Patterns of Flow Evolution in the Central Area of the Romanian Plain, Case Study: the Calnistea Catchment (Romania)
Total Page：16
File Type：pdf, Size：1020Kb
Caspian J. Env. Sci. 2011, Vol. 9 No.1 pp. 81~95 ©Copyright by The University of Guilan, Printed in I.R. Iran CJES [Research] Caspian Journal of Environmental Sciences Patterns of flow evolution in the central area of the Romanian Plain, Case study: the Calnistea Catchment (Romania) A. Cocos1, O. Cocos2*, I. Sarbu2 1- Hyperion College, Bucharest, Romania 2- Faculty of Geography, University of Bucharest, Bucharest, Romania * Corresponding author’s E-mail: [email protected] ABSTRACT This paper seeks to emphasize the flow variability in the Calnistea catchment by analyzing the local physiographic factors. The research has shown that the amount of precipitation that falls to the ground is low, the rocks in the region are soft, but highly permeable, gradients are gentle in most of the territory and vegetal cover is sparse and therefore cannot hold important amounts of water. Under the circumstances, the flow is controlled especially by precipitation, gradient and rock permeability, which largely explains the rather low values of the drainage density, as well as the frequency with which the rivers dry up completely. The moisture deficit of the summer season is compensated to a certain extent by the existence of a chain of ponds along the main streams. The situation could further be improved if local authorities will find the necessary financial means in order to excavate artificial channels to bring water from the neighboring catchments. Although the flow values are generally low, under exceptional synoptic conditions the heavy rainfalls can lead to the formation of flash floods that can damage settlements, transportation routes and crops. Consequently, it is necessary to build protection levees in the lowlands and to regulate the stream flow. Keywords: Calnistea catchment, Precipitation, Streams, Flow, Discharge. INTRODUCTION balance of the environment through Despite the progress that has been made reckless actions (massive deforestations, so far in science in general, and in the works that render the ground impervious, forecasting of hydrological risks in dyking and reclamation works, particular, many regions of the world constructions that hinder the streamflow, continue to be confronted with catastrophic and last but not least, the burning of fossil hydrological events, which cause serious fuels, which leads to the intensification of material damage and loss of human life. On the greenhouse effect). the one hand, there are areas that are In order to control these devastating events confronted almost every year with the specialists from all over the world have been unleashed rage of the floods that sweep trying to determine as accurately as possible away human settlements, roads, railways, the relationships between the natural and bridges and power lines. On the other anthropogenic elements of the catchments, hand, vast areas are left without a drop of how they interact with one another and how water, inasmuch as the rivers dry up, and they manage to influence the surface and consequently people have to face different sub-surface flow. Besides, the “design of water problems, such as human migration, control structures, reservoir management, epidemic outbreaks and desertification. economic evaluation of flood protection projects, These undesirable phenomena can land use planning and management, flood sometimes be attributed to natural causes, insurance assessment, all rely on knowledge of as for instance magnetic storms, solar the magnitude and frequency of floods” (Rao & eruptions or El Niño effect. Other times, Srinivas, 2008, p. vii). however, those who must be blamed for are The analysis of flow variability in the the people, because they alter the natural Calnistea catchment is therefore rooted in Online version is available on http://research.guilan.ac.ir/cjes 82 Patterns of flow evolution this general effort. The understanding of of maximum discharges and the drawing of the role of every single factor in the local theoretical recurrence curve are based on water budget and the deciphering of the Log-Pearson type III, which better fits the variation patterns of surface flow will be physiographic realities of Romania. The extremely important for the future processing of all the information has been development of the area. done in a modern manner, by using the computer and the Geographical DATA AND METHODOLOGY Information Systems. In order to understand the conditions of flow formation on this territory we have THE STUDY AREA firstly assessed the physiographic factors The Calnistea catchment lies in the that influence to a higher or lesser extent southern part of Romania, within a major this phenomenon. Thus, the study of physiographic unit that goes by the name of geological features has been accomplished the Romanian Plain (Fig. 1). This rather on the basis of geological maps of scale well populated territory has lately been 1:50000 and the existing stratigraphic confronted with long periods of drought, which on the one hand have made some profiles for this region. To investigate the rivers dry up completely and on the other terrain features we have used topographic hand have brought about a moisture deficit maps of scales 1:25000 and 1:50000, as well in the soil, with negative effects on the local as aerial photographs of scale 1:50000, crops. However, the region also experiences which have been supplemented by our own periods when heavy rainfalls lead to the observations and mappings in the field. As occurrence of flash floods, which play far as the climatic conditions are concerned, havoc on households, roads, railways, these have been analyzed based on the bridges and power lines. Under the statistical datasets provided by the weather circumstances, it is necessary to understand stations within the catchment or lying in its the flow variability at the scale of the entire immediate vicinity. Likewise, we have catchment, not only to be able to prevent turned our attention to vegetation and soils, the risk situations, but also to find the most using for their analysis thematic maps of efficient means to respond when such scale 1:100000, whose information has been unwanted phenomena occur. updated by our own investigations in the From the geological point of view, it is field. After getting a comprehensive picture important to note that almost the entire of the runoff controls, we have proceeded region is capped by loessoid deposits of to an analysis of flow variability based on variable thickness. South of the Calnistea the datasets provided by the National axis, these belong to Middle Pleistocene, Institute of Hydrology and Water whereas to the south they are newer, Management, taking seriously into account belonging to Upper Pleistocene. The floodplains and terraces are carved in Mallows ideas and his definition of Holocene formations, represented by statistical thinking (Mallows, 1998). In the loessoid deposits and coarse sediments case of maximum flow, a series of (Ionesi, 1994). What is really important theoretical estimations regarding the about these formations is their high maximum discharges with various permeability, which favors the rapid probabilities of occurrence of the rivers in percolation of meteoric waters into the the Calnistea catchment have been done. ground, thus hindering the runoff. The values have later been employed for As far as topography is concerned, it is the computation of the thickness of water apparent that altitudes are very low. Thus, layer that flows over the entire catchment, the highest elevation (204 m) is in the or some sections of it, as well as for the extreme northwest of the catchment, assessment of total water volume specific exactly on the divide, whereas the lowest for the respective floods. We should note elevation (46 m) corresponds to the that the empirical discharge recurrence confluence of the Neajlov. The largest interval has been computed with the hypsometric step is that of 50 – 100 m, Weibull formula, whereas the computation which accounts for 65% of the whole area. Cocos et al., 83 Fig 1. The geographical location of the Calnistea catchment within Romania Second comes the step of 100 – 150 m, lie at the base of the slopes and terrace which has a share of 28.7%, followed by the scarps. The higher inclination of land steps of 150 – 200 m, below 50 m and above makes gullying processes extremely active. 200 m, which hold together 6.3% of the But the highest grades are found on the area. Another important morphometric river slopes. Although they totalize only element is the gradient. At the scale of the 0.3% of the area, they manage to break the entire catchment, its value is extremely low, monotony of the plain landscape. Here and of only 0009’, which is a typical value for a there, however, the gradients may reach 40 plain region. However, locally one can – 500, as it happens on the northern scarp of notice some higher gradients, which the Burnas Plain and especially at the highlight the slopes of the valleys that scar junction of the Calnistea and Neajlov rivers. the territory. The most extensive are the Surfaces with such gradients are also found quasi-horizontal surfaces with grades along the Glavacioc and the Milcovat, as ranging from 0 to 30. These account for well as on both sides of the younger valleys 88.6% of the region and correspond to the that cross the Burnas Plain. The economic flat interfluves, terraces and floodplains. exploitation of these lands is somewhat On such areas, the water from rain or hindered by gullying and denudation melting snow easily sinks into the ground processes, as well as by superficial or is quickly lost through landslides (Cocos & Cocos, 2007). evapotranspiration and consequently The mean annual temperature specific for sheetflow and gully erosion are almost the Calnistea catchment is 10.40C. The absent. The surfaces that dip 3 – 50 have a graphs drawn on the basis of the datasets share of 7.6%.