MINISTRY OF EDUCATION & TRAINING
UNIVERSITY OF TRANSPORT AND COMMUNICATIONS
Nguyen Anh Tuan
STUDYING THE DETERMINATION OF A NUMBER OF RAIN
PARAMETERS TO MAKE CONTRIBUTIONS TO COMPLETING THE
FORMULA OF DESIGN FLOW OF SMALL SIZED DRAIN WORKS ON
ROAD UNDER THE CLIMATIC CONDITIONS OF VIETNAM
Major: Building auto road and city road Code: 62.58.30.01
SUMMARY OF DOCTOR OF ENGINEERING
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Hanoi-2014
PREAMBLE
1. Background for the research.
Today, the transportation network has been expanding; urban areas, industrial zones have been developed at a rapid pace. We require a formula to calculate the design flow for simple, easy-to-calculate small drainage structures with the acceptable accuracy.
In recent decades, Vietnam has been seriously affected by the climate change phenomenon, increasing the extreme climate phenomena, affecting the rainfall regime in Vietnam. Therefore, it affects the rainfall parameters used in calculating the design flow of drainage works on the road Qp. The use of the research results, previous rainfall data in calculating Qp becomes the reduced reliability, with large errors, giving rise to the damages to works, delaying the transport, increasing costs of repairing and maintaining, affecting the living environment…
This clearly shows the reality out of the practice, such as the phenomenon of damages to small drainage works on the road due to increasing flood; damages can occur immediately or only a few years after being put into use; phenomenon of water storage at the upstream causes flooding to the fields and villages, affecting the agricultural production often occurs in the Central Region after completing the construction of roads; the phenomena of street inundation after the heavy rains in some urban areas of Vietnam makes difficulties, disturbance for activities and production. . . Obviously, there are outstanding problems, emerged problems of determining the rainfall parameters in formula of calculating Qp of small water drainage works on the roads in Vietnam today.
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From the above urgent requirements, the dissertation has been
selected for the research. 2. Research objectives.
- Theoretical research, analysis of nature, proposing principles and methods, formula for determining the parameters of rain used in the formula of calculating design flow of small drainage works on roads under the conditions of Vietnam.
- Applying into the practice: immediately, because there has not been enough conditions, targets of determining specific valuation of parameters on rainfall at 12 typically selected meteorological stations, these values are proposed for reference to the practical use in calculating design flow of drainage works on roads in these areas of Vietnam. 3. Research contents.
- The thesis focuses on researching and resolving rain parameters. This is the decisive, important and indefinite parameters in calculating Qp of small drainage works on the roads, totally depending on the particular characteristics of the climate in Vietnam. The rainfall parameters of the research are as follows:
+) The study shall determine the calculated daily rainfall Hn,p at a design frequency tailored to the characteristics of the weather changes in Vietnam.
T and issues of rain zoning in line with the requirements on calculating design flow of small drainage works on the roads in Vietnam.
+) The study shall identify specific factors of the rain shape Y
+) The study shall determine parameters on the designed rainfall intensity aT,p, corresponding to the concentration time of designed water and design frequency. Calculated rain intensity parameters a T,p is the general impact parameter in calculating design flow of drainage works on the roads.
- The above are the parameters on rain used in the formula of
calculating design flow of drainage works on the roads. 4. Research methods.
Statistical analysis is the main method used in the thesis.
5. Scientific meanings and pratice of the project.
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- Researching characteristics of rainfall changes, contributing to further elucidate the unusual situation of change of rain in the territory of Vietnam in recent decades. Realizing the urgency to recalibrate or gradually replace the new database of rainfall in line with the weather phenomenon under the affects of the climate changes; suggesting solutions to coping with the phenomenon of radical changes in rain in calculating design flow of water drainage works on the roads in Vietnam today.
- The study shall determine the parameters of rainfall (calculated daily rainfall Hn, p, calculated rainfall intensity aT,p, logical rain zoning and other characteristics of rain: Y T, Sp, A, B, m, a ) suitable for the climatic conditions in Vietnam used in the formula Qp calculating the small drainage works on the roads. A few researched rain parameters identified in the thesis (such as daily calculated rainfall parameters H n,p, typical characteristic rain shape coefficient Y T) can also be used in the Sokolopsky formula calculating design flow for medium and large basins; used in calculating showers - flow with NAM - MIKE model with reliable results.
- Rain gauge stations in Vietnam are numerous, but most of them are used to measure daily rainfall and few of them are recording rain gauge stations, so that when the method of directly determining the calculated rain intensity parameters are based on recording rain gauge data, then researching the construction of empirical formula in indirectly calculating the rainfall intensity aT,p in the thesis; issues of transferting the calculated daily rainfall Hn,p into the calculated rainfall of each short time HT,p is necessary for calculating the peak flow of the design flood of the basin of drainage works on roads in Vietnam.
- To better plan the flood prevention, firstly, it is required to logically zone flood, in accordance with rainfall characteristics of each region. The thesis has researched proposals on criteria, rain zoning methods for mapping the logical rain zoning with a large proportion in accordance with the requirements for calculating flood flow of the small basins of small drainage works on the roads in Vietnam.
- The thesis has established the specific parameters of rain, such as calculated daily rainfall Hn,p according to the design frequency, typical coefficienmt of the rain shape Y T , rain strength Sp , factors of the climate
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zones A, B, coefficient of the rain shape m, the regression coefficient of the climate zone α, standard rainfall intensity aTO,p used in 07 empirical formula that the dissertation researches and develops to calculate the rainfall intensity aT,p corresponding to the concentration time of calculated water and design frequency, for 12 selected typical meteorological stations, including stations at Muong Lay Town-Dien Bien Province, Tuyen Quang City, Lang Son City, Lang-Hanoi, Ha Dong-Hanoi, Son Tay Town-Hanoi, Vinh City, Dong Hoi City, Da Nang City, Nha Trang City, Buon Ma Thuat City, Can Tho City, with the actual rainfall records from 1960 - 2010, reference recommendations forn the practical use to compute the design flow of small drainage works on the roads today in these regions of Vietnam. 6. New contributions of the dissertation.
- Determining the values of calculated daily rainfall Hn,p according to the design frequency at 12 selected meteorological stations on the basis of long actual rainfall recording sequence from 1960 to 2010, in which the last time is supposed to correspond to the new context with the impact of climate change phenomena, applied to calculate the design flow of small drainage works on the roads in accordance with current design standards TCVN9845:2013 [5] or using Sokolopsky formula in computing the design flow for medium and large basins (in the regions located with these meteorological stations).
T can also be used as a criterion for zoning the rain. - Summarizing and researching to improve into 7 types of empirical formula in calculating the calculated rain intensity parameter a T,p
- Determining the values of characteristic coefficient of the rain shape Y T for the regions of 12 studied meteorological stations with the rain gauge period from 1960 to 2010, used to calculate the rainfall intensity corresponding to the water concetrating time of the basins and the design frequency used in the standard TCVN9845:2013 [5] to calculate the design flow of small drainage works on the roads. At the same time, it is an important parameter used to calculate the transfer from the calculated daily rainfall Hn,p to the calculated rainfall of each short timeHT,p used in Sokolopsky formula to calculate the design flow for medium and large basins in calculating showers-flow with the NAM- MIKE model with the reliable results. Also, the characteristic rain shape coefficient Y
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corresponding to the water concentration time of the basin and the design frequency used to calculate the design flow of small drainage works on the roads in Vietnam corresponding to the different conditions on rainfall data available in the design areas, in which there are 3 types of new improved formula of the thesis, the formula remains the coefficients in the formula new building for the thesis area 12 meteorological stations selected for the study period rainfall in 1960-2010.
Chapter 1: OVERVIEW ABOUT THE RESEARCH ISSUES
1.1. Domestic and international related researches. 1.1.1. Theoretical basis of the formula for determining the maximum flood current flow due to rain on the catchment [32].
- The formula of the limited intensity determining the design flood peak flow is drawn from the famous flow formula whose basis is the theory of concentrating water from the basin. This theory was firstly analyzed and researched by USSR scientists (N.E. Dongov, M.E. Velikanov and M.M.Protodiakonov) and it is now widely used in the world in the field of hydrological computation. The assumptions are. +) Basins are evenly shaped, the river bed in the middle. +) Rain and losses are evenly distributed over the entire basin and with unchanged intensity during the computation time.
+) Considering the rain frequency of flood flow to be equal to the flood flow frequency.
- By analyzing rules of water running from slopes of the basin to drainage works, the authors of the theory of concentrating water from the basin have drawn the formula for determining the maximum flow of the design flood flow.
=
Q
j aK . .
,t
p
(1.1)
. F p In which: Qp is the design flow at frequency p; F is the catchment area
j is the flow coefficient with regard to the amount of lost
rain water at ,p is calculated rainfall intensity at water concentration time t of the basin and the frequency p. It is the max average
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rainfall intensity during the water concentration time t and frequency p K is the unit conversion coefficient when elements in the formula are not calculated at the same unit. K = 16.67 when Qp is in m3/s, at ,p calculated in mm/ph, F in km2.
- Formula (1.1) is the basic formula. From the basic formula (1.1), very many authors have studied the application and completed to suit the actual conditions in terms of rainfall intensity distribution law, water running conditions on the natural basins. 1.1.2. Formula defining the design flow for small drainage works on the roads in some countries and in Vietnam. 1.1.2.1. In some countries: countries with the developed science such as the U.K., the U.S., Russia, Japan, China, etc use the limited intensity formular in the form (1.1) to determine the design flow Qp for small water drainage works on the roads. 1.1.2.2. The formula for determining the design flow for small drainage works on the roads in Vietnam
- The formula of the limited intensity of the standard TCVN9845:2013: Calculation of flood flow characteristics [5]: applied to the basin with F £
Q
A
.
j .
d .
p
1
p
FH . pn , In which: Ap is the relative flood peak flow module at the frequency p
100 km2. = (1.9)
t / t Hn,p is the calculated daily rainfall at the frequency p d 1 is the factor with regard to effects of ponds, lakes, and
Ap = 16.67Y
swamps.
- Limited intensity formula of National University of Civil Engineering (the formula proposed by Prof., Dr.Nguyen Xuan Truc) [3], [32].
The small drainage structures on roads in Vietnam often have the small catchment area (usually less than 1 km 2 to a few km2), so the water concentration time t is short. Therefore, the calculation of Qp is based on the rain intensity parameters with the short calculation time, but the high rain intensity will be more accurate than using the daily rainfall parameters as in the formula (1.9) of the design standard [5]. With that
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=
viewpoint, since the 1980s, Prof. Dr. Nguyen Xuan Truc has proposed using the following formula (1.10) to calculate the design flow Q p for small drainage structures on roads with the basin area F£ 30 km2 in Vietnam.
Q
j 67.16
df ..
p
a . t F . p ,
1
(1.10)
With: f the flow reduction coefficient depending on the basin area.
=
- Limited intensity formula used in calculating urban road drainage under the design standard TCVN7957:2008 [8].
. qC
Q
,t
p
. F p With: C is the flow coefficient, depending on the nature of the basin
(1.11)
surface and p qt ,p is the rain flow module or rain intensity according to the calculated volume corresponding to the water concentration time t and design frequency p qt ,p = 166.67at ,p In which: qt ,p in liter/s/ha, at ,p in mm/ph.
1.1.2.3. Sokolopsky Formula [3], [15], [32].
(278.0
H
H
)
t
,
p
0
=
+
Q
j .
.
Ff .
d .
p
Q 0
t
l
This is the kind of volume formula used to calculate the flow of water drainage works on the roads with the basin area F>100 km2. - (1.12)
With: Ht ,p is the calculated rain flow at the water concentration flow t of the basin and the frequency p. It is the max rainfall during the water concentration time t and the frequency p (mm) H0 is the initial lost rain water (mm) tl the duration of rise (h) f is the factor of flood shape , d is the coefficient with regard to the influence of reduced flow of ponds, swamps and forests in the basin Q0 the water flow in the river before the flood (m3/s).
1.1.3. The problem of determining the parameters in the formula for calculating the design flow of small drainage works on the roads.
The parameters of rain in the formula for calculating the design flow of small drainage works on the roads are: calculated daily rainfall Hn,p at the design frequency p; characteristic rain shape coefficient Y T and the
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issue of rain zoning; the calculated rain intensity at ,p at the water concentration time t and design frequency p. 1.1.3.1. Calculated daily rainfall Hn,p.
- Calculated daily rainfall Hn,p is determined by the statistical analysis method on the basis of sequence of data measuring actual daily rainfall for many continuous years at rain gauge stations within the project design area.
- Up to now, the fullest database about Hn,p in Vietnam was founded in 1987 in accordance with the design standard TCVN9845:2013 [5], for 589 points of rainfall gauge across the country with the frequency p=1%, 2%, 4%, 10%, 25%, 50%. Since then now, it has passed over 25 years, the rainfall regime in Vietnam has been changed, influenced by the phenomenon of climate change, so the database has become less accurate so far. 1.1.3.2. Characteristic coefficient of the rain shape Y T and rain zoning. - Up to now in Vietnam, there have been some projects on zoning T ~ rain and building the coefficient Y T for each rain zone. The rain partitioning projects are subdivided by the rainfall intensity, i.e. only paying attention to the relation of reducing the rainfall intensity by the calculated interval aT ~ T. Like the rain partition of the year 1977 of the Irrigation Standard QP.TL.C-6-77 [7], it divided the Northern Region into 10 rain zones; the 1980 rain partition of Hoang Minh Tuyen divided the entire territory of Vietnam into 15 rain zones [60]; the 1991 rain partition of Hoang Niem and Do Dinh Khoi divided the whole nation into 18 rain zones. In 1993, Dr. Trinh Nhan Sam also divided the entire territory into 18 rain zones as above, but the coefficient value Y T established in rain zones is a bit different [29], [40]. Results of rain zoning in 1993 were included in the design standard TCVN9845:2010 [5], which are now used to calculate Qp for the drainage works on the roads.
- Therefore, over the annual periods, the rainfall regime of Vietnam has been changed, leading to the fact that the rain zoning is also adjusted accordingly and characteristic rain shape coefficient value shape Y T in the rain zones are also corrected accordingly.
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1.1.3.3. Defining the calculated rain intensity aT,p: with the following instructions.
- Direct calculation aT,p: on the basis of sufficient surbey data available for recording rain gauge at the meteorological stations, using the method of statistical analysis to calculate the calculated rainfall intensity value aT,p in calculated rain period T and the design frequency p. When calculating the flow of drainage works, the calculated rain period T is drawn by including the water concentration time t of the basin.
=
a
. H
, pT
, pn
T T
- Determining the calculated rainfall intensity aT,p based on the calculated daily rainfall Hn,p and characteristic rain shape coefficient Y T Y (1.14)
This method is proposed by Alexayev. It has been used in Vietnam to calculate Qp in the design standard TCVN9845:2013 [5].
- Building the empirical formula to calculate aT, p. The empirical formulas are all built based on the characteristic rain strength S and the rain form factor m to determine the rainfall intensity calculated aT,p. The basic form is: aT,p = Sp / Tm = (A + B.lgN) / Tm.
From this basic formulation, it has been developed into a lot of other empirical formulations to suit the climatic conditions in each country, such as the formula of the U.S., India, Russia, China, Japan, Korea China, Indonesia, Malaysia, etc. In these formulas, compared to above basic formulations, they can be added or subtracted a few regression coefficients.
In Vietnam, there have been many studies to suit the climatic conditions of the nation, typically:
=
a
, pT
lg. NBA m T
./ The research of Prof., Dr. Nguyen Xuan Truc in the year 1980 + for 18 meteorological stations:
=
a
, pT
+ lg. NBA + mk NbT ( . ) ./ The research of Dr.Tran Viet Lien in the year 1979 for 47 +
=
a
, pT
./ The research of Dr.Tran Huu Uyen in the year 1973 for 34 meteorological stations:
lg. NBA + m bT ( )
meteorological stations:
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mT
=
. e
a
max,
p
./ The research of Prof., Dr.Ngo Dinh Tuan in the year 1980 for - 10 meteorological stations:
a pT , 1.1.4. Researching, analyzing the factors affecting the design flood flow calculation of the small drainage works on the roads.
- Factors affecting the flood flow of small basins of small drainage works on the roads can be divided into 3 categories: climatic conditions, in particular the rain; buffering surface factors; effects of socio-economic activities of human beings.
+) Under the climatic conditions of Vietnam, the rain is a factor directly affecting the flood flow of small basins and the rain is the cause of flood flows on small watersheds in Vietnam.
+) Buffering surface factors including: geographical location, topographical and geomorphological features, geological and soil conditions, surface features, shape of basin. . . These factors affect the two main stages: decisive to concentrating the flow and loss rate. In addition, geographical location and topographical features affect climate conditions expressed by different climate regions and zones in the country. Topography affects rainfall, flood currents of the basin in both direct and indirect manners. Direct manner: creating heavy rainfall due to the windward, creating the little rainfall due to the leeward. Indirect manner: centralizing water fast or slow due to large or small slope, stream network in the fan shape or feather shape. . .
+) Socio-economic activities of the human beings are today increasingly large with negative or positive influence such as effects causing the phenomena of climate change, sea level rise, changing basin buffering surface factors. It is considered through two factorsd of rain and other padding surface.
- In addition, the design flow of drainage works on the roads Q p is also influenced by the design frequency p. The greater the frequency value p becomes (p = 10%, 20%, 50%,...), the smaller the calculated Qp is and vice versa, it is designed with smaller value p (p = 3%, 2% , 1%, ...), then the greater the calculated Qp is.
- The calculated rain intensity parameter at, p is a general affecting quantity in calculating the design flow of drainage works on the roads because it shows the impacts of all factors affecting the calculation of the
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design flood flow of drainage works on the roads, including the rain factors, factors of padding surface and the design frequency.
+) Indeed: at ,p = Ht ,p / t
./ Precipitation regime in the design zone is decisive to the largest value the calculated period Ht, p , so it affects at, p .
./ Design frequency p affecting Ht ,p , so it affects at ,p. ./ Buffering surface factors affecting the water concentration time parameter t of the basin, so it affects at, p .
Ht,p
I
II
p ,
I
+) Also, unlike the calculated daily rainfall parameter Hn,p , then the calculated rain intensity parameter at, p also reflects the influence of rain shape.
H
p ,
I I
p , n
H
H
t t
rainfall in t
0 t Figure 1.4: Influence of the rain shape to the rain intensity at, p
Figure 1.4 shows that despite the same calculated daily rainfall Hn,p , in the two rain regions I and II, they have different shapes, then the the highest calculated period Ht, p in two different areas of rain and as a result, the calculated rain intensity at, p = Ht ,p/t is also different.
- Thus, the limited intensity formula used to calculate Qp for the
small drainage works already has a general affecting parameter at, p 1.2. Shortcoming issues at the thesis to be focused on the settlement.
- Through the above analysis and evaluation, the most urgent existing problems in computing the design flow of small drainage works on the roads in Vietnam today is the determination of the rain parameters in formulars calculating Qp of small drainage works on the roads. Because the currently used parameters were set in previous, they are not matched with the computational requirements Qp of small drainage works on the roads in the weather and climate conditions in Vietnam today.
- Zoning rain (too wide and for long time) as used in the applicable design standard TCVN9845:2013 [5] is not suitable for the computational requirements Qp of small drainage works on roads under
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the present conditions in Vietnam and it is necessary to propose the researches for correcting.
- The calculated rain intensity parameters are of the general and representative characteristics for the rain regime and the shape of the rain zone, for the specific watershed buffering surface, the water concentration time and design frequency, it is characterized by the distinct climates of Vietnam, so it is necessary parameters for calculating the design flow of small drainage works on the roads, reflecting more closely the condition climate and terrain of Vietnam. It is necessary to research and determine the calculated rain intensity parameter aT,p under the climatic conditions of Vietnam used to determine the design flow of small drainage works on the roads Qp in order to ensure the required level of precision.
Chapter 2: STUDYING RAIN CHARACTERISTICS UNDER THE EFFECTS OF THE PHENOMENON OF CLIMATE CHANGE IN COMPUTING THE DESIGN FLOW OF SMALL DRAINAGE WORKS ON THE ROADS
2.1. Overview of Vietnam climatic conditions.
- Vietnam is within the humid tropical, monsoon climate. The annual rainfall and rain duration are relatively large, averaging from 1100 - 8000 mm/year and from 67-223 days of rain/year, compared with countries in the same latitude, it is about 2.4 times higher [25].
- The rainfall regime in Vietnam is under the effect of three main factors:
(i) Weather forms of raining amd raining causes (ii) Wind (iii) Topography.
2.2. Introduction about the network of meteorological stations and rain gauge data sources in Vietnam.
-
According to sources of the National Centre for Hydrometeorological Forecasting, at present, the whole nation has more than 800 rain gauge points (including meteorological stations, meteorological stations and rain gauge sites are operating) distributed
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‡
throughout the territory, reaching the national average density of approximately 433 km2/rain gauge point. Self-recording rain gauge equipments have been present at most meteorological stations, accounting for about 20% of the total rainfall stations, each province has 1 meter meteorological station with self-recording rain gauge machine, 2-3 stations, remaining rain gauge points some provinces have up to ‡ have only daily rainfall measuring equipments.
- For the time of observation: in the north, there are uniform monitoring data from around the year 1960 onward; in the south, due to historical circumstances, continuous and reliable monitoring data are from the year 1980 now.
- In the thesis, rain gauge data is collected from 1960 - 2010 (stations in the North Vietnam), from 1980 to 2010 (stations in the South Vietnam). The sequence of research data is 30-50 years long, so results ensures the necessary reliability. 2.3. Studying rainfall variability features under the effect of the phenomenon of climate change and its effects over calculating the design flood peak flow of small drainage works on the roads.
The study was carried out over 7 norms related to the calculation of
the design flow of small drainage works on the roads as follows. 2.3.1. The rainy season, dry season.
- To distinguish the rainy season, dry season in the year, the thesis used “excess loss norms” [34]. According to this criterion: the rainy season is the season including continuous months with the rainfall exceeding losses (usually taken as 100mm/month, according to the study [34]) with the exceeding frequency p‡ 50%.
100 mm/month } ‡ 50%. That is: p{ (Hmonth)i ‡
- Research findings about the rainy season in the year in the sequence of actual rainfall records in 1960 - 2010 at 12 selected typical meteorological stations are as in Table 2.2 below. Recognizing that in general, the rainy season in Vietma does not have the shift, the change compared with the results of previous studies, however, there have been fluctuations in recent years.
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2.3.2. Rainy months with many days and few days.
- To classify the rainy month with many days, use the classification coefficient
Krain-for-many-days = the number of rainy days in the month/30
0.5 - The month with many rainy days: Krain-for-many-days ‡
Month with many rainy days in the
Rainy months in the year
year (average)
(average)
Meteorological stations,
No.
places
Rainy
Months
Time of appearance
Time of rainy season
1 Muong Lay Town Station
4 months
August
September
2 Tuyen Quang City Station
6 months
August
months 6 months April fi April fi
October
3 Lang Son City Station
4 months
August
September
4 Lang Station-Hanoi
6 months
August
6 months
October
5 Ha Dong Station-Hanoi
6 months
August
6 months
October
6 Son Tay Town Station-
6 months
May fi March fi May fi March fi March fi March fi
August
7 months 5 months May fi May fi May fi May fi
6 months
October
Hanoi
7 Vinh City Station
4 months
March &
4 months August fi
November
October
8 Dong Hoi City Station
December
November
9 Da Nang City Station
December
4 months August fi 5 months August fi
December
10 Nha Trang City Station
February fi September fi 4 months September fi 4 months September fi 4 months September fi
December
6 months
December
11 Buon Ma Thuat City Station
6 months
October
October
12 Can Tho City Station
7 months
May fi May fi
November
July fi May fi 6 months 7 months May fi
November
Table 2.2: Summary of research findings of the month with many rainy days, comparing the research findings of months of the rainy season at 12 meteorological stations selected for studies from 1960-2010
- Comments: The months of the rainy season is not necessarily the month with many rainy days and vice versa. This shows that the rainfall not spread in the rainy days, but focuses on some heavy rains.
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2.3.3. The trend and the variability in the annual rainfall and rainy days in the year
- Using the average trend line and double sliding average line of 5 years to study the trend and the variability by the time of the survey precipitation value. Figure 2.1, Figure 2.2 below are examples of the trend of variation of annual rainfall and the number of rainy days in the year at Lang Station-Hanoi City from 1960 to 2010.
y
y
3
1
3
1
2
2
x
x
1-Actual measurements; 2-Average trends; 3-Double sliding average of 5 years Sudden big values appeared in recent years
- Comments: In all 12 research stations, in recent years, the variation of annual rainfall Hyear and the number of rainy days become greater, more different and more unusual, appearing extremely big values in recent years.
Figure 2.1: Variation trends in annual rainfall Hannual at Lang Station-Hanoi City from 1960 - 2010
Figure 2.2: Variation trends in the number of rainy days in the year at Lang Station-Hanoi City from 1960 - 2010
‘‘ ’’
- 17 -
max and the max. The extreme
y
y
1
1
2
3
2
3
x
x
2.3.4. Trends and variability of the biggest daily rainfall Hday biggest calculated rainfall intensity in the year a T sudden variation due to effects of the climate change phenomena.
1-Actual measurements; 2-Average trends; 3-Double sliding average of 5 years Sudden big values appeared in recent years
max
Figure 2.3: Variation trends Hday
Figure 2.4: Variation trend aT
max at
at Lang Station-Hanoi City from 1960 - 2010
T= 60ph at Lang Station-Hanoi City from 1960 - 2010
max and aT
max and aT
max is not identical, the variability of H24h
- Purposes: comparing and clarifying the rules of change in two important rain parameters in calculating design flood flow of small max , assessing the difference drainage works on the roads Hday between them. This research is especially needed to determine the calculated daily rainfall Hn,p according to the design frequency and calculated rain intensity interval aT,p at the design frequency in chapters 3 and 4 in handling issues of heavy rain. In addition, from this study, it also suggests proactive measures to respond to climate change phenomena in computing the design of small drainage works on the roads today in Vietnam.
- Research results: realized at all 12 research stations, parameters max are constantly changing and not even; in some times, max and aT Hday there are sudden significant changes in recent years. At the same station, max are different, the trend and level of time-variaton trend of H day max and the highest 24-hour rainfall in the year the variability of Hday max is not identical to that of H24h max at other short computational interval the highest rainfall in the year HT T.
‘‘ ’’
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max, aT
max occurs at all research stations. The extreme segment are in both values and time of appearance.
+) The extreme interval suddeness of Hday
max)*, (aT
max)* are suddenly big exceeding values Hn,p , aT,p at the design frequency usually used for small drainage works p = 4%, even exceeding the value at p = 1%.
max)*, (aT
max)*, (aT
./ Extremeness in value: values (Hday
./ Extremeness on the appearance time: the extreme value max)* can occur at the time which is considered to be in the (Hday max)* is extremely dry season. Even the time when the value (Hday big at the same station, they are not coincided. For example, for Lang Station-Hanoi City from 1960 - 2010, the time of appearing the value max)* was on 31 October 2008, but the time of appearing the value (Hday max)* on 03 May 2005, while in the max)* was on 03 May 2005, (a30ph (a20ph max created fell on 27 year 2005, the highest daily rainfall in the year Hday September 2005. Therefore, with the arrival of rain heavy rain intensity although mutations do not create value in the largest daily rainfall, does not create large daily rainfall values are still causing mutations major flood surge for small drainage structures on roads due to the small basin of small drainage works on the road a short time focus countries. This is of particular concern in the design calculations minor drainage works on the road.
+) The change of the highest rainfall in the year Hday
max.
max and aT
max, the rain max in recent years intensity of the highest calculated interval in the year aT make the value Hn,p , aT,p under the frequency set with the sequence of the actual rain measuremens collected up to 2010 tend to increase compared with the calculation result Hn,p , aT,p with the sequence of actual rain measurements up to years backward and results make the calculated value Qp increase. 2.3.5. Average value in many years ‘ X and scattering coefficient Cv, h ệ bias coefficient Cs of Hday
max, aT
- Purposes: This research serves for computing and defining H n,p , aT,p under the design frequency in chapters 3 and 4 in estimating statistical parameters; in determining the years of necessary observation and sampling nyc to ensure the sampling error because the more statistical max have the coefficient Cv, the longer the required sequences Hday
max that we need to research, compare and clarify.
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years of observation nyc are in order to ensure the calculated results Hn,p, aT,p are reliable. The rate Cs / Cv is also a condition for making decision on selecting a suitable probability distribution rule when calculating and determining Hn,p , aT,p to gain the best results. In addition to values ‘ X, Cv, Cs, they also relect the nature of change by the time of the parameter Hday
max.
max, aT - Research results at 12 meteorological stations from 1960 - 2010: the highest daily rainfall has the average value ‘ Hday max from 89.31 - 237.46 mm, coefficient Cv = 0.24 - 0.55, Cs = 0.34 - 2.99, Cs/Cv = 1.4 - max at intervals T = 5mins – 5.7; the highest rain density in the year aT 1440mins with the average value ‘ aT max from 3.01 - 0.07 mm/min, Cv = 0.18 - 0.63, Cs = (-0.25) - 3.58, Cs/Cv = 0.05 - 8.0, with the same station max , the shorter intervals T are, the smaller they coefficients Cv, Cs of aT have values and vice versa. 2.3.6. Cycle of large-small-medium changes of Hday
max and aT
max, aT
max, aT
max, aT
+/ Time of high values: (1983 - 1994), (2007 - 2010). +/ Time of small values: (1956 - 1983), (1999 -2007). +/ Average time: (1994 - 1999). +/ With 2 cycles.
- Purposes: This study serves for testing the representation of the max included period of sampling of the statistical data sequence Hday in the calculation of the frequency to determine Hn,p , aT,p in chapters 3 and 4. They are deemed to have the representativeness, reflecting the approximate accuracy in line with the general change rule, then the max must have the number of years in overall sampling period Hday the heavy rain period and some years in the light rain period in succession. Additionally, researching the cycle of changes also reflects max that we need to research compare, the over-time variation of Hday and clarify.
Figure 2.7: Cycle of changing the biggest daily rainfall in the year Hday
max at
Lang Station – Hanoi City from 1960 – 2010
+/ Time of high values: (1996 - 2010). +/ Time of small values: (1986 - 1996). +/ Average time: (1961 - 1986). +/ With 01 cycle.
- 20 -
max at the
Figure 2.8: Cycle of changing the biggest rain intensity in the year aT computational interval T = 30 mins at Lang Station-Hanoi from 1960 – 2010
max, aT
max , we use the - In order to determine the change cycle of Hday standard error comulative line St = S (Ki – 1) v i Kớ i = (Xi /‘ X) as the variable coefficient. On the standard error comulative line St , if the general trends are considered, we will realize there are groups of 5 cumulative lines always rising up corresponding to the heavy rain periods, or declining corresponding to the light rain periods or always in parallel corresponding to the medium rain periods. A rain cycle includes a period of heavy rain and a little rainy period or a period of heavy rain, a period of little rain and a period of continuous rain average. For example, in above Figure 2.7, Figure 2.8.
max, aT
max and aT
max and aT
- Comments: Hday
max.
max change with cycles; the length of a change cycle of them ranges from 20 to 50 years. In the same station, the change max are not the same, at the calculation interval, the cycle of Hday shorter T is, the more different they are and vice versa. With the length sequence of survey data up to 2010 at the selected meteorological max at T = 5mins – 1440mins reach at least 01 stations, Hday change cycle, even >= 2 change cycles. 2.3.7. Correlation of changes in value and time of together appearance of Hday
max and aT
max.
max and aT
- Comparing the change in values: using the graph standards to compare the variation coefficient Ki of Hday
TT N¨ m
a 10' Ngµy th¸ ng
a 5' Ngµy th¸ ng
a 30' Ngµy th¸ ng
a 20' Ngµy th¸ ng
a 60' Ngµy th¸ ng
a 720' Ngµy th¸ ng
a 360' Ngµy th¸ ng
a 540' Ngµy th¸ ng
a 180' Ngµy th¸ ng
Hngµy Ngµy th¸ ng
a 1080' Ngµy th¸ ng
- 21 -
Figure 2.9: Graph comparing the change in values between Hngày
max at the calculation
max and aT
interval T = 5 fi
1440mins at Lang Station-Hanoi from 1960 - 2010
max: assessed with the color table.
- Comparing the appearance time within the same date in the year of max and aT
max from 5 fi
max and aT
a 1440' Ngµy th¸ ng 1 1961 21 10 15 4 15 4 15 4 30 7 30 7 30 8 30 8 30 8 30 8 30 8 21 10 2 1962 9 5 9 5 9 5 9 5 9 5 9 5 9 5 9 5 9 5 9 5 9 5 9 5 3 1963 17 8 13 10 13 10 13 10 2 6 2 6 17 8 17 8 17 8 17 8 17 8 17 8 4 1964 3 7 1 6 1 6 1 6 1 6 13 8 2 6 3 7 3 7 3 7 3 7 3 7 5 1965 24 7 31 7 31 7 12 6 12 6 12 6 24 7 24 7 24 7 24 7 24 7 24 7 6 1966 28 10 3 6 3 6 3 6 3 6 3 6 3 6 27 10 27 10 27 10 27 10 27 10 7 1967 25 7 9 7 9 7 9 7 9 7 9 7 9 7 9 7 9 7 9 7 24 7 24 7 8 1968 14 8 6 6 6 6 6 6 6 6 6 6 31 8 31 8 31 8 13 8 13 8 13 8 9 1969 11 6 8 6 8 6 8 6 8 6 10 6 1 6 1 6 1 6 10 6 10 6 10 6 10 1970 25 7 3 7 3 7 30 8 30 8 30 8 14 5 25 7 25 7 25 7 25 7 25 7 11 1971 12 5 16 9 16 9 16 9 16 9 16 9 12 5 12 5 12 5 12 5 12 5 12 5 12 1972 23 8 14 7 14 7 22 8 22 8 14 8 22 8 22 8 22 8 22 8 22 8 22 8 13 1973 24 7 27 4 27 4 27 4 27 4 24 4 23 7 23 7 23 7 23 7 2 9 2 9 14 1974 7 9 4 7 4 7 4 7 4 7 7 9 7 9 7 9 7 9 7 9 7 9 7 9 15 1975 21 9 10 8 10 8 10 8 15 7 21 9 21 9 21 9 21 9 20 9 20 9 20 9 16 1976 17 9 17 9 17 9 30 6 30 6 17 9 17 9 17 9 17 9 17 9 17 9 17 9 17 1977 15 7 15 7 15 7 15 7 15 7 15 7 15 7 15 7 15 7 15 7 15 7 15 7 18 1978 22 9 17 5 17 5 17 5 17 5 22 9 22 9 22 9 22 9 22 9 21 9 21 9 19 1979 4 8 1 9 1 9 16 9 16 9 1 9 3 8 3 8 3 8 3 8 3 8 3 8 20 1980 19 8 8 8 8 8 18 10 18 10 8 8 8 8 8 8 8 8 19 8 19 8 19 8 21 1981 12 6 23 4 23 4 6 9 6 9 6 9 4 10 4 10 4 10 20 8 20 8 12 6 22 1982 10 7 20 7 20 7 20 7 20 7 20 7 9 8 20 8 20 8 10 7 10 7 10 7 23 1983 4 10 21 6 21 6 21 6 21 6 21 6 18 7 18 7 18 7 18 7 3 10 3 10 24 1984 10 11 18 9 18 9 18 9 18 9 18 9 10 11 9 11 9 11 9 11 9 11 9 11 25 1985 12 9 18 6 18 6 27 7 27 7 27 7 27 7 12 9 12 9 12 9 12 9 12 9 26 1986 18 6 18 6 18 6 18 6 18 6 18 6 18 6 18 6 18 6 18 6 18 6 18 6 27 1987 30 8 25 9 25 9 25 9 28 5 28 5 28 5 28 5 28 5 25 7 25 7 25 7 28 1988 23 10 8 7 8 7 6 8 6 8 6 8 6 8 6 8 3 10 3 10 3 10 3 10 Hday 29 1989 12 6 11 6 11 6 11 6 11 6 11 6 11 6 11 6 11 6 11 6 11 6 11 6 30 1990 20 9 27 3 27 3 27 3 20 7 27 3 27 3 27 3 31 5 20 9 19 9 19 9 31 1991 11 6 7 5 7 5 7 5 7 5 7 5 7 5 7 5 11 6 11 6 11 6 11 6 Table 2.9: Color table of assessing the duplication in appearance time at the 32 1992 30 6 10 5 10 5 10 5 10 5 10 5 29 6 29 6 29 6 29 6 29 6 29 6 33 1993 30 9 2 5 2 5 2 5 2 5 29 9 29 9 29 9 29 9 29 9 29 9 29 9 1440mins at Lang Station- same date in the year of Hday 34 1994 20 5 7 7 7 7 7 7 7 7 7 7 7 7 20 5 20 5 19 5 19 5 19 5 35 1995 31 8 14 6 14 6 14 6 14 6 9 9 12 8 12 8 30 8 29 8 29 8 29 8 Hanoi from 1960-2010 (the same color is the duplication) 36 1996 5 11 19 4 19 4 16 4 19 4 19 4 19 4 5 11 4 11 4 11 5 11 5 11 37 1997 15 8 9 5 9 5 9 5 9 5 9 5 15 8 15 8 15 8 15 8 15 8 15 8 38 1998 26 6 2 6 2 6 2 6 2 6 9 6 25 6 25 6 7 6 7 6 7 6 7 6 39 1999 15 7 15 7 15 7 15 7 15 7 15 7 15 7 15 7 15 7 14 7 14 7 14 7 40 2000 27 8 8 7 8 7 8 7 8 7 4 10 4 10 4 10 4 10 4 10 4 10 4 10 41 2001 3 8 22 7 22 7 22 7 22 7 22 7 22 7 22 7 22 7 2 8 2 8 2 8 42 2002 1 8 7 6 7 6 7 6 7 6 7 6 7 6 7 6 7 6 7 6 7 6 1 8 43 2003 25 5 5 6 5 6 5 6 5 6 5 6 24 5 24 5 24 5 24 5 24 5 24 5 44 2004 21 7 26 6 26 6 17 8 17 8 17 8 27 6 27 6 26 6 27 6 27 6 21 7 45 2005 27 9 3 5 3 5 3 5 3 5 3 5 22 8 22 8 26 9 27 9 27 9 27 9 46 2006 18 8 5 9 5 9 5 9 5 9 5 9 20 11 20 11 17 8 20 11 20 11 17 8 47 2007 27 9 26 8 26 8 26 8 26 8 26 8 26 8 27 9 27 9 27 9 27 9 27 9 48 2008 31 10 15 7 15 7 15 7 15 7 15 7 15 7 17 7 30 10 31 10 31 10 31 10 49 2009 17 7 20 7 20 7 20 7 20 7 20 7 20 7 20 7 17 7 17 7 17 7 17 7 50 2010 13 7 13 7 13 7 13 7 13 7 13 7 13 7 13 7 13 7 13 7 13 7 13 7 88% *
14% 22% 44% 58% 68%
14% 14% 14%
Trï ng lÆp:
76%
78%
max and aT
max) and Hday
max = T.aT max (HT
max) and Hday
max) and Hday
- 22 -
- Comments: the change in the highest daily rainfall in the year max and the parameter of the highest rain interval intensity in the year Hday max in the same station have no the entire duplication, but the difference, aT even very difference. This difference occurs in all aspects: variation trends, change cycles, level of variation and coefficients Cv, Cs, time of together appearance on the same date in the year, . . . . This difference max depends the calculation interval T: at the between Hday calculation intervals, the smaller T is, the higher the difference between max is, the more reduced the difference max (or HT aT max becomes when calculating the rising between aT interval T, however, up to the value T = 24h, then the interval between max does not reach the entire duplication, but max (or H24h a1440ph still has the difference.
When determining the flood flow of small basins of small drainage works on the roads, generally calculated in the segment of small interval T because the water concentration time t of the small basin is usually short; if the parameters of daily rainfall are used to calculate, it may miss
- 23 -
periods with heavy rain intensity or fail to review the rain with the high strength, but not with the highest daily rainfall. And thus, to improve the accuracy in calculation of the flood flow at small basin of small drainage works on the roads, better reflect the climatic and topographical conditions in Vietnam, directly use parameters of rainfall intensity to calculate.
Chapter 3: DETERMINING THE CALCULATED DAILY RAINFALL AND RESEARCHING CHARACTERISTIC RAIN SHAPE PARAMETERS
3.1. Defining the calculated daily rainfall under the design frequency Hn,p. 3.1.1. Background.
max
L y m u và ki m đ nh m u th ng kê l ị
ượ
ư
ể
ấ
ẫ
ẫ
ấ
ngày
ng m a ngày l n nh t năm H ớ ự ế
ể
ạ
- Hn,p is now the rain parameter used to calculate Q p of small drainage works under the standard TCVN9845:2013 [5], even it is also used to calculate Qp% of the medium and large basins because in the current conditions of Vietnam, daily rain measurement data is very popular, widespread nationwide, sufficient and continuous in many years.
ể ./ Ki m tra sai s l y m u ẫ ./ Ki m tra th i kỳ l y m u ẫ ờ
ấ
X lý m a đ c bi
ư ặ
ử
t l n ệ ớ
ầ
ấ
Tính t n su t kinh nghi m: ệ ./ Công th c kỳ v ng ứ
ọ
Tìm đ
ng t n su t lý lu n phù h p:
ườ
ầ
ậ
ợ
ng pháp đ
ng thích
ườ
ng t n su t lý lu n phù h p theo ph ậ
ấ
ợ
ươ
ườ
ấ ./ Hàm phân b ố Kritski - Menkel (K-M) ./ V tìm đ ầ ẽ h pợ
ể
ợ ủ ườ
ự
ệ
ầ
ấ
ậ
ớ
ị ./ S d ng tiêu chu n
Ki m đ nh s phù h p c a đ ự ử ụ
ng t n su t lý lu n v i tài li u th c đo: ể
ẩ ki m đ nh Smirnov - Kolmogorov
ị
- The most sufficient database Hn,p in [5] was established in 1987, since then now, it has passed over 25 years, the value Hn,p has been changed much due to the changed rain regime, especially the change in recent years due to effects of the climate change phenomena. Therefore, it is necessary to set up the new database Hn,p in line with weather ố changes in Vietnam to be used in calculating Qp of drainage works on the thu th p th c t ậ roads. 3.1.2. Defining the calculated daily rainfall Hn,p under the design Ki m tra tính đ i bi u: frequency p. ể ố ấ ể
- 24 -
Figure 3.1: Chart determining the calculated daily rainfall Hn,p with the statistical analysis of daily rain measurement sequence at rain gauge stations in Vietnam, often continuous.
3.1.3. Results of defining the calculated daily rainfall Hn,p under the design frequency p for 12 meteorological stations, comments and proposals.
- Applying the diagram in Figure 3.1 calculated set value Hn,p at 12 meteorological stations selected for study day rainfall data series collected in practice from 1960 to 2010 to ensure results reliability required design, R reliable ‡ 95%, consistent with the characteristics of the rainfall regime in the situation of our country in the current climate is affected by the phenomenon of climate change.
- When comparing the value of Hn,p , the dissertation prepared with rainfall records up to 2010 with a value of Hn,p established in [5] with rainfall records to 1987 noticed: after 23 years, from 1987 - 2010, in all meteorological stations in the study regions across the country, the value of Hn,p in the frequency change very much. At the level of p smaller the larger the change often, sometimes increased by a factor of 1.5 - 2 times, the greater the level of p less disparity. The results of this comparative study in accordance with the laws of change of rain at the weather station made in Chapter 2, there is rain regime in our country has to change and change dramatically the year as of recent.
- 25 -
.
T,p as the characteristic rain shape coefficient at the period T
H
, pT
=
- It is therefore recommended to use daily rainfall data calculated by the frequency of Hn,p up to 12 meteorological stations selected for study since rainfall records from 1960 to 2010 as shown in Appendix 1 to calculate Qp of drainage works on the road in the area of the meteorological stations. 3.2. Studying to determin the characteristic rain shape coefficient Y T and proposing the criteria on zoning the rain in line with requirements on calculating the flood flow at the small basins of small drainage works on the roads. 3.2.1. Concepts and features of the characteristic rain shape coefficient function Y - Call Y and the frequency p at any rain zone.
, pT
H
, pn
T,p
Y (3.9)
, pT
- With the theories as well as practices (eg research results on actual rainfall records in the 12 studies selected meteorological stations with rainfall data collected in 1960-2010 in the thesis) have demonstrated that : t rong a rain areas have been identified, they curve relationship Y ~ T at different frequencies p very close together, which means we can see the frequency does not depend on p anymore. So they took averages T,p ~ T in the frequency p to represent the rain, the moving of the curve Y average is denoted Y T, so Y T depends only on T, does not depend on p, we have the formula (3.10).
H = T H
, pn
Y (3.10)
V i:ớ HT,p is the highest rainfall at the calculated period T at the
frequency p Hn,p is the calculated daily rainfall at the frequency p T is the calculated rain period. When calculating Qp take T = t .
- The function Y T taking the distinctly different rainfall areas, the T ~ T to T ~ T will use different roads relations Y relationship curve Y partition the rain. The factor Y T reflects the shape of the rain: review Figure 1.4 in two rain areas I and II with the same calculated daily
- 26 -
II, so it is possible T =
HT,p
I „ rainfall Hn,p , but rain shapes are different, so HT,p to use the ratio (HT,p / Hn,p) to characterize the shape of the rain and Y HT,p / Hn,p is called the characteristic rain shape coefficient. 3.2.2. Purposed and significance of researching and defining the characteristic rain shape coefficient Y T.
T was used to determine the highest rainfall in periods calculated HT,p at a frequency from Hn,p according to frequency, HT,p = Y T.Hn,p , used in the flow calculation formula Sokolopsky designed for medium and large basins, it is also important parameters in calculating showers-flows with NAM-MIKE model with reliable results.
- To determine the Qp small drainage works on standard road TCVN9845: 2013 [5], in addition to determining the parameters H n,p as in Section 3.1 above, also need to determine the value of the coefficient characteristic shape rains Y T in T periods calculated for wet areas suitable design and update the happenings of rain to the present time in Vietnam. - At the same time, the coefficient Y
T ~ T is a
T is one
- In addition, the characteristic rain shape coefficient Y very important parameter used in the rain zoning. - From the above analysis, the researchers identified factors Y of the research content with practical scientific significance.
3.2.3. Results of building the characteristic rain shape coefficient Y T for 12 studied meteorological stations, comments and suggestions.
- The sequence number of actual rainfall records collected since 1960 - 2010 in 12 studied selected meteorological stations, the value Y T can be set with very low tolerance under the evaluation criteria of World 2 , are Meteology Organization (WMO) using the effective criteria Ruseful reaching the pretty, good levels.
T in the periods T = 5minsfi
Y
- Recommendations for using the characteristic shape rain coefficient 1440mins set with actual rainfall records since 1960 to 2010 at 12 meteorological stations in the Appendix 2, to calculate the design flow of drainage works on the roads in this area.
- 27 -
3.2.4. Proposed criteria, rain zoninging methods suitable for calculation requirements for the flood flow of small basin of small drainage works on the road.
- In practical calculations, the area of the territory assigned to the wet areas and the construction of the average value of the characteristic parameters of rain across the region to use for all areas within the basin That rain. Because to do so is not in any position catchment area has always put rain gauges.
- Results of the rain zoning have a relatively large impacts over the accuracy of the resulting Qp of small drainage works on the road. The partitioning of rain today in our country, even rain zoning is used in the design criteria [5] is considered too broad, not suitable for the computational requirements of small basins, flood flow of small drainage works on the road. The distribution of the large rain area has turned too wide average value of the characteristic parameters of rain across the region, causing loss of particular features of the small catchment area of small drainage works on the road . Also according to the study Chapter 2, rain regime in our country so far have been significant changes in recent years due to increasingly affected by climate change.
[Ruseful
2 .
2]cp select larger the partition results in as much detail 2]cp not less than 40% selected the minimum
- The thesis has recommended and proposed methods and criteria on the consistent rain zoning for computing requirements of small basins, flood flow of drainage works on the roads as follows: The base zoning rain The main criterion is the characteristic function coefficients rains T ~ T, ie relations philosophy reduced rainfall intensity shape Y calculated according to the duration, the degree of error when calculating the partition between the values ( Y T,p)k in positions k in the rain than average value Y T characteristics for the rain must not exceed the 2 ‡ 2 ]cp , and combined with a tolerance level, ie to ensure the Ruseful meta-analysis of factors affecting mode causes floods as torrential rains, the rainy season, topographical features. +) With this method partitions can be quantified level of rain zoning error when the criteria of effective Ruseful
+) Value [Ruseful and contrast, values [Ruseful prescribed level achieved by WMO.
- 28 -
+ Example on application: partition implemented for Ha Noi with actual rainfall records from 1960 -2010 of 3 stations at Lang, Ha Dong, 2 ]cp = 85% , in accordance with the criteria Son Tay Town with the [Ruseful of the WMO at the Good rate, then Hanoi City is divided into two regions rain: rain areas including urban districts and the districts of southern plain terrain and wet areas including Son Tay town and districts with the semin-mountainous terrain.
Chapter 4: STUDYING AND DETERMINING THE RAIN INTENSITY PARAMETERS IN CALCULATING THE DESIGN FLOW OF SMALL DRAINAGE WORKS ON THE ROADS IN VIETNAM
4.1. The direct method determining the calculated rainfall intensity aT,p.
This method results in accurate determination aT,p, but it is only used when having actual recording rain gauge data at the design area with long-enough years up to the time of designing the work. 4.1.1. Case of continuous actual self-recording rain gauge data at the meteorological stations. The direct calculation aT,p similar in the calculation chart in Figure
3.1 4.1.2. Case of interrupted actual self-recording rain gauge data at the meteorological stations or some years of observation. In this case, determining aT,p with the statistical analysis method is in accordance with the chart in the following Figure 4.4.
Figure 4.4: Chart determining the calculated rain intensity aT,p at the interval T and the frequency p with the statistical analysis in the case of self-recording rain gauge data at meteorological stations which is long enough, not continuous, interrupted in some observation years
- 29 -
4.2. Determining the calculated rain intensity aT,p based on the calculated daily rainfall Hn,p and characteristic rain shape coefficient Y
T.
=
a
. H
, pT
, pn
T T
Y (4.3)
+
S
p
=
=
a
, pT
The indirect method is used when the material conditions for self- recording rain gauge whether or not there is a lack, not long enough to be able to apply methods of direct calculation. This method allows to take advantage of resources measured daily rainfall data are fully available, continuous, long enough for all rain gauge stations nationwide to calculate aT, p when Y T is available in the rain zone. 4.3. Building the formula to define the calculated rain intensity aT,p by the rain strength feature and rain shape coefficient. 4.3.1. Analyzing and selecting the experimental formula form and regression method to define the value of coefficients in the calculated rain intensity formular aT,p. - Select the basic formula to determine the calculated rain intensity
m
T
lg. NBA m T
aT,p at the period T and frequency p:
- 30 -
- The basic formula has the advantage of simplicity in calculations, advantages of regression analysis to find the value of the coefficients in the formula and calculation results while maintaining tolerance. 4.3.2. Determining the rain shape coefficient m for the rain zone and determining the rain strength Sp by the frequency in the rain zone.
- From the basic formular, we have: aT,p = Sp / Tm +) Take the logarithm base 10 at two sides, we have: lgaT,p = (- m).lgT + lgSp
+) Set: y = lgaT,p ; x = lgT ; c = -m ; d = lgSp +) Thus, there is a line equation form: y = c.x + d , implement the regression for the line equation form, get the rain shape coefficient m = - c and the rain strength Sp at the frequency p is Sp = 10d. - Rain form factor established for the whole region at all levels rain
+
=
=
+
lg.
N
a
, pT
frequency p should apply regression focus methods to find m. 4.3.3. Determining the climate zone coefficients A, B for each rain zone.
lg. NBA m T
B m T
- From the basic formula, we have: A m T
+) Set: y = aT,p ; x = lgN ; c = B / Tm ; d = A / Tm +) In one rain zone, A, B, m are constant. Therefore, at the same value and period T, then: c = const, d = const.
+) Got the line function form: y = c.x + d. Perform the regression of this function to get c and d, then find out factors A and B at periods T: A = d.Tm , B = c.Tm
- Values A, B are generally established for the whole rain zone at
S
p
=
a
every period T, so it is taken the average. 4.3.4. Formular calculating the rain strength Sp and rain shape coefficient m.
, pT
m
T
- The formular has the form: (4.10)
- Belong to the indirect method form. Used in case of rain gauge material fact with self-recording rain gauges are not available or missing, not long enough, even in the case of daily rainfall data measured no or
- 31 -
ng đ m a tính toán a
T,p theo h s vùng
+
=
a
, pT
ệ ố ườ ứ missing, not long enough, but knowing the form factor of rain m and rain strength Sp at frequency p. 4.3.5. Công th c tính c khí h u A, B và h s hình d ng c n m a m. ệ ố ộ ư ơ ư ậ ạ
lg. NBA m T
- The formular has the form: (4.11)
- Belong to the indirect method form. Used in case of rain gauge material fact with self-recording rain gauges are not available or missing, not long enough, even in the case of daily rainfall data measured no or missing, not long enough, but knowing the rain shape factor m and climate zone coefficients A and B of the rain zone. 4.4. Surveying the relation of the rain strength Sp under the frequency and calculated daily rainfall Hn,p under the frequency in the same rain zone.
- Researching and surveying data measuring actual rain at the meteorological stations in Vietnam showed in the same rain area, the rain strength Sp at the frequency p and the calculated daily rainfall Hn,p at the frequency p correlates relatively closely with the following formula (for example in Figure 4.6).
S
.a=
H
p
, pn
y = Sp
(Sp ~
Hn,p)
Sp =a
.Hn,p
is the regression coefficient of the climate zone, depending In which: a on the rainy season.
- 32 -
Figure 4.6: Regression results of finding out the regression factor of the
climate zone a
for Lang Son City station with the rain gauge data collected
.
from 1960 - 2010 - Method of determining the coefficient a +) Set: y = Sp ; x = Hn,p ; c = a +) get the line relation form: y = c.x +) Perform the regression for the line form y = c.x, we have the
factor c, then find out the regression factor of the climate zone a = c.
, pn
=
a
- Formular calculating the rain strength aT,p under the regression factor of the climate zone a , the rain shape coefficient m and the calculated daily rainfall Hn,p.
, pT
H m
.a T
(4.15)
- Belong to the indirect method form. Used when self-recording rain gauge material fact or lack of, is not long enough, while knowing the shape factor m rain, the regression coefficient of climates a of the rain. This method allows to take advantage of resources measured daily rainfall data are fully available, continuous, long enough in the rain gauge stations nationwide. 4.5. Determining the calculated rain strength aT,p under the standard rain strength aTo,p.
m
- The calculated rain intensity parameter aT,p is a quantity which much
depends on the specific parameters of climates. If in the formula aT,p there
is a parameter that can be integrated and characterized for the parameters
of the rain will improve the accuracy of the calculated results. Synthesis
parameters in a formula T, p is chosen as a standard rain intensity aTo,p . It is
the rain intensity at frequencies p calculated with standard rain periods T0
of the rain zone. T0 is chosen as follows: T0 = 20 min when calculated in
period T £ 20’, T0 = 60 min when calculated at periods 20’
=
a
a
, pT
pT , 0
T 0 T
(cid:246) (cid:230) (cid:247) (cid:231) (4.16) ł Ł
- 33 -
- Thus, using the formula (4:16) can be calculated rainfall intensity calculated a T, p in time period T and frequency p when just building tables available for some rain intensity values a standard aTo,p at frequency p (3 standard rain periods T0 = 20 mins, 60 mins, 180 mins) and knowing the rain shape factor m in the rain zone while maintaining the required accuracy. 4.6. Determing the calculated rain strength aT,p with the method of using the stations.
- The basis of the method. +) As indicated, the basis for partitioning the similarity rain regime, rainfall characteristics between the rain gauge point. In the same characteristics of the rain, the rain in the position difference less, are considered to be constant. The coefficients Y T , m is the characteristic parameter for rain in a region characterized by rain should be considered not change, at the same location in the same area rain.
+) Based on these characteristics, can determine rainfall intensity at a station to know the rainfall intensity at neighboring stations in the same region in the rain. Station adjacent to the base station known as lean, leaning station to station is fully self-recording rain gauge data over many years n monitoring and continuous mode, very similar rainfall characteristics stations should take into account.
H
2 pn ,
a
a
.
2 pT ,
1 pT ,
H
1 pn ,
- Formula determining the calculated rain strength aT,p with interpolation stations in accordance with the calculated daily rainfall Hn,p. (cid:246) (cid:230) (cid:247) (cid:231) @ (4.17) (cid:247) (cid:231) ł Ł
S
2 p
a
a
.
2 pT ,
1 pT ,
S
1 p
- Formula determining the calculated rain strength aT,p with interpolation stations in accordance with the rain strength feature Sp. (cid:246) (cid:230) (cid:247) (cid:231) @ (4.18) (cid:247) (cid:231) ł Ł
In the above formulas, ‘‘2’’is the station to be calculated; ‘‘1’’is the dependent station.
- The method using the dependent stations determines the calculated rainfall intensity aT,p at the station without self-recording rain gauge data,
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only daily rainfall data measured (4:17 formulas) or is used to calculate, effective adjusted results define a calculated rainfall intensity aT,p at the station that recorded rainfall records themselves or with a short remaining years of observation (formulas 4.17 or 4.18), while available seat in a station with the rain zones. 4.7. Assessing tolerance of formulas aT,p. Comments and proposals.
- The evaluation of the error of the empirical formula (4.3), (4:10), (4:11), (4:15), (4:16), (4:17), (4:18) features a rainfall intensity calculated 2 and assessment criteria of the WMO. T, p : use of norms for effective Ruseful - Evaluation results show that: all of a formula T, p are achieved on 2 ‡ 40%, the minimum level specified ''Passed'' of World Ruseful Meteology Organization. Thus, the empirical formula can be used to indirectly determine the rainfall intensity parameters calculated a T, p in the case of different databases rain may have been in the design , used to calculate the Qp of small drainage works on the road.
- Errors of different formulas in different rainfall areas. It depends on the rainfall regime regions. There are formulas in the rain for a good result but to the other rain for a normal result, not achieving the optimal level of error. In case eligible to be used at the same time a lot of formulas aT,p in the design zones, so give the priorities to selecting the formula with the lowest tolerance.
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CONCLUSIONS AND RECOMMENDATIONS
Proposing a number of recommendations in the hydrological A- The comments and conclusions drawn from research findings and recommendations. 1) calculations for bridges and culverts in Vietnam as follows.
1.1. It is necessary to regularly update the data on developments rain suit weather conditions to build the parameters for calculating the design flow of drainage works on the roads.
2 ‡
1.2. When calculating the design of small drainage works on the roads outside determined by calculating the frequency of traffic regulations designed Q p% longer need to check further under water level and historical flood flow Qhistorical of the mutations in heavy rain to get the solutions to cope with the phenomenon of sudden rainfall, rainfall intensity and duration appear due to the extreme ng of the climate change phenomenon. This is a new recommendations of the thesis.
[Ruseful
2) Recommending appropriate rain zoning to calculate flow requirements designed small drainage works on the road should be based on the main criteria is characteristic rain shape coefficient Y T ~ T, ie, strength- rain and rain periods calculated, the tolerance level of the 2]gh and analysis partition ensures rain conditions Ruseful combined with synthetic factors affecting processing of rain causes floods as torrential rains, the rainy season, topographical features. Here are proposals with scientific and practical significance to plan for good flood prevention, the first issue is required flood logical partition, in accordance with rainfall characteristics, topographic features of each region. 3) Recommending the use of 7 different experimental formula forms, including formulas (4.3), (4:10), (4:11), (4:15), (4:16), (4:17), (4:18) to indirectly determine the approximate rain intensity parameters calculated a T, p used to calculate Q p small drainage structures on roads in our country in the region where no design is self-recording rain gauge data or have but some year observation point designed to work not long enough so I can not use a direct method for calculating T, p . In the above formula, the formula (4:15), (4:16), (4:18) is the three new improved formulations
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using the recommendations of the thesis, the formula remains the coefficients in the formula are new construction for the area of selected 12 meteorological stations studied. The empirical formula which allows reliability, are used for different conditions on the basis of data available in the rain design, allowing diversification parameters defining a T, p Council allow selected using a formula aT, p for highly accurate results while at the same time are eligible to use a lot of formulas a T, p in the design area.
This issue is of the scientific and practical significance because with the conditions in Vietnam today, the rain gauges measured more but mostly daily rainfall, construction issues indirectly formulas intensity rain calculate aT,p; study the problem moved from calculated the amount of rain precipitation each calculation period is very short amount required in calculating Qp of drainage works on the roads in Vietnam. 4) Recommendations for calculated daily rainfall values Hn,p under the design frequency in 12 selected meteorological stations on the basis of sequence studies rainfall records actually longer, since 1960 to 2010 (Appendix 1), which is believed to be the last time to the new context of the impact of climate change phenomena, application to calculate Qp of small drainage works on the roads according to the applicable standard TCVN9845: 2013 [5 ], used to determine the rainfall intensity calculated aT,p according to the empirical formula (4.3), (4:15), (4:17), or used to calculate Qp for medium and large basins under the Sokolopsky formula.
For example, some values Hn,p prepared in the dissertation for Lang
1% 402.93 4% 299.19 20% 182.00 50% 99.99% 89.20 122.26 Station-Hanoi. p (%) Hn,p (mm) 10% 230.1 0
Other frequency p levels, other meteorological stations in Annex 1. 5) Recommendations for characteristic shape rain coefficient values Y T prepared for 12 regional meteorological research stations with actual rainfall records since 1960 to 2010 (Appendix 2), used to calculate the intensity rain calculate the concentration time of the basin water and the design frequency empirical formula (4.3), used to calculate the Qp of small drainage works on roads under the stdanrd TCVN9845: 2013 [5].
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At the same time, it is an important parameter used to calculate transition from calculated daily rainfall Hn,p to calculated rain amount at each short time HT,p by the formula (3.10) HT,p=Y T .Hn,p used in the calculation formula Sokolopsky to compute Qp for medium and large basins, showers-flows with the NAM-MIKE model with reliable results. Also, characteristic rain shape coefficient Y T is also used as a criterion to partition the rain.
T set in the thesis for Lang Station-
For example: some values Y
T
Hanoi City: T (ph) Y 5’ 0.087 20’ 0.224 720’ 0.928 180’ 0.577
1440’ 60’ 1.134 0.401 Othe calculation intervals T, other meteorological stations in Annex 2. 6) To recommend the characteristic rain strength values Sp at frequency p = 1fi 99.99% prepared for 12 meteorological research stations with actual rainfall records since 1960 to 2010 (Appendix 5), used to calculate aT,p according to the empirical formula (4:10), (4:18) to calculate Q p of small drainage works on the roads.
For example: some values Sp prepared for the thesis at Lang Station-
1% 13.27 4% 13.48 10% 13.56 20% 13.74 50% 12.49 99.99% 1.72 Hanoi City: p (%) Sp
Other frequency p levels, other meteorological stations in Annex 5. 7) Recommendations for values of rain form factor m, climate coefficients A and B, the regression coefficient of climates a prepared for 12 regional meteorological research stations with actual rainfall records from 1960 - 2010 (Appendix 6), used to calculate aT,p according to the empirical formula (4:10), (4:11), (4:15), (4:16) used to calculate Q p of small drainage works on roads.
For example: some values m, A, B, a prepared for Lang Station- Hanoi City: a
Coefficient name Coefficient value m 0.557 A 4.990 B 7.197 0.032
Other meteorological stations in Annex 6.
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8) Recommendations for standard rain intensity values aTo, p in the standard rain periods T0 = 20 mins, 60 mins, 180 mins and the frequency p = 1fi 99.99% prepared for 12 meteorological stations with the direct method with actual rainfall records since 1960 - 2010 (Appendix 7), used to calculate aT,p under the empirical formula (4:16) to calculate Q p of small drainage works on the road.
For example: some values aTo,p (mm/min) prepared for Lang Station- Hanoi City:
1.84 1.11 0.45 0.62 0.28 0.27 2.31 1.42 0.63 1% 3.33 2.11 1.15 10% 20% 50% 99.99% 2.58 1.61 0.75 p (%) aT0,p at T0 = 20’ aT0,p at T0 = 60’ aT0,p at T0 = 180’
4% 2.91 1.83 0.92 Other frequency p levels, other meteorological stations in Annex 7. 9) Recommendations for the calculated rain flow module qT,p in accordance with the rain strength aT,p (mm/min) [qT,p = 166.67aT,p (liter/s/ha)] used to determine the design flow of the urban drainage works, QP = C.qt ,p.F, under the standard TCVN 7957:2008 [8]. 10) Rain parameters studied and determined in the thesis are used in formulas to calculate Qp for small drainage works on the roads as used now such as (1.9) of TCVN9845:2013 [5] for the outskirt roads, (1.11) of TCVN7957:2008 [8] for urban roads and formulas {for example (1.10), . . .} in calculationhydrology manual of of the Ministry of Transport [3]. In addition, it is also used in the Sokolopsky formula (1:12) in [3] used to calculate Q p for medium and large basins.
The value of the parameter about the rain up to 12 meteorological stations were selected research proposals reference the new supplement or replace the new database is now used for rain in the design criteria [5], [8 ] use the Qp in the region of the current meteorological stations. B- Further research directions. Building the logical rain zoning map with the large percentage to calculate Qp for small drainage structures on roads in each local conditions in Vietnam./.
