationship is true the
strong correlation is caused partly by the fact that in the calculation of the variable the
precipitation has been taken into consideration as well.
The reason for the fact that there are no correlations between the runoff and the
factors considered in the study partly is that it is a generalized map. The time pattern of the
runoff is not a uniform one: it depends on the duration and amount of the precipitation the
moisture conditions of the soil and the form (snow or rain) of the precipitation. For
instance the effects of a low intensity, long lasting rain are more favorable from the aspect
of soil erosion than those of a sudden intense summer rain. Higher amount of water runs
off on the surface of a saturated soil than on a soil that is dried up to horizon B. In the case
of the snow (see Boros & Borosné, 1988; Hradek, 1989) we cannot predict the year to year
variations of the amount of the snow. The most important factor is the date of the
beginning and the duration of its melting, in connection with that it is doubtful when and in
what amount will the additional amount of water from the melt of the snow appear.
According to the before mentioned paper the half of the annual erosion occur in that
period.
In the case of the annual mean runoff we have found a correlation stronger than 0.5
with several elements. The correlation coefficient with the elevation was 0.65, with the pH
it was 0.56. In the case of the one day runoff we have found stronger correlations with the
elevation (r=0.67).
Analysis of evaporation
Potential evapotranspiration reaches a high value since the study area has an
intermediate climate between the Bükk Mountains and the Great Hungarian Plane,
although its features hardly differ from those of the Great Hungarian Plane. The relatively
dry climate caused by the rain shadow effect of the Bükk Mountains (Kerényi, 1994).
Determining the actual evapotranspiration we could gain a more precise picture of the
conditions of the evaporation, since as it was visible from values of the precipitation there
are not permanent water supplies in the study area. The picture we gained by the
interpolation of the data of the three stations is – not surprisingly – rather homogenous.
Scientific work was supported by the T 042635 OTKA Fellowship
The only thing we can state that the rate of the evaporation shows a slight decrease towards
the northeast from 751 to 730 mm.
The relationship between the evaporation and the pH is strong r=0.741 (p<0.01). It
can be explained by that due to the high rate of evaporation the amount of water that
infiltrates into the soil and decreases its pH is lower.
Analysis of the infiltration
On the base of the available dataset we cannot draw considerable conclusions
because of the reasons mentioned in the chapter “Materials and methods”. We can
establish that where the rate of the runoff is high the rate of the infiltration is low (Fig. 3).
Where the rate of the runoff is lower the rate of the infiltration will be consequently higher.
The rate of the infiltration is the highest on the alluvial plains of the creeks, in the
valleys between the Nyomó and the Őr hills and in the derasional valley between the
Nyomó and the Kerek hills. This is supported by the fact that by the values of the runoff
significant amounts of water flow aerially towards the bottom of the valley, but there are
not any signs of the linear erosion on the bottom of the valley, what means that there does
not remain an efficient amount of water on the surface to cause linear erosion. The water
evaporates and infiltrates into the soil there. Presumably leaching should be the strongest
there and consequently the pH should be the lowest as well. Since the pH is strongly
influenced by other pedologic features there was not a strong relationship between these
two factors. Beside this we should take into consideration that those are not the values of
the actual infiltration because we could not take into account the evaporation, which could
change the spatial pattern.
The infiltration showed negative correlation with most parameters examined here.
The correlation with the elevation is -0.55, what indicates that the higher the given region
is the lower the rate of the infiltration will be. This establishment is true for the study area
since the slopes are steeper in the higher regions, so the thickness of the sediment layers is
lower therefore the infiltration is weaker. This is strengthened by that there are huge areas
on the steep slopes of the Nyomó hill where the forest was cleared two years ago. The
correlation coefficient between the pH and the infiltration is -0.533. The weak relationship
indicates that the higher the rate of the infiltration is the lower the pH will be. This is
supported by several studies (Stefanovits et al. 1999). The pH is affected by several other
factors (i.g. the CaCO3 content), which are in more direct relationship with it. Additionally
we must remember the fact that we dealt with not the actual values of the infiltration.
Fig 2. 1 day precipitation maximum
Fig 3. Infiltration map of the sample area
Scientific work was supported by the T 042635 OTKA Fellowship
with 5% probability in the sample area
(increasing measure in the direction of
the arrow)
DISCUSSION
In the course of our studies often rise problems, where the task is to analyze the
water balance of a given area, but we cannot mark even a sub-catchment area due to the
small size of our study area. The lack of data can be another problem. Due to the small size
of the study area the number of rain and temperature measuring stations of the Hungarian
Meteorological Service that have datasets long enough for the analysis is restricted. For
this reason the spatial pattern is rather homogenous. In spite of this fact we have found
strong correlations between the elements of the water balance, relief and soil properties in
some cases, which clearly shows that the results are not unreal.
The precipitation can cause problems during the year in two periods: in the summer
by the melting of the snow and in the summer by the intense showers and thunderstorms.
The intense summer rains and storms cause the most severe harm in those areas where the
slopes are steep and the plant cover of the soil surface is thin. The area of the closed
gardens on the eastern slope of the Nyomó hill falls into this category. In that area contour
farming, what could prevent soil erosion is impossible, because long and narrow strips of
land were established there in order to provide the same conditions (favorable and
disadvantageous parts of the slope) for each land owner. This situation is against the
optimal land use structure. From the aspect of the protection of the soil the most important
step should be the establishment of soil protecting forest lanes in the inflection zones of the
slopes in the valleys of the creeks. Those areas at present are used usually as plough lands
and for this reason the risk of the erosion is the highest there. These forest lanes should
play the role of biocorridors and ecotopes for the forest-steppe species, which could not
find shelter for the winter or for building their nests in the uniform plough lands because of
the continuous disturbance. Insect-eater birds and birds of prey could play an important
role in the decrease of the amount of pesticides used in the area. Unfortunately the present
practice is the opposite: on the slopes of the Nyomó hill the forest has been cut off
providing favorable conditions for the soil erosion.
On the base of the analysis we have
found that by the order of magnitude we
could mark the territories, where the ratio of
the runoff or the infiltration is high in spite
the fact that due to the lack of data we could
not apply methods that provide accurate
results (Fig. 4.).
The correlation between the pH and
the elements of the water balance equation is
suitable since the water is not the determinant
but an influencing factor in the formation of
the soil properties. On the base of the results
we could mark the areas that are endangered
by the soil erosion, and those, where the
remnants of the pesticides and the fertilizers
can cause problems.
Fig. 4. Intensive infiltration (1) and runoff (2)
In the cultivated areas, where the rate
parts of the sample area
of the runoff is high the remnants of
pesticides and fertilizers can pollute the surface waters, while the infiltration can make the
quality of the groundwater poor. From the aspect of the infiltration of the pollutants the
Scientific work was supported by the T 042635 OTKA Fellowship
most endangered area is the northeastern part of the study area, namely the Kerek hill. On
the other hand in the derasional valley between the Kerek- and the Nyomó hills the
deposition of the material originated from the neighboring slopes and the infiltration of the
pollutants is expected.
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Scientific work was supported by the T 042635 OTKA Fellowship