**Design in H2OMAP Sewer and InfoSewer**

**STEADY STATE DESIGN**

A sanitary sewer collection system has basically two main functions: to convey the designed peak discharge and to transport solids so that deposits are kept to a minimum. It is imperative, therefore, that the sanitary sewer has adequate capacity for the peak flow and that it functions at minimum flows without excessive maintenance and generation of odors. H2OMAP Sewer uses an efficient methodology that allows you to accurately design portions of the sewer network, from a single pipe to the entire system. In this explicit design method each sewer pipe is designed independently without consideration of the flows in other pipes. This can be done because to design a sewer, only the peak discharge is required. The method is attractive because it does not require re-computation of the flow in upstream pipes.

H2OMAP Sewer gives you considerable flexibility to design a new sewer collection system or an existing sewer system.

**EXISTING SYSTEM DESIGN**

Increased sewer flows and/or aging of sewer pipes may call for the design existing sewer systems. H2OMAP Sewer designs existing pipes considering flow capacity constraints while minimizing cost. The model analyzes capacity of existing sewer systems and designs pipes that are transporting flow in excess of the desired capacity.

There are two criteria available for the design capacity calculations:

· Analysis criteria which are used to determine the capacity of existing pipes.

· Design criteria which are used to determine the size of new replacement pipes and new parallel pipes for those pipes observed to have flow depths above their analysis criteria.

H2OMAP Sewer/Pro will determine the optimal replacement and parallel (relief) pipe sizes where pipe capacity is exceeded (i.e., when existing pipes have depth-to-diameter ratios or flow depth-to-channel depth ratios exceeding user specified limits derived from the analysis criteria curve). The design cost for replacing and duplicating (paralleling) a pipe will also be calculated. A different Manning coefficient is then used when designing those pipes exceeding their analysis capacity. The replacement and the duplication channels will have the same shape as the existing channel (i.e., if an existing closed rectangular channel is found to be deficient, the replacement and/or the relief channel will also be a closed rectangular channel).

In addition, H2OMAP Sewer makes sure that flow velocity in the designed pipes meet a user-specified minimum (e.g., not to be less than 2 ft/s to prevent or minimize permanent deposition in the pipes) and maximum (e.g., not to exceed 10 ft/s to prevent the occurrence of scour or other undesirable effects of high velocity flow) design velocities.

**NEW SYSTEM DESIGN**

H2OMAP Sewer can design a new sewer collection system given manhole locations, pipe lengths, sewer loads, topographic data of the sewershed, and design criteria. For new sewer design, the objective is to determine size and slope of a conduit that carries a given flow while maintaining velocity and cover depth within a desired range. The model calculates design flows, which may include both dry weather flows and wet weather flows, and determines pipe size and slope at minimum cost considering various design criteria including depth to diameter ratio, velocity, and cover depth.

The design is carried out for one pipe at a time and it progresses downwards along the flow direction. Trial pipe diameter is assigned to the pipe considering diameter of upstream pipes and a minimum diameter the pipe is allowed to take, and slope is selected considering ground slope, minimum cover required for the location, and a minimum slope allowed for the pipe size. Then flow velocity and flow depth are calculated for the pipe and are compared with the design criteria. If the pipe fails to meet one or more design criteria, pipe slope that satisfies all design criteria for the same pipe size would be searched for. If the pipe fails to meet all design criteria by changing slope alone, the model offers the option to change pipe size to the next large size defined. Drop manhole is used if pipe velocity exceeds the maximum allowed velocity.

A pipe is not allowed to take a diameter less than size of pipes on its upstream end. Crown elevation of a downstream pipe is set to crown elevation of upstream pipe unless the manhole is drop manhole. If more than one pipe is entering a manhole, the downstream pipe takes the lowest of the upstream crown elevations. Drop manholes are used if velocity exceeds the maximum allowed velocity, for example, due to steep terrains. An attempt is made to set cover depths to the minimum to reduce cost of excavation and reinstatement. The following flow chart briefly describes the design procedure.

Design results include pipe diameter, pipe slope, to invert elevation and from invert elevation of pipes, invert elevation of manholes, cover depth at upstream end and downstream ends of a pipe, and cost estimates. Design results could be directly applied to the model database. In addition, the model issues design status information for every pipe indicating whether the pipe is successfully designed or failed. Pipes located to the downstream of a failed pipe will not be designed. Design results could be easily reviewed using pipe profile plot, report, or color coding, for example based on, design status.

A more Step by Step Approach:

1. You can use EPS as the basis of your design **Step 1**

2. In the Design Tab for your existing System pick the Existing System Option **Step 2**

3. You use the existing inverts in your model but you decide on the min and max velocity constraints – the program will only this range of value or Step 3

4. You need a series of d/D tables for your analysis and design or **Step 4** and an example table is shown in Step 5

5. The model run results for the EPS simulation are shown in the Design Output Table, this will tell you the analysis d/D, the design d/D and the new pipe diameters Step 6

**6.** You can also design to parallel pipes or **Step 7**

7. The program also provides costing estimates for the new pipes or parallel pipes **Step 8** but you have to provide another set of d/D tables for the cost

**EXISTING SYSTEM DESIGN**

Increased sewer flows and/or aging of sewer pipes may call for the design existing sewer systems. H2OMAP Sewer designs existing pipes considering flow capacity constraints while minimizing cost. The model analyzes capacity of existing sewer systems and designs pipes that are transporting flow in excess of the desired capacity.

There are two criteria available for the design capacity calculations:

• Analysis criteria which are used to determine the capacity of existing pipes.

**Methodology 4-18H2OMAP Sewer Users Guide**

• Design criteria which are used to determine the size of new replacement pipes and new parallel pipes for those pipes observed to have flow depths above their analysis criteria.

H2OMAP Sewer will determine the optimal replacement and parallel (relief) pipe sizes where pipe capacity is exceeded (i.e., when existing pipes have depth-to-diameter ratios or flow depth-to-channel depth ratios exceeding user specified limits derived from the analysis criteria curve). The design cost for replacing and duplicating (paralleling) a pipe will also be calculated. A different Manning coefficient is then used when designing those pipes exceeding their analysis capacity. The replacement and the duplication channels will have the same shape as the existing channel (i.e., if an existing closed rectangular channel is found to be deficient, the replacement and/or the relief channel will also be a closed rectangular channel).

In addition, H2OMAP Sewer makes sure that flow velocity in the designed pipes meet a user-specified minimum (e.g., not to be less than 2 ft/s to prevent or minimize permanent deposition in the pipes) and maximum (e.g., not to exceed 10 ft/s to prevent the occurrence of scour or other undesirable effects of high velocity flow) design velocities.