3 APROACHING AND METHODOLOGY
1.3 DETAILED DESIGN 3.3.1 Road Geometric
3.3.3 Hydrological Anaysis
1.1.1.22 Rainfall Data Analysis
Rainfall data required in hydrological analysis is rainfall data for 10 years of recording or more, in accordance with the standard for calculating flood discharge. The ideal rainfall data is data that is intact and in accordance with what is needed, which in reality is often obtained incomplete data, so it is necessary to fill in the data or estimate the missing data, taking into account the existing rain distribution patterns.
a. Average Rainfall
The maximum daily average rainfall is obtained through the following procedure:
1) Determine the maximum daily rainfall at the rain station in one year, using the Thiessen method to calculate the average daily maximum rainfall.
2) Determine the average maximum daily rainfall (step no. a) in the same year for the other rain stations.
3) Repeat procedure no. a and no. b for each year.
4) From the results of Thiessen's calculations (the result of multiplying the percentage of the area of influence of each station with the daily high rainfall), the highest value is selected in each year.
5) The maximum daily average rainfall data selected for each year is the basis for calculating the design flood.
b. Abnormality Test
The mean value of maximum daily rainfall (in ranking data) must be statistically tested against the maximum and minimum values. The test was carried out using the Iwai method.
c. Frequency Distribution
Frequency distribution / statistics of rainfall using three methods, which are compared with each other distribution,:
1) Gumbel Distribution
2) Distribusi Log Pearson Type III
3) Log Normal Distribution
d. Distribution Conformity Test
The distribution of frequency/statistics of rainfall was tested for vertical and horizontal deviations using the Chi Square Test and the Smirnov Kolmogorov Test
e. Rainfall Intensity
The amount of rainfall intensity is estimated based on the hourly rainfall pattern that occurs. The calculation of the intensity of rainfall per hour is carried out for drainage from the road surface using the Van Breen formula, whereas for flow in rivers or streams with the Mononobe formula.
1.1.1.23 Design Flood Discharge
The design flood discharge is calculated for the flood discharge due to surface runoff on the road corridor and the flood discharge of rivers and creeks that pass on the toll road. The calculation method applied to determine the planned flood discharge is as follows:
f. Rational Method
g. Regional Analysis Method
1.1.1.24 Water Level Analysis
Analysis of water levels in rivers and creeks that cross transversely with the toll road plan is very necessary to determine hydraulic parameters, namely speed, depth, width and bottom slope. The method that can be used to calculate the flow profile in the crossing area of the road plan for high / mountainous areas is the Curved Debit Method (13), this method is used because it is very suitable for non- prismatic channels and will give the best results when used to calculate natural channels.
The water level analysis is carried out by entering various correlations between the water level and the cross-sectional area of the river on the axle of the toll road plan, which will obtain a curve curve for river / tributary discharge that shows various variations in water depth and passing discharge.
The cross-sectional area (A) and the wet perimeter of the river (P), were obtained planimetrically using the Softdesk program, from the Surface results of measurements of the special situation of the cross section of the river / tributary.
With the Trial and Error Regression method on the discharge curve that connects the discharge value (Q) and water level (H), then in the condition of the planned flood discharge (Qren) the flood water level (Hren) will be obtained.
1.1.1.25 Drainage Design a. Side Ditch
The components to be anaylized and calculated : 1) Cross Road Slope
2) Return Period
3) Side Channel Discharge 4) Concentration Time 5) Flow Coefficient 6) Base Slope 7) Side Slope 8) Free board
b. Collector Channel
The collector channel (interceptor) is placed in an excavation or embankment area that is high enough, placed on its banks. The shape of the channel is designed in various shapes, with the most ideal shape being a triangular or semicircular channel. The calculation of the discharge, the slope of the channel, the velocity of the channel flow is planned in accordance with the calculation of the side channel drainage.
c. Median Channel
The median channel (separator) is placed in the super- elevation area. The shape of the channel is designed as an open channel or culvert. The hydraulics concept used is the same as the side channel design concept.
d. Sloping Channel
A chute way is used if the elevation of the culvert outlet has a large enough difference in elevation to the bottom of the channel (especially in the embankment area), the construction of the plunge is analyzed according to the concept of a lined ditch equipped with an energy damper, calculation discharge, channel slope, channel flow velocity are planned in accordance with the side channel drainage calculations.
e. Culvert
The design of culvert that cross the road is categorized into 3 categories according to the elevation of the road compared to the water level from the drainage. If the profile of the drainage water surface is under the road, then a culvert cross building is planned.
If the drainage water surface profile is above the road, then a culvert is designed. And when the drainage water surface profile is parallel to the road, then a siphon is designed.
3.3.4 Geotechnical Calculations