ON THE CALCULATION OF ON THE CALCULATION OF MAXIMAL OUTLETS OF SMALL MAXIMAL OUTLETS OF SMALL

MOUNTAINOUS RIVERSMOUNTAINOUS RIVERS(in Armenian conditions)(in Armenian conditions)

Boris Mnatcakanyan,Boris Mnatcakanyan,Kamo Aghababyan, Levon ChilingaryanKamo Aghababyan, Levon Chilingaryan

Institute of Water Problems and HydrotechnicsInstitute of Water Problems and HydrotechnicsYerevan, ArmeniaYerevan, Armenia

E-mail: Kaghabab@aua.amE-mail: Kaghabab@aua.am

22

Abstract:Abstract: In mountainous countries with complex physical In mountainous countries with complex physical

geographical conditions, such as the territory of the geographical conditions, such as the territory of the Republic of Armenia, the calculation of the maximal Republic of Armenia, the calculation of the maximal outlets of small rivers has a very important practical outlets of small rivers has a very important practical meaning, since these rivers bring mudflows and cause meaning, since these rivers bring mudflows and cause serious damage to many branches of economy.serious damage to many branches of economy.

The methods used to evaluate the maximal outlets are The methods used to evaluate the maximal outlets are often not accurate enough.often not accurate enough.

We have carried out a comparative research of the We have carried out a comparative research of the case study of the Marmarik river with application of a case study of the Marmarik river with application of a number of methods used in Soviet times and methods number of methods used in Soviet times and methods used abroad. The research shows that when used abroad. The research shows that when calculating the maximal outlets of small rivers it is calculating the maximal outlets of small rivers it is more efficient to use the formulae or the maps, so far more efficient to use the formulae or the maps, so far as the values calculated with the use of these as the values calculated with the use of these formulae and maps are close to the maximal outlets formulae and maps are close to the maximal outlets values defined by the rivers with long values defined by the rivers with long series of series of measurements. measurements.

33

For determination of the maximal flow For determination of the maximal flow parameters at present in Armenia the former parameters at present in Armenia the former Soviet Union norms are used. However these Soviet Union norms are used. However these norms are not used in every complicate physical norms are not used in every complicate physical geographical Armenian conditions, particularly, in geographical Armenian conditions, particularly, in hydrologicaly uninvestigated mountain rivers and hydrologicaly uninvestigated mountain rivers and the acting waterfalls. For the last methodological the acting waterfalls. For the last methodological indications and recommendations, taking into indications and recommendations, taking into account local conditions of floworganizing are account local conditions of floworganizing are used. For the maximal flow calculation it is used. For the maximal flow calculation it is advisable to use regional methods of counting the advisable to use regional methods of counting the flows, which are formed by intensive flows, which are formed by intensive precipitations.precipitations.

These methods take into account identifically These methods take into account identifically different ways physical, geographical, climatic different ways physical, geographical, climatic and other factors, which influence on the and other factors, which influence on the maximal flows formation. maximal flows formation.

44

The working out and using The working out and using methods in Armenian conditions methods in Armenian conditions are:are:

1. 1. The method of determination of regional The method of determination of regional parameters and hydrological indicators of the parameters and hydrological indicators of the maximal flows gives a chance to calculate the maximal flows gives a chance to calculate the middle maximal flow for each region. In result of middle maximal flow for each region. In result of the regressional analysis the corresponding the regressional analysis the corresponding single formula has received by the method`s single formula has received by the method`s author.author.

55

2. The method of mudflow determination 2. The method of mudflow determination installs the connection between installs the connection between morphometrical parameters of the pond, morphometrical parameters of the pond, flood precipitations and regional climatic flood precipitations and regional climatic factors.factors.

For determination of the flood consumtion For determination of the flood consumtion in this method is used the known regional in this method is used the known regional empirical formula. According to this empirical formula. According to this formula the maximal modulus of mudflow formula the maximal modulus of mudflow diminishes with the increase of water diminishes with the increase of water catchment area. The use of this method is catchment area. The use of this method is advisable for the water catchments area advisable for the water catchments area no more than 1000 km2.no more than 1000 km2.

66

33. The method of maximal intensity of flow used . The method of maximal intensity of flow used the connection between maximal flood the connection between maximal flood parameters and rain intensity as well as parameters and rain intensity as well as connections between coefficient of flood and connections between coefficient of flood and relief parameters. The method is recommended relief parameters. The method is recommended for the small water catchments area (less than for the small water catchments area (less than 200 km2), belonging to the pond of the river 200 km2), belonging to the pond of the river Araks. Araks.

44. This method of a flood definition in water . This method of a flood definition in water catchments area more than 200 km2 , seems to catchments area more than 200 km2 , seems to be most simple. The method uses linear be most simple. The method uses linear connections between a freshet rain with 1% flow connections between a freshet rain with 1% flow rate and maximal rate received by an empirical rate and maximal rate received by an empirical way. The coefficients of linear connections are way. The coefficients of linear connections are received as a result of the observed data`s received as a result of the observed data`s statistical analysis.statistical analysis.

77

55. The method applied for water catchments area . The method applied for water catchments area with the up to 50 km2 and belonging to the pond with the up to 50 km2 and belonging to the pond of river Kur establishes a connection between of river Kur establishes a connection between maximal flow and precipitations with the same maximal flow and precipitations with the same provision. The method takes into account provision. The method takes into account morphometric parameters, soil covering and the morphometric parameters, soil covering and the unisual intensity of flood. unisual intensity of flood.

66.The other method applied for the water .The other method applied for the water catchments area more than 300 km2, establishes catchments area more than 300 km2, establishes a connection between maximal consumtion of 5% a connection between maximal consumtion of 5% provision and by the size of the catchments area, provision and by the size of the catchments area, similarly a formula of reduction. Empirical similarly a formula of reduction. Empirical coefficients of the formula are received as a coefficients of the formula are received as a result of statistical analysis.result of statistical analysis.

88

Though the described methods are based on certain Though the described methods are based on certain statistical analysis, they give no reliable results.statistical analysis, they give no reliable results.

The author’s group came to such conclusion after the The author’s group came to such conclusion after the work carried out by the order of World bank, on work carried out by the order of World bank, on recalculation of inflow of 23 large reservoirs in recalculation of inflow of 23 large reservoirs in Armenia.This method using in foreign countries, has Armenia.This method using in foreign countries, has given strongly overestimated results in comparison given strongly overestimated results in comparison with CH uPom. For example, the calculated results for with CH uPom. For example, the calculated results for river Akhurian basin, the largest reservoir of Armenia, river Akhurian basin, the largest reservoir of Armenia, on the methods of PMP is higher than CH u N-y on the methods of PMP is higher than CH u N-y (10400 m3/cek) against (1220 m3/cek).(10400 m3/cek) against (1220 m3/cek).

For an estimation of applicabity the first best For an estimation of applicabity the first best approach has been comparative analysis of the results approach has been comparative analysis of the results of calculations, made on the basis of different of calculations, made on the basis of different normative methods. Of course, such calculations normative methods. Of course, such calculations should be made for small and well investigated river should be made for small and well investigated river ponds, where the applied compared methods are the ponds, where the applied compared methods are the same according to their recommendations. There is a same according to their recommendations. There is a such pond in Armenia and it is river Marmarik, inflow such pond in Armenia and it is river Marmarik, inflow of river Razdan. of river Razdan.

Map-Scheme of Marmarik River BasinMap-Scheme of Marmarik River Basin1- gauge line Marmarik-Hanqavan, 2 – gauge line Marmarik – Aghavnadzor,1- gauge line Marmarik-Hanqavan, 2 – gauge line Marmarik – Aghavnadzor,3 – gauge line Gomur - Meghradzor3 – gauge line Gomur - Meghradzor

1010

Actually, this pond hydrologically is rather well-Actually, this pond hydrologically is rather well-investigated. The area of the pond is not so large, investigated. The area of the pond is not so large, that why the regional method could be applied that why the regional method could be applied here. here.

The consumption and hydrographs of maximal The consumption and hydrographs of maximal flow by P=0.01%, 0.1%, 1%, 5%, 50% provision flow by P=0.01%, 0.1%, 1%, 5%, 50% provision are determined for the calculating river site. For are determined for the calculating river site. For the comparative estimation of the methods, the comparative estimation of the methods, beside the consumtion of Qp, and their statistical beside the consumtion of Qp, and their statistical characteristics (Cv, Cs, RAUT), another important characteristics (Cv, Cs, RAUT), another important parameter (the reduction indicator parameter (the reduction indicator n n of the flow of the flow maximal modulus) choosen. The latter is defined maximal modulus) choosen. The latter is defined by the relation Q2 / Q1 = ( F2 / F1)n, where Q1, by the relation Q2 / Q1 = ( F2 / F1)n, where Q1, Q2 are the quantity of consumtion; F1, F2 are Q2 are the quantity of consumtion; F1, F2 are the areas of reservoir, corresponding with two the areas of reservoir, corresponding with two sequenced calculated sites of river.sequenced calculated sites of river.

1111

Table. Maximal flood parameters of Marmarik riverTable. Maximal flood parameters of Marmarik river

River site and

observed line

parameters

Parameters

Methods

Moments

Likelihoods

Grapho-

analitical

Shower floods

Limit intensity of flood

Marmarik-Hanqavan

1957-1994.

Cv=0.335

Cs=0.771

Q=17.15m3/s

R = -0.15

Q0.001% 70.0 65.9 - -

Q0.01% 55.4 53.5 51.8 147 311

Q0.1% 50.2 43.7 43.6 114 240

Q1% 39.4 34.4 34.6 84.1 178

Cv 0.437 0.34 0.338 - -

Cs 0.768 1.02 1.02 - -

Cv/Cs 1.76 3 3.01 - -

1212

Marmarik-Hanqavan

1942-1987.

Cv=0.45

Cs=1.12

Q=39.95m3/s

R = -0.02

Q0.001% 197 297 - - -

Q0.01% 164 217 182 298 -

Q0.1% 132 162 145 230 -

Q1% 100 105 106 170 -

Cv 0.49 0.47 0.50 - -

Cs 1.11 1.88 1.50 - -

Cv/Cs 2.26 4 3 - -

Index of reduction

degree

P=0.01% 0.764 0.986 0.885 0.498 -

P=0.1% 0.681 0.922 0.846 0.494 -

P=1.0% 0.656 0.786 0.788 0.495 -

1313

The results of the calculations show, that The results of the calculations show, that the quantities of the consumtion with the the quantities of the consumtion with the same provisions, made by regional same provisions, made by regional methods, are considerably more, than the methods, are considerably more, than the results made by normative methods, results made by normative methods, admitted by hydrology. The difference of admitted by hydrology. The difference of the parameters of reduction of flow the parameters of reduction of flow maximal modulus, determined by this maximal modulus, determined by this methods, is also considerable.methods, is also considerable.

This analysis, not detailed essentially, This analysis, not detailed essentially, shows the way of improvement of regional shows the way of improvement of regional methods and its difficulties.methods and its difficulties.

1414

ConclusionsConclusions1.The norms and methods of defining the 1.The norms and methods of defining the

parameters of maximal runoft need to parameters of maximal runoft need to be improved and regulated for their use be improved and regulated for their use under different conditions, scales and under different conditions, scales and certain soluable issues.certain soluable issues.

2.The improvement of the regional 2.The improvement of the regional methods is possible by means of methods is possible by means of application of comparatine analysis with application of comparatine analysis with tested normative methods, which are tested normative methods, which are applied for rivers under study.applied for rivers under study.

3.Alongside the improvement of regional 3.Alongside the improvement of regional methods it is crucial to select the methods it is crucial to select the structure of calculation formulae and structure of calculation formulae and reduction coefficient.reduction coefficient.