RISCURI ŞI CATASTROFE, NR. XIV, VOL. 17, NR.2/2015

83

CHARACTERISTICS OF FLOW IN THE LOWER CATCHMENT

OF THE ARGEȘ RIVER

MARIANA SOARE

ABSTRACT:- The present paper investigates the flood potential of the lower catchment area of the Arges river. In order to establish the high floods characteristics the maximum monthly and yearly flow series were used, measured at 19 hydrometric stations with observation periods between 10 and 56 years. This paper shows the flood occurrence potential on a monthly and annual scale, important floods being the ones whose flow is higher than defense level (attention level equivalent flow, flood level equivalent flow, danger level equivalent flow). The characteristic elements of the high floods were investigated in order to understand the mechanisms that generate them and to prevent and mitigate the effects resulted. Key words: high floods, the lower catchment of the Argeș river, attention level equivalent flow, flood level equivalent flow, danger level equivalent flow.

1. INTRODUCTION

High floods and flooding represent the most dynamic and dangerous hydric risk events (Romanescu G quoted by Pandi G., 2010). These events are part of the natural conditions of the drainage of rivers and occurrence probability is characterized by the existence of a periodicity. Analysis of flood prevention is important from both the scientific point of view and mostly practical (flood defenses; water management - storage water reservoirs operating; in hydrological forecast) (Pandi G., 2010). In this article the research area is the lower catchment basin of the Argeș River. This area was defined depending mainly on geomorphological criteria. Thus, this area coresponds, most of it, to plain area. The considered limit separates the hill area (Cotmeana Piedmont, Cândești Piedmont and Prahova Subcarpathians – Ciutei leap) from the plain area (Pitești Piemontan Plain, Argeș River Meadow și Târgoviște Plain) afferent to catchment area of Arges River. The analyzed territory sums 12627,6 km

2, meaning 60,99% from the catchment area of Argeș River.

2.DATA BASE AND METHODS

In order to establish the high floods characteristics from the lower catchment

area of Arges River the maximum monthly and yearly flow series were used,

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measured at 19 hydrometric stations within the studied area, with observation

periods between 10 and 56 years (fig. 1 and table 1).

Figure. 1. Stream gauging stations network in the lower catchment area of Argeș river

Table 1. Data on the stream gauging stations in the lower catchment area of Argeș river*

Crt.

no. Stream Gauging station

L

(Km)

F

(Km2)

Hmed

( m )

Study period

1 Argeş Căteasca 169 3550 820 1977-2005

2 Argeş Malu Spart 210 3799 751 1954-2005

3 Argeş Grădinari 220 3830 746 1987-2005

4 Argeş Budeşti 297 9328 389 1950-2005

5 Neajlov Moara din Groapă 23 165 458 1961-2005

6 Neajlov Vadu Lat 66 392 217 1965-2005

7 Neajlov Călugăreni 96 1297 183 1953-2005

8 Dâmbovnic Slobozia 130 3436 130 1964-2005

9 Glavacioc Crovu 48 319 227 1961-2005

10 Colentina Colacu 84 670 127 1957-2005

11 Dâmboviţa Râncăciov 120 883 231 1988-2005

12 Dâmboviţa Dragomireşti 170 1144 191 1969-2005

13 Dâmboviţa Budeşti (Plătăreşti) 37 194 348 1961-2005

14 Dâmboviţa Conţeşti - Lunguleţu 45 123 96 1965-2005

15 Sabar Poienari 93 930 1014 1960-2005

16 Sabar Vidra 185 1105 894 1958-2005

17 Cârcinov Priboieni 204 1391 690 1981-2005

18 Potop Gura Foii 286 2824 399 1966-2005

19 Ciorogârla Bragadiru 24 35.0 162 1976-2005

*According to N.I.H.W.M.

L – Stream length (from its origin to the gauging station); Hmed – Catchment area’s mean elevation (upstream the

gauging station); F - Catchment area’s (upstream the gauging station).

CHARACTERISTICS OF FLOW IN THE LOWER CATCHMENT OF THE ARGEȘ RIVER

85

The following methods were used for characterizing of the maximum discharge

Clasical statistical – mathematical methods for data series processing into their statistical parameters

CAVIS software created by the National Institute of Hydrology and Water Management (N.I.H.W.M.) used for determination of flood waves characteristic elements and flood hydrograph drawing.

3.RESULTS AND DISCUSSIONS

3.1.High-floods genesis A flood is a complex process which is generated by both genetic factors and influencing factors. Genetic factors are represented mainly by climatic conditions that trigger floods (liquid rainfall and/or solid rainfall) as well as some anthropogenic and natural dams breaking. Influencing factors are either natural (geological, morphological and morphometric, pedological, morphometric characteristics of the catchment basin) or anthropogenic (deforestation, improper management of hydrotechnical works, irrational use of lands, etc.). In order to identify the most damaging high floods genesis of the lower basin of the river Argeş, there were studied the first five floods within each gauging stations. From statistical analysis of 96 prior events, with regard to the distribution of high floods during the year, the result was that most were recorded in summer (44,8%) and autumn (24%), followed closely by the spring (21,9%), while in the winter season only 9,4% of all analyzed floods occurred. The months in which there have been most floods are July (21,9%) and June (15,6%) (table 2).

Table 2. The monthly distribution of the largest floods in the lower catchment of the Argeş River

Months I II III IV V VI VII VIII IX X XI XII

Number of high floods

7 2 11 2 8 15 21 7 11 12 0 0

% out of total number of the analyzed high

floods

7.3 2.1 11.5 2.1 8.3 15.6 21.9 7.3 11.5 12.5 0.0 0.0

This monthly and seasonal distribution of the floods shows that they are actually produced mostly due to the quantities of precipitation fell at the river catchment basin level. The presence of major floods including during winter time is likely caused by early melting of the snow combined with high amounts of liquid precipitation as a result of weather factors specific to the plain area. For the rivers that are characterized by the presence of hydrotechnical works, floods are not generated only by natural causes but they are rather influenced by the poor management of the storage reservoirs.

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3.2.The frequency of high floods In order to determine the high flood occurrence probability in the lower catchment basin of the Argeş river , there were regarded as significant high floods those whose flow rates have exceeded the maximum of the corresponding alert stages, namely: QA- the attention level equivalent flow, QI- the flood level equivalent flow and QP- the danger level equivalent flow. The flow rates for the three alert thresholds are based on the values recorded during year 2007. The occurrence frequency of high-floods with maximum flow rates that exceeded the capacities corresponding to those three thresholds of defense were determined on the basis of the maximum monthly flow rates series (table 3). According to the table previously mentioned it can be concluded that the highest frequency of occurrence of high floods shall be recorded on the Neajlov River at the Moara din Groapă hydrometric station, as the maximum monthly flow rate went higher than the equivalent of the attention level and this occurred 296 times within the examined time range, respectively 153 cases of flood level and 78 cases for danger level. Significant occurrence frequencies of high floods have also been identified on the Sabar river at Poenari hydrometric station (70 cases for attention level, 61 cases of flood level and 20 cases of danger level) and to hydrometric Potop river station at Gura Foii hydrometric station (97 cases of attention level, 62 cases of flood level and 14 cases of danger level). Within the analyzed area, there have been identified the years during which there have occurred high floods whose flows exceeded the corresponding thresholds maximum quotas. The highest frequency is represented by the maximum flow rates equivalent to defense flow rates, followed by those of flood, while the maximum flow rates corresponding to danger level are of lowest frequency. The most significant of the maximum flow rates higher than those of equivalent hazard flow rates have been recorded on the Neajlov river Moara din Groapă hydrometric station (6 cases within1969 - January, February, March, April, June, July; 1970 - January, February, March, April, May, July; 2005 - February, March, July, August, September, October; on the Neajlov river at Vadu Lat hydrometric station (5 cases in 2005 in January, February, March, April, July) and on Sabar River at Poenari hydrometric station (5 cases in 1970 during the following months: January, February, March, April, July). In order to highlight the annual frequency of occurrence of major high floods there has been graphically plotted the annual number of floods with flows superior to the equivalent alert stages (fig. 2). From the analysis of the graph there has been noted that on the Argeș River at hydrometric station Budești, in 1970 there have been five high floods with flows superior to equivalent flow attention stage, and in 1955 there were recorded 4 high floods, and in 1953, 1954, 1957, 1973, 1979, 1981 and 2005 three high floods exceeding that threshold. During years 1953, 1954, 1955 and 2005 there have been 3 high floods and each of the mentioned years

CHARACTERISTICS OF FLOW IN THE LOWER CATCHMENT OF THE ARGEȘ RIVER

87

presented higher flow rates than the one equivalent to the attention stage, meanwhile during 1953, 1973 and 1979 two high floods have been recorded with flow rates which exceeded the equivalent for danger stage

Table 3. The frequency of occurrence of monthly maximum monthly flows higher than

equivalent of the attention level (Qa), flood level (Qi) and danger level (Qp) in the lower

basin of the Argeş River*

Crt.

no. Stream Gauging station

Study

period

Number of cases / (%)

>Qa >Qi >Qp

nr.caz % nr.caz % nr.caz %

1 Argeş Căteasca 1977-2005 8 2.30 1 0.29 1 0.29

2 Argeş Malu Spart 1954-2005 55 8.81 40 6.41 16 2.56

3 Argeş Budeşti 1950-2005 59 8.78 40 5.95 18 2.68

4 Neajlov Moara din Groapă 1952; 1961-2005 296 53.62 153 27.72 78 14.13

5 Neajlov Vadu Lat 1965-2005 57 11.59 40 8.13 21 4.27

6 Neajlov Călugăreni 1953-2005 83 13.05 53 8.33 13 2.04

7 Dâmbovnic Slobozia 1950-1952;1962

1964-2005 25 4.53 6 1.09 0 0.00

8 Glavacioc Crovu 1961-2005 35 6.48 10 1.85 4 0.74

9 Colentina Colacu 1952-1953;

1957-2005 60 9.80 23 3.76 4 0.65

10 Dâmboviţa Dragomireşti 1969-2005 30 6.76 2 0.45 0 0.00

11 Dâmboviţa Lunguleţu 1988-2005 61 28.24 31 14.35 15 6.94

12 Sabar Poienari 1960-2005 70 12.68 61 11.05 20 3.62

13 Sabar Vidra 1958-2005 36 6.25 21 3.65 4 0.69

14 Cârcinov Priboieni 1981-2005 23 7.67 2 0.67 0 0.00

15 Potop Gura Foii 1954-1964

1966-2005 97 15.85 62 10.13 14 2.29

16 Ciorogârla Bragadiru 1976-2005 26 7.22 9 2.50 4 1.11

Values determined on the basis of data provided by N.I.H.W.M.

. Figure. 2. The annual frequency of occurrence of the maximum river flows – number of

cases exceeding the warning flow rate (CA), flood flow rate (CI) and danger flow rate (CP)

along the river of Argeș at Budeşti hydrometric station.

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As for the potential monthly high flood in the area, it is noted that floods

with flows superior to the one corresponding to the flood level is recorded most

often in the spring and summer months (table 4) and their genesis are mostly

caused by rainfall. Significant debits are recorded during winter as on Neajlov,

Colentina, Sabar and Ciorogârla rivers (fig. 3).

On the Argeș river, the most frequent high floods with flows exceeding the

level corresponding to the flood level were recorded in May, followed by the

months of June and July (fig. 3).

Table 4. Monthly frequency of occurrence of the maximum flows (in number of cases) in

the lower basin of the Argeş River *

Crt.

no. Stream

Gauging

station

Study

period

Number of high floods Qmax>Qi

I II III IV V VI VII VIII IX X XI XII

1 Argeş Căteasca 1977 –

2005 0 0 0 0 0 1 0 0 0 0 0 0

2 Argeş Malu Spart 1954 –

2005 5 0 5 3 7 6 7 4 1 1 0 1

3 Argeş Budeşti 1950 –

2005 2 1 6 5 10 4 5 3 1 2 0 1

4 Neajlov Moara din

Groapă

1961 –

2005 14 23 19 18 15 17 15 6 4 4 8 10

5 Neajlov Vadu Lat 1965 –

2005 3 10 8 4 1 6 5 0 1 1 0 1

6 Neajlov Călugăreni 1953 –

2005 4 11 14 9 1 4 4 1 1 2 1 1

7 Dâmbovnic Slobozia 1964 – 2005

1 0 0 1 0 0 1 0 1 1 1 0

8 Glavacioc Crovu 1961 –

2005 0 0 4 1 0 1 2 0 1 1 0 0

9 Colentina Colacu 1957 – 2005

3 2 4 2 2 3 2 1 1 1 1 1

10 Dâmboviţa Dragomireşti 1969 –

2005 0 0 0 0 0 0 0 0 1 1 0 0

11 Dâmboviţa Lunguleţu 1965 – 2005

2 1 1 0 4 7 9 4 1 1 1 0

12 Sabar Poienari 1960 –

2005 3 7 11 12 6 7 5 1 3 1 2 3

13 Sabar Vidra 1958 – 2005

3 1 1 1 4 2 5 2 1 1 0 0

14 Cârcinov Priboieni 1981 –

2005 0 0 1 0 0 0 1 0 0 0 0 0

15 Potop Gura Foii 1966 – 2005

3 4 7 15 6 11 8 3 2 1 0 2

*Values determined on the basis of data provided by N.I.H.W.M.

Q max –maximum flow, Qi – flow equivalent to the flood stage value.

CHARACTERISTICS OF FLOW IN THE LOWER CATCHMENT OF THE ARGEȘ RIVER

89

Figure. 3. The monthly frequency of occurrence of the maximum flows higher than the

corresponding flood stage (number of cases) at various stations in the lower catchment of

the Argeș river.

3.3.Characteristic elements of the high-flood waves

Knowing the characteristic elements of the high-flood waves have a practical

importance for understanding the mechanisms of their occurrence in order to

reduce the destructive effects associated (I.Pişota and L. Zaharia, 2002).

Key elements of the high-flood waves are characterized by the following

parameters: the basic flow (Qb); time of growth (Tc); time of decay (Td); total time

(Tt); peak flow (Qmax); volume (W); flood form factor (γ); the layer of water leaked

during high flood (h) (I.Pişota and Liliana Zaharia, 2002).

In order to determine of characteristic elements of the high flood waves and

hydrograph was created within the CAVIS program of the National Institute of

Hydrology and Water Management. They were selected according to the available

data provided by N.I.H.W.M., the biggest high-flood occurred in the lower

reservoir of the Argeş river, calculated characteristic elements of flood waves, after

which it was determined their average value (table 5).

On the Argeş river, the average total time of the high-flood increases from

upstream towards downstream, respectively from 58 hours at Căteasca hydrometric

station, at 144 hours at Budești hydrometric station. A similar situation can be

observed also for the total time of growth, namely from 16 hours at Căteasca to 39

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hours at Budeşti. The form coefficients corresponded to the stations located on the

Argeş river are decreasing upstream to downstream, which meas 0,53 to 0,47 at

Budeşti, having its minimum value of 0,37 at Malu Spart.

On the river tributaries, the average total time oscillates between 56 hours on

the Colentina River at Colacu and 422 hours on Ciorogârla River at Brgadiru.

Formal coefficient ranges between 0,13 on Potop at Gura Foii and 0,67 on

Dâmboviţa river at Budeşti.

The defining elements of the high flood waves are influenced by

morphometric parameters of the reservoirs and the hydrographic network, as well

as by the lengths and slopes of water courses, surface, altitude and average pitch. In

order to accurately reveal these influences there may be established relationships of

hydrologic synthesis, such as Tc- f(L), Tt- f(L), Tc- f(F), Tt- f(F), h – f(F) where Tc

- growth time, Tt - total time, L - length of the watercourse (spring-hydrometric

station), F - surfaces of the hydrographic reservoir (corresponding to the

hydrometric station).

Table 5. Average feature elements of singular flood waves in the lower catchment of the

Argeş river

Stream

Gauging

station

L

(Km) F (Km2)

Tt

(ore)

Tc

(ore) h (mm) γ

W

(mil. m3)

Argeş Căteasca 169 3550 58 16 14 0,53 49

Argeş Malu Spart 210 3799 99 31 40 0,37 151

Argeş Budeşti 297 9328 144 39 33 0,47 313

Neajlov Moara din

Groapă 66 392 139 36 36 0,23 14

Neajlov Vadu Lat 96 1297 134 38 27 0,37 36

Neajlov Călugareni 130 3436 278 64 27 0,35 93

Dâmbovnic Slobozia 48 319 113 30 47 0,24 15

Glavacioc Crovu 84 670 164 85 26 0,38 17

Colentina Colacu 24 35 56 17 94 0,37 3

Dâmboviţa Budeşti 286 2824 59 26 9 0,67 26

Sabar Poenari 120 883 270 46 52 0,19 46

Sabar Vidra 170 1144 105 36 49 0,43 56 Potop Gura Foii 37 194 120 19 98 0,13 19

Ciorogârla Bragadiru 45 123 422 64 443 0,31 55

L – the watercourse length (spring-hydrometric station); F – hydrographic catchment surface

(corresponding to the hydrometric station); Tt – total time of the flood; Tc – flood’s growth time; h –

sewed water layer; γ – form coefficient of the flood; W – volume of the flood.

Such synthesis relations have been developed for Argeș and Neajlov rivers.

After a close analysis of these rivers’ behavior, one can easily conclude that due to

the length and surface increase of these rivers, total times and growth of the flood

also increase. (fig. 4).

CHARACTERISTICS OF FLOW IN THE LOWER CATCHMENT OF THE ARGEȘ RIVER

91

In order to make the correlation between the layer of water sewed and and

the area of the reception catchment the Neajlov River was taken as an example.

a) Tc- f(L) b) Tt- f(L)

c) Tc- f(F) d) Tt- f(F)

Figure. 4. The correlation between times of increased flood (Tc), total times (Tt) and space

factors (L - length of rivers; F - catchment of reception area) on the rivers Argeș and

Neajlov

The aspect of the correlation curve between the previously mentioned

parameters, reflect the fact that water layer leaked decreases as the reception

catchment increases (fig. 5).

Figure. 5. The correlation between the layer of

water of the average flood (h) and the

reception catchment area (F) on the Neajlov

river

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4.The highest floods from the lower catchment of Argeş river In order to highlight the biggest floods occurred in the lower cachment of the

Argeş river there were selected five such events with the highest maximum flow

rates recorded during observations at each gauging station. The total number of

analyzed floods is 95.

At the level of the lower catchment of Argeş river there occurred the most

serious floods during the following years: 1979, 2005, 1972, 1970, 1984, 1969,

1975, 1997 and 1991. Thus, on Argeş, the highest flood, during which the

maximum flowrate reached 1540 m3/s, occurred between Oct. 4-22, in 1972 (fig.

6). Also on the Argeş river, the Malu Spart gauging station it occurred a specially

serious flood during period 19-27 June 1979, when a maximum maximorum of

1380 m³/s was reached.

Figure. 6. Hydrograph of the flood of 4 - 22 October 1972 on Argeş at Budeşti gauging

station

For Neajlov there can be highlighted the floods occurred during 4 -10th of

July 1970 at Moara din Groapă, reaching a maximum maximorum flow of 188

m3/s and during 25.04 – 04.05 1984 at Călugăreni (Q maximum maximorum 392

m3/s).

On Dâmbovnic river, a maximum maximorum flow of 210 m3/s was

recorded durng the event occurred during 20 – 26th of September 2005. As for the

Colentina river, during the observation period, there was noted the flow during

period 1 – 15th of July 1975, when the peak flow reached 57,9 m3/s.

On Dâmboviţa at Budeşti gauging station, the maximum flow of 200 m3/s

occurred during the flood of 20.09 – 11.10. 2005, and Potop river at Gura Foii

CHARACTERISTICS OF FLOW IN THE LOWER CATCHMENT OF THE ARGEȘ RIVER

93

gauging station, the peak flow value reached 600 m3/s during 21 – 24th of June

1979.

As for Sabar river there can be especially remarked the high floods occurred

during 21.06 – 02.07. 1979 at Poenari (Q maximum maximorum of 600 m3/s) and

during 18.06 – 21.07. 1979 at Vidra (Q maxim maximorum of 515 m3/s).

CONCLUSIONS

The monthly and seasonal distribution of the floods shows that they are

actually produced mostly due to the quantities of precipitation fell at the river

catchment basin level. The presence of major floods including during winter time

is likely caused by early melting of the snow combined with high amounts of liquid

precipitation as a result of weather factors specific to the plain area. For the rivers

that are characterized by the presence of hydrotechnical works, floods are not

generated only by natural causes but they are rather influenced by the poor

management of the storage reservoirs.

Within the analyzed area, there have been identified the years during which

there have occurred high floods whose flows exceeded the corresponding

thresholds maximum quotas. The highest frequency is represented by the

maximum flow rates equivalent to defense flow rates, followed by those of flood,

while the maximum flow rates corresponding to danger level are of lowest

frequency. The most significant of the maximum flow rates higher than those of

equivalent hazard flow rates have been recorded on the Neajlov river Moara din

Groapă hydrometric station, on the Neajlov river at Vadu Lat hydrometric station

and on Sabar River at Poenari hydrometric station.

As for the potential monthly high flood on the Argeș river, the results show

that those are recorded in the interval May – July. For the Argeș tributaries, the

high flood potential shows up by the end of the winter and beginning of spring

(February to May).

At the level of the lower catchment of Argeş river there occurred the most

serious floods during the following years: 1979, 2005, 1972, 1970, 1984, 1969,

1975, 1997 and 1991.

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