With regards to ever increasing development of computer technology, it is time to carry out most of the time consuming calculations with the help of software. In this way men can spend their time on more creative processes and new ways to facilitate life. So HOMA software has been developed by Rayansazeh to achieve the mentioned goal. We hope this software may be useful and adoptable by engineers.
Creating primary input data for wastewater network analysis and design is so time consuming and requires much precision. Processes such as estimating the ground elevation codes, distance to the next manhole, collection area of sewage, population density factors for each area, manholes numbering and following pipes order in data file (Collecting order) are really tedious and can be carried out by this software.
HOMA software is the result of five years continuing work in sewerage networks and computer programming to accelerate the analysis and design of sewerage networks. As today most of the drawings are being done with AUTOCAD® software, we tried to use the facilities of this software for drawing and extracting primary input data.

Sources and References
In developing HOMA software we took advantage of accredited sources and references. As Iranian sewerage consultant companies form the main part of the software customers, we used the “Iran Management & Planning” code and Iranian water industry standards, however the above mentioned codes and standards are themselves prepared by using sources such as “Wastewater Engineering (Metcalf and Eddy)” and “Water Supply & Sewerage (Steel McGhee)”. Thus this software can be used by engineers in other countries.

Introduction
HOMA consists of two main parts, which are:
 

A) HOMA SEWERAGE UTILITY (HSU)
This part of the software is AUTOCAD based and written in “Visual Basic for Application (VBA)”, for drawing network plan and gathering data necessary for hydraulic calculation and also to use the result of calculations to update the network plan.

Some of the abilities of this part:

1) Making a 3D surface by means of elevation codes to extract elevation automatically for each manhole.

2) Considering the slope of each passage or area, user draws a line in direction of the sewer using the line command. Then the software uses these lines for placing pipes and locating manholes and if necessary long pipes will be divided into shorter pipes by specifying Length Breaking Factor. Manholes are numbered in the flow direction (the size of manhole symbol, Arrowhead and text height of the numbers will be adjusted according to user preferences). Then network plan is prepared in DWG format and pipes and manhole numbers will be saved and will be recognized by the program.

3) Identifying the manhole elevation can be done by only a click and the elevation will be read from 3D surface (created before) for each manhole in the network and will be written on drawing and saved in each manhole memory.

After hydraulic calculation is done, this program is able to recognize number and draw longitudinal profile of the longest line then branches and sub branches just by a single click.

Some of the abilities of this part are:
In this program, data inputs are done in four steps and each step of input is an advantage over other programs in the market. However the third step is common between all programs.

I) First step includes six parameters, which are:
1-Equal and Different Manning factor User is able to use Equal or Different Manning factor for Start and End year of design Period .The advantage of using Equal Manning factor is to simplified data input and that of using Different Manning factor is more realistic hydraulic calculation. With no doubt using Different Manning factor for pipes such as concrete which internal roughness changes as time passes, is more realistic.

2-Constant and variable Manning factor:
Manning factor for pipes with respect to sewage flow in them is variable even-though the diameter and material of the pipe would be the same. Most of the software for reaching higher velocity of flow (specially cleaning velocity), without considering the sewage height, takes Manning factor as a constant. Using a variable Manning factor, results in a precise hydraulic calculation. This is a facture in HOMA.

3-Uniform area and variable area:
Usually an area for a pipe has equal value both in first and end year of the design period. But sometimes it is necessary to have a different area for a pipe over years (especially for first manhole of a branch). HOMA can use both cases, depending on the user. Also in HOMA each pipe can accept up to four different areas (different population density).

4- Calculating Kmax by two methods:

K max = 18 + √ p  /  4 + √ p

OR

K max = 5 / p ^ 0.0167

HOMA is capable of using both formulas depending on user preference.

II) Second step includes ten parameters, which are:

1-Water consumption of starting year of project:
This parameter indicates domestic water per capita in Liter per Day for starting year.

2-Water consumption of ending year of project:
This parameter indicates domestic water per capita in Liter per Day for ending year.

3-Water to sewage exchange rate:
Because never all the consumed water becomes sewage, this factor indicates exchange rate.

4- Runoff (liter per capita per day)

5- Operation factor of starting year of project:
Population percent that connects the sewerage network at the start of the project

6- Operation factor of ending year of project:
Population percent that connects the sewerage network at the end of the project

7- Minimum h/D of Sewage in the pipes must not be less than a minimum. However in practice sometimes it is impossible due to limitation in other parts of the program. In HOMA less than minimum of h/D of sewage has been seen especially in starting years and beginning of the sewer.

8- Maximum h/D:
In this part maximum sewage content in the pipe is indicated and capacity of pipe is then considered. In chapter for design procedure this part is dealt with in details.

9-Calculation of infiltration:
Amount of infiltration in HOMA is calculated by four methods for which the user can Choose one to suit the work.
9-1-Per capita
9-2-By Lit/Ha.d, infiltration is calculated according to area covered for each pipe
9-3-By length of sewer
9-4-By length and diameter of pipe

10- Infiltration rate (according to method selected in item 9)

Ill) This step as mentioned before is common in most of software:
After numbering manholes, data in this step is completed as fallow: First, manhole number of the beginning and the end of each part of sewer is mentioned and then elevation code for each of them are introduced, length of sewer, maximum and minimum cover of the pipe, Manning factor (refer to stage 1 and 2), cleaning velocity and maximum velocity and number of areas for each pipe, amount of each area and population density for start and end year of the design period are given.

IV) Step four:
In this step information of the pipes used are given by the user, including: Internal & external diameter and allowed minimum & maximum slope for each diameter. HOMA uses internal diameter in hydraulic calculation and external diameter in calculating depth of pipe erection and excavation. (However the software is capable to consider equal both internal and external diameter)

Design procedure.
In general, design of sewerage network is done on the bases of indicating a pipe with a slope, which is capable passing sewage (that is the capacity of the pipe is larger than flow of sewage) and has a suitable cleaning velocity. Nowadays the second case (cleaning velocity) is less considered in hydraulic design of sewer due to low connection rate into the network at starting years of project, designing tend to become uneconomical. For this case, HOMA design procedure, is based on flow capability (sum of maximum sewage, infiltration and flow) and incase of unsatisfactory capacity of the pipe for transporting sewage, the problem is solved by increasing in slope and then diameter of the pipe. Special attention in this case is given to minimum excavation depth. Meantime for designing all afford is done to keep the limitation introduced by user. Incases where the depth of cover is greater than maximum; this problem is solved by using of Pump or Lift, for which the use of Pump and Lift is with respect to topology.

Sewage velocity in pipe in HOMA never would increase the maximum introduced value by user. In addition with calculation of cleaning velocity, whenever this velocity is less than the given velocity, on the sewer the word Cleaning will be written, indicating artificial cleaning in starting years is necessary.