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Study on drainage system design

  1. Introduction.

The floods that occur in Oman are considered sudden floods. These floods may cause catastrophic damage to the infrastructure, transportation network, communication lines, water extensions, disruption of traffic during heavy rains, and also cause casualties, The reason is that after extensive analysis, the damage is not only due to the topography of the earth or the changing weather, However, due to urban planning near the wadi rote and the lack of an integrated surface water drainage system in some areas, This is what has become clear in recent years, two cyclones (Gonu) and (Phet), and the damage they caused during the floods.

1.1 Overview.

According to the project that was chosen by the members of this group and the approval of the teacher to study on drainage system design in Sultan Qaboos University Street.

1.2 Project location.

Al-Rusail south direction of Sultan Qaboos Univerity.The exact location of the project is located after the main street exit to the university street leading to the Knowledge Oasis , to Sultan Qaboos Univerity and also to middle east college figure (1) shows the project site location( the effected location), and figure (2) shows the wadi catchment area.

Figure (1) project site location

Figure (2) Wadi catchment area

1.3. Objective.

During flood, the water collected through the Wadi catchment crosses the Irish at University Street with high level flood stream which obstruct the traffic as shpwing in figure (3), through the road until the water is completely discharged from the upstream side of the Wadi route. Our group member decided to select this project to study on drainage system design in Sultan Qaboos University Street, to control the flood flow passing through the box culvert and will be able to regulate the drainage of the flood water through the wadi.

Figure (3)

  1. Hydrological studies.

1.1. Introduction.

Hydrology is defined as the science that studies the properties, quality, location, and motion of water in space Land, on the surface of the Earth or within its outer shells.

This definition of hydrology is described as generic and controversial because it includes parts of other sciences such as (meteorology – oceanography – fluid mechanics) and several other sciences.

For highway designers, what primarily concerns them is the study of the movement of water on the surface of the earth, especially water that passes through transport facilities, and secondly, ensuring internal drainage of this water from the roads, areas between them and intersections.

1.2. Hydrological cycle.

Water everywhere on Earth is one of the most famous basic materials found on Earth, but it is the only one found naturally according to the three substance forms (liquid, solid and gaseous).

The amount of water available varies from place to place and from time to time. Although the wider spread of water is always in the oceans, there is a constant exchange of water between the oceans and the land, and this exchange is called the hydrological cycle.

Figure (4) illustrates the hydrological cycle and explains the movement of water from one stage to another as it moves from one place to another.

Figure (4)

1.3. Rain and runoff.

Based on the hydrological cycle explained in the item (1.2.), Water runoff processes can be defined as a set of related natural processes In which water (rain water) is entered into the water basin and then left as a runoff.

A good understanding of the runoff process is very important, this enables it to be appropriately applied in hydraulic design methods. Therefore, it is necessary to know the important features of the runoff and how it is affected by the different characteristics of the drainage system.

1.4. Introduction to hydraulic design.

Hydraulic facilities include:

  • Open channels.
  • Box culverts.
  • Pump stations.

The hydrological design and analysis of road drainage facilities usually includes one basic general procedure for all drainage cases. Among the basic components of the process of analyzing and designing road drainage facilities are:

  • Data collection.
  • Explore and survey the current characteristics of the area.
  • Guess the future characteristics of the area.
  • Engineering design standards.
  • Estimate the flow.
  • Conditions and requirements for origin and receipt of facilities. 
  1. Literature Review.

In order to properly complete the project, contact was made with the relevant authorities to consider previous studies, to benefit from their practical experiences, to obtain some of the evidence available to them and to review some of their reports.

We would like to inform you that we have contacted several agencies, as follows:

– Meteorological Affairs.

– DG of Meteorological and Air navigation.

– Public Authority for Civil Aviation

– Muscat Municipality.

The data include the amount of rain (mm), rain fall data and catchment area.

As per the information received from Muscat municipality, the expected peak flows at the proposed location are listed in table (1).

Discharge, Q (m3/s) Retum Period, Year
410.7 100
666.4 200
1,215.1 500
1,540.9 Gonu

Table (1)

2.1. Data collection.

In order to fully understand the current situation and enable to simulate water movement during flood time, the project has undertaken a number of data collection excises as follow.

2.2. Wadi catchment area.

By Using map investigated and prepared a map showing the expected catchment area for the wadi through following the ground elevation and its impact on water flow direction. The total catchment covers area of about 150Km2.

  1. Methodology:

The hydrological design and analysis of road water drainage facilities usually includes a basic general procedure One for all discharges. And essential component of the process of analyzing and designing road drainage facilities the express is:

– Data collection.

– Explore and survey the current characteristics of the area.

– Guess the future characteristics of the area.

– Engineering design standards.

– Estimate the flow.

2.1 Data collection, evaluation and documentation.

This topic discusses the general hydrological data collection needs and the location of this data and its analysis Evaluated and documented

The amount of effort required to collect and evaluate data is determined by the importance and size of the project.

Comprehensive, accurate and economical hydrological design requires reliable data for its success. While a failure Design due to insufficient data leads to economic losses and derailment due to downtime its functions.

The structured data collection program leads to effective and successful analysis and design.

The following procedures describe the stages of the data collection process:

A- Determine the type of data required:

– Discharge area characteristics.

– Current use of the region and its future development.

Watercourse line data.-

– Drainage facility site data.

– Climate data for the region.

B- Specify the data source:

– Data from site visit.

– Data from competent departments such as (Meteorological, Ministry of Environment and Climate Affairs).

C- Data evaluation.

2.2 Discharge area characteristics:

A- Space of ​​drainage area:

Knowing the space of ​​the drainage area is important for estimating the amount of (runoff), the area is determined by following

One of the following methods:

– Carrying out direct survey of the area using the traditional methods.

– Using topographic maps of the region, with field validation, to determine presence Natural barriers like ponds.

– Using any other available sources.

B- Topography of the region:

C- Type of soil:

The type or types of soils of the runoff area have significant impact with leakage, leakage prevention and internal water storage or

Assembled on the roof.

D- The plants:

The present and future quantity of plants in the flowing area affects the amount and rate of flow in addition to

Its effect on flow models in and around the drainage facility.

Plant data is obtained by visiting the site.

E- Wadi line data.

Waterways are classified as follows:

– Villager, urban or mixed.

– Clean or unclean.

– Dense or few plants.

– Fast flowing or slow flowing.

2.3. Longitudinal section of the flow line.

The flow line in the longitudinal section should be sufficiently extended from the side of the drainage inlet and from the director’s side to determine the mean slope and control the possibility of any change or deviation in the duct channel. For some codes, it is preferable that this extension distance is not less than 150 meters for both ends (the entrance end and the and terminal exit) if the total length is 300 meters.

2.4. Location of Flow channel.

Note the location of the main channel and any sub-channels, streams or swamps located within a region Cross section of the flow line.

2.5. Cross section.

The cross section represents the dimensions of the water table and contains the expected higher level of water in the table for consideration. For hydraulic calculations, the vertical cross section is taken at the expected direction of the flow line. In some cases, especially in the case of broad flood levels, since one straight cross section is not enough, In this case, a cross-section of a broken line can be made as shown in the figure (5).

Broken line Cross section figure (5)

The number of cross-sections should not be less than four, it is done in the following place:

– At the beginning of the longitudinal section.

– At the end of the drain channel.

– At the beginning of the drain channel.

At the end of the extended longitudinal section.

2.6. Geotechnical information of the site.

A- Soil properties.

Soil reports provide information on site and road soils, and include the following:

– Type of soil.

– Density of soil.

– Depth of each type of soil present at the site.

– Soil properties such as acidity, impurities and specific resistance.

2.7. Hydraulic design of road box culvert.

2.8. Overview on box culverts.

A box culvert is a short hydraulic channel that transfers the flow of a waterway through the road body or any other barrier that obstructs the flow. Box culverts are made from a variety of materials, in different shapes and arrangements. Box culvert selection factors relate to the longitudinal section of the road, the characteristics of the channel, the estimation of the amount of flood damage, the cost of implementing and maintaining the box culvert, and the assumed service life.

2.9. Shapes of box culverts.

There are several shapes of cross sections of box culvert, but the most common shapes are shown in the figure (6), which contains the circular and elliptical box sections and arc tube sections.

The choice of the shape depends on the implementation cost, the boundaries of the water surface level, the height of the road body and hydraulic performance.

Shapes of cross section of box culverts figure (6)

2.10. Materials of box culverts:

The choice of box culvert materials depends on the required structural resistance, Hydraulic roughness, durability, Corrosion resistance and Friction resistance.

The most common materials for building box culverts are:

– Reinforced and non-reinforced concrete.

– Corrugated iron.

– Corrugated aluminum.

Box culvert may be coated with other coating materials to reduce Corrosion and Friction, For example, covering box culvert made of corrugated iron by concrete.

Figure (7) shows a box culvert made of corrugated iron. As the figure (8) shows   Abox culvert made of pre-made concrete.

Box culvert made of corrugated iron figure (7)

Box culvert made of pre-made concrete figure (8)

  1. Result.

Based on our understanding of the available data, analysis and calculation have been prepared to estimate the expected peak flow at the Irish crossing location.

The catchment area data has been collected from Muscat municipality as shown in a table (2), and table (3) shows the box culvert details.

Characteristic of the catchment area
75.1970 Area (hac)
7.51970 Urbanized area (hac)
67.677 Non.Urbanized area (hac)
1.2 Length of the main wadi (Km)
0.0083 Slope of the main wadi (m)

 

Box culvert details
6.10m3/s Target
2.00m width
2.00m Height
0.0083 Slope
80% Filling
3 Number of culvert 


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