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

tration time t of the basin. - Determining the calculated rainfall intensity aT,p based on the calculated daily rainfall Hn,p and characteristic rain shape coefficient YT (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: ./ The research of Prof., Dr. Nguyen Xuan Truc in the year 1980 for 18 meteorological stations: ./ The research of Dr.Tran Huu Uyen in the year 1973 for 34 meteorological stations: ./ The research of Dr.Tran Viet Lien in the year 1979 for 47 meteorological stations: ./ The research of Prof., Dr.Ngo Dinh Tuan in the year 1980 for 10 meteorological stations: 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 Qp 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 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 . +) Also, unlike the calculated daily rainfall parameter Hn,p , then the calculated rain intensity parameter at, p also reflects the influence of rain shape. 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 highest rainfall in the 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. Figure 1.4: Influence of the rain shape to the rain intensity at,p - 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 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 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 ³ 1 meter meteorological station with self-recording rain gauge machine, some provinces have up to ³ 2-3 stations, remaining rain gauge points 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 p³50%. That is: p{ (Hmonth)i ³ 100 mm/month } ³ 50%. - 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. 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 - The month with many rainy days: Krain-for-many-days ³ 0.5 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 No. Meteorological stations, places Month with many rainy days in the year (average) Rainy months in the year (average) Months Time of appearance Rainy months Time of rainy season 1 Muong Lay Town Station 4 months May ® August 6 months April ® September 2 Tuyen Quang City Station 6 months March ® August 7 months April ® October 3 Lang Son City Station 4 months May ® August 5 months May ® September 4 Lang Station-Hanoi 6 months March ® August 6 months May ® October 5 Ha Dong Station-Hanoi 6 months March ® August 6 months May ® October 6 Son Tay Town Station-Hanoi 6 months March ® August 6 months May ® October 7 Vinh City Station 4 months February ® March & September ® October 4 months August ® November 8 Dong Hoi City Station 4 months September ® December 4 months August ® November 9 Da Nang City Station 4 months September ® December 5 months August ® December 10 Nha Trang City Station 4 months September ® December 6 months July ® December 11 Buon Ma Thuat City Station 6 months May ® October 6 months May ® October 12 Can Tho City Station 7 months May ® November 7 months May ® November - 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. 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. - 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. 1-Actual measurements; 2-Average trends; 3-Double sliding average of 5 years ‘‘ ’’ Sudden big values appeared 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 2.3.4. Trends and variability of the biggest daily rainfall Hdaymax and the biggest calculated rainfall intensity in the year aTmax. The extreme 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 Figure 2.3: Variation trends Hdaymax at Lang Station-Hanoi City from 1960 - 2010 Figure 2.4: Variation trend aTmax at T= 60ph at Lang Station-Hanoi City from 1960 - 2010 - Purposes: comparing and clarifying the rules of change in two important rain parameters in calculating design flood flow of small drainage works on the roads Hdaymax and aTmax , assessing the difference 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 Hdaymax and aTmax are constantly changing and not even; in some times, there are sudden significant changes in recent years. At the same station, the trend and level of time-variaton trend of Hdaymax and aTmax are different, the variability of Hdaymax and the highest 24-hour rainfall in the year H24hmax is not identical, the variability of H24hmax is not identical to that of the highest rainfall in the year HTmax at other short computational interval T. +) The extreme interval suddeness of Hdaymax, aTmax occurs at all research stations. The extreme segment are in both values and time of appearance. ./ Extremeness in value: values (Hdaymax)*, (aTmax)* 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%. ./ Extremeness on the appearance time: the extreme value (Hdaymax)*, (aTmax)* can occur at the time which is considered to be in the dry season. Even the time when the value (Hdaymax)*, (aTmax)* is extremely 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 (Hdaymax)* was on 31 October 2008, but the time of appearing the value (a20phmax)* was on 03 May 2005, (a30phmax)* on 03 May 2005, while in the year 2005, the highest daily rainfall in the year Hdaymax created fell on 27 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 Hdaymax, the rain intensity of the highest calculated interval in the year aTmax in recent years 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, hệ bias coefficient Cs of Hdaymax and aTmax. - Purposes: This research serves for computing and defining Hn,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 sequences Hdaymax, aTmax have the coefficient Cv, the longer the required 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 Hdaymax, aTmax that we need to research, compare and clarify. - Research results at 12 meteorological stations from 1960 - 2010: the highest daily rainfall has the average value `Hdaymax from 89.31 - 237.46 mm, coefficient Cv = 0.24 - 0.55, Cs = 0.34 - 2.99, Cs/Cv = 1.4 - 5.7; the highest rain density in the year aTmax at intervals T = 5mins – 1440mins with the average value `aTmax 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 coefficients Cv, Cs of aTmax , the shorter intervals T are, the smaller they have values and vice versa. 2.3.6. Cycle of large-small-medium changes of Hdaymax and aTmax. - Purposes: This study serves for testing the representation of the period of sampling of the statistical data sequence Hdaymax, aTmax included 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 overall sampling period Hdaymax, aTmax must have the number of years in the heavy rain period and some years in the light rain period in succession. Additionally, researching the cycle of changes also reflects the over-time variation of Hdaymax, aTmax that we need to research compare, and clarify. Figure 2.7: Cycle of changing the biggest daily rainfall in the year Hdaymax at Lang Station – Hanoi City from 1960 – 2010 +/ Time of high values: (1983 - 1994), (2007 - 2010). +/ Time of small values: (1956 - 1983), (1999 -2007). +/ Average time: (1994 - 1999). +/ With 2 cycles. Figure 2.8: Cycle of changing the biggest rain intensity in the year aTmax at the computational interval T = 30 mins at Lang Station-Hanoi from 1960 – 2010 +/ Time of high values: (1996 - 2010). +/ Time of small values: (1986 - 1996). +/ Average time: (1961 - 1986). +/ With 01 cycle. - In order to determine the change cycle of Hdaymax, aTmax , we use the standard error comulative line St = S(Ki – 1) với Ki = (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. - Comments: Hdaymax, aTmax change with cycles; the length of a change cycle of them ranges from 20 to 50 years. In the same station, the change cycle of Hdaymax and aTmax are not the same, at the calculation interval, the 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 stations, Hdaymax and aTmax at T = 5mins – 1440mins reach at least 01 change cycle, even >= 2 change cycles. 2.3.7. Correlation of changes in value and time of together appearance of Hdaymax and aTmax. - Comparing the change in values: using the graph standards to compare the variation coefficient Ki of Hdaymax and aTmax. Figure 2.9: Graph comparing the change in values between Hngàymax and aTmax at the calculation interval T = 5 ® 1440mins at Lang Station-Hanoi from 1960 - 2010 - Comparing the appearance time within the same date in the year of Hdaymax and aTmax: assessed with the color table. Table 2.9: Color table of assessing the duplication in appearance time at the same date in the year of Hdaymax and aTmax from 5 ® 1440mins at Lang Station-Hanoi from 1960-2010 (the same color is the duplication) - Comments: the change in the highest daily rainfall in the year Hdaymax and the parameter of the highest rain interval intensity in the year aTmax in the same station have no the entire duplication, but the difference, 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 between Hdaymax and aTmax depends the calculation interval T: at the calculation intervals, the smaller T is, the higher the difference between aTmax (or HTmax = T.aTmax) and Hdaymax is, the more reduced the difference between aTmax (HTmax) and Hdaymax becomes when calculating the rising interval T, however, up to the value T = 24h, then the interval between a1440phmax (or H24hmax) and Hdaymax does not reach the entire duplication, but 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 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. - Hn,p is now the rain parameter used to calculate Qp 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. - 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 changes in Vietnam to be used in calculating Qp of drainage works on the roads. 3.1.2. Defining the calculated daily rainfall Hn,p under the design frequency p. Lấy mẫu và kiểm định mẫu thống kê lượng mưa ngày lớn nhất năm Hngàymax thu thập thực tế Kiểm tra tính đại biểu: ./ Kiểm tra sai số lấy mẫu ./ Kiểm tra thời kỳ lấy mẫu Tính tần suất kinh nghiệm: ./ Công thức kỳ vọng Xử lý mưa đặc biệt lớn Tìm đường tần suất lý luận phù hợp: ./ Hàm phân bố Kritski - Menkel (K-M) ./ Vẽ tìm đường tần suất lý luận phù hợp theo phương pháp đường thích hợp Kiểm định sự phù hợp của đường tần suất lý luận với tài liệu thực đo: ./ Sử dụng tiêu chuẩn kiểm định Smirnov - Kolmogorov 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 ³ 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. - 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 YT 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 YT,p as the characteristic rain shape coefficient at the period T and the frequency p at any rain zone. (3.9) - 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 YT,p ~ 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 of the curve YT,p ~ T in the frequency p to represent the rain, the moving average is denoted YT, so YT depends only on T, does not depend on p, we have the formula (3.10). (3.10) Với: 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 YT taking the distinctly different rainfall areas, the relationship curve YT ~ T will use different roads relations YT ~ T to partition the rain. The factor YT reflects the shape of the rain: review Figure 1.4 in two rain areas I and II with the same calculated daily rainfall Hn,p , but rain shapes are different, so HT,pI ¹ HT,pII, so it is possible to use the ratio (HT,p / Hn,p) to characterize the shape of the rain and YT = 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 YT. - To determine the Qp small drainage works on standard road TCVN9845: 2013 [5], in addition to determining the parameters Hn,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 YT was used to determine the highest rainfall in periods calculated HT,p at a frequency from Hn,p according to frequency, HT,p = YT.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. - In addition, the characteristic rain shape coefficient YT ~ T is a very important parameter used in the rain zoning. - From the above analysis, the researchers identified factors YT is one of the research content with practical scientific significance. 3.2.3. Results of building the characteristic rain shape coefficient YT 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 YT can be set with very low tolerance under the evaluation criteria of World Meteology Organization (WMO) using the effective criteria Ruseful2 , are reaching the pretty, good levels. - Recommendations for using the characteristic shape rain coefficient ​​YT in the periods T = 5mins® 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. 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. - 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 shape Y T ~ T, ie relations philosophy reduced rainfall intensity calculated according to the duration, the degree of error when calculating the partition between the values ​​( YT,p)k in positions k in the rain than average value YT characteristics for the rain must not exceed the tolerance level, ie to ensure the Ruseful2 ³ [Ruseful2 ]cp , and combined with a 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 Ruseful2 . +) Value [Ruseful2]cp select larger the partition results in as much detail and contrast, values ​​[Ruseful2]cp not less than 40% selected the minimum prescribed level achieved by WMO. + Example on application: partition implemented for Ha Noi with actual rainfall records from 1960 -2010 of 3 stations at Lang, Ha Dong, Son Tay Town with the [Ruseful2 ]cp = 85% , in accordance with the criteria 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 4.2. Determining the calculated rain intensity aT,p based on the calculated daily rainfall Hn,p and characteristic rain shape coefficient YT. (4.3) 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 YT 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 aT,p at the period T and frequency p: - 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 frequency p should apply regression focus methods to find m. 4.3.3. Determining the climate zone coefficients A, B for each rain zone. - From the basic formula, we have: +) 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 every period T, so it is taken the average. 4.3.4. Formular calculating the rain strength Sp and rain shape coefficient m. - 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 missing, not long enough, but knowing the form factor of rain m and rain strength Sp at frequency p. 4.3.5. Công thức tính cường độ mưa tính toán aT,p theo hệ số vùng khí hậu A, B và hệ số hình dạng cơn mưa m. - 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). In which: a is the regression coefficient of the climate zone, depending on the rainy season. 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. (4.15) - 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. - 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. - 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 20’120’. - Formula calculating aT,p under the standard rain strength aTo,p. (4.16) - 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 YT , 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. - Formula determining the calculated rain strength aT,p with interpolation stations in accordance with the calculated daily rainfall Hn,p. (4.17) - Formula determining the calculated rain strength aT,p with interpolation stations in accordance with the rain strength feature Sp. (4.18) 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, 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 T, p : use of norms for effective Ruseful2 and assessment criteria of the WMO. - Evaluation results show that: all of a formula T, p are achieved on Ruseful2 ³ 40%, the minimum level specified ''Passed'' of World 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. CONCLUSIONS AND RECOMMENDATIONS A- The comments and conclusions drawn from research findings and recommendations. 1) Proposing a number of recommendations in the hydrological 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. 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. 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 YT ~ T, ie, strength- rain and rain periods calculated, the tolerance level of the partition ensures rain conditions Ruseful2 ³ [Ruseful2]gh and analysis 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 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 aT, 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 Station-Hanoi. p (%) 1% 4% 10% 20% 50% 99.99% Hn,p (mm) 402.93 299.19 230.10 182.00 122.26 89.20 Other frequency p levels, other meteorological stations in Annex 1. 5) Recommendations for characteristic shape rain coefficient values ​​ YT 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]. 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=YT .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 YT is also used as a criterion to partition the rain. For example: some values YT set in the thesis for Lang Station-Hanoi City: T (ph) 5’ 20’ 60’ 180’ 720’ 1440’ YT 0.087 0.224 0.401 0.577 0.928 1.134 Othe calculation intervals T, other meteorological stations in Annex 2. 6) To recommend the characteristic rain strength values ​​Sp at frequency p = 1® 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 Qp of small drainage works on the roads. For example: some values Sp prepared for the thesis at Lang Station-Hanoi City: p (%) 1% 4% 10% 20% 50% 99.99% Sp 13.27 13.48 13.56 13.74 12.49 1.72 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 Qp of small drainage works on roads. For example: some values m, A, B, a prepared for Lang Station-Hanoi City: Coefficient name m A B a Coefficient value 0.557 4.990 7.197 0.032 Other meteorological stations in Annex 6. 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 = 1® 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: p (%) 1% 4% 10% 20% 50% 99.99% aT0,p at T0 = 20’ 3.33 2.91 2.58 2.31 1.84 0.62 aT0,p at T0 = 60’ 2.11 1.83 1.61 1.42 1.11 0.28 aT0,p at T0 = 180’ 1.15 0.92 0.75 0.63 0.45 0.27 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./.