1. Underground Systems: Hydraulic Design
CONCRETE APPLICATIONS II
CIMT 305
Underground Systems: Hydraulic Design
1. Drainage Structures
Sanitary Structures
Storm Sewers
Culverts
2. Manning Equation
Nomograph
Roughness Coefficient, n
3.Hydrological Principles
Precipitation
Runoff
Climatic
Topographic
C. Rational Method

2. 1. Drainage Structures Sanitary Sewers
The pipes in a sanitary sewer system must be
Strong and durable to resist the abrasive and
Corrosive properties of the wastewater.
They must also be able to withstand stresses
Caused by soil backfill material
Reinforced Concrete Pipe (RCP) are suitable
For larger sewer systems
RCP is available in diameters up to about 20 ft.
(6m) and in lengths up to 25 ft. (8m)
RCP can suffer from crown corrosion due to
hydrogen sulfide gas

3. 1. Drainage Structures Sanitary Sewers
Manholes are located over the pipe centerline under the following circumstances:
When there is a change in pipe diameter
Change in pipe slope
Change in direction of pipe
At all intersections
At intervals not exceeding 400 ft. (150 m)
Crown Corrosion
H2S
Septic Sewage
Invert
Concrete Pipe

4. 1. Drainage Structures Sanitary Sewer Design
1. Slope of the sewer should follow the slope
of the grade
2. Mannings Nomograph is used to determine the
smallest standard pipe diameter that will carry
the design flow.
3. For that diameter and slope, the velocity is
checked.
4.Once the pipe diameter and slopes have been
established , the invert elevations of the pipe
can be determined and the proposed sewer can
be drawn on the profile

5. 1. Drainage Structures Sanitary Sewer
A 120 –m reach of sewer is to be designed
with a flow capacity of 100 L/s. The street
elevation at the upper manhole is 90.00m and
and at the lower manhole is m,
as shown. Determine an appropriate pipe
diameter and slope for this reach, and establish
the pipe invert elevations at the upper and lower
manholes. Assume a minimum earth cover
of 2m above the crown of the pipe.
Ground

6. Chapter 3 -Hydrology
1. Rainfall
Volume - acre-ft., hectares(ha) (V=Area x depth)
Rainfall intensity - rate at which rain falls
(in/hr. , mm/hr.)
Recurrence Interval (N) years - the average time span between identical storms over a long period of time (i.e. 5 year storm- same as return period)
Probability of occurence (1/N) - is the statistic of occurence in a single year

7. Chapter 3 -Hydrology
2. Surface Water
A. Water Sheds
Drainage Basin - Land which contributes runoff
to a river or stream
Confluence - the point at which two streams converge
Tributary - streams that feed into a first-order stream
Subbasin
Tributary
Drainage
Basin Outlet