Water Network Analysis

7/31/2019 Water Network Analysis

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WATER NETWORK ANALYSIS

INTRODUCTION

With the increasing tendency of the government organizations to go digital, more

and more information from the government sector are converted to electronic format

everyday. While documents can be typed or scanned directly, complex data formats have

to be processed separately in specialized ways. One of the main areas that is generating

special interest in recent years is the application of "Geographical Information Systems"

(GIS) in local governments. Though GIS can be applied in variety of ways in a

government organization, application of GIS for utility network information is very

interesting. Utility networks usually are of three types, Water, Strom Sewer and Sanitary

Sewer. GIS representation of utility network is usually in the form of a database where

information are stored in classes or tables. One of the popular suit of GIS applications is

from ESRI called ArcGIS. This workshop project aims to produce a GIS Database of

Water and Sanitary sewer network for the City of Rowlett using ESRI's ArcGIS desktop.

The project can be broadly outlined into three parts. First is the preparation of data for

the digitization of the network. This includes cataloging all the AsBuilts that are used as

the basis for the digitization process. Next was the actual digitization process using the

asbuilts as the base. After all the Sanitary Sewer and Water network has been digitized,

next step was the validation of the entire network by building a geometric network. With

the validation of the network, the network is complete and ready for use. In addition to


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the creation of the geometric network, a application for storing and retriving the asbuilts

and another application which uses the water network to map the parcels affected by

closing a water valve was also developed.


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OBJECTIVES

The main objective of this project is to provide a complete water and sanitary

sewer network. The format adopted is the ArcGIS geodatabase model. First is the

creation of the geodatabase by digitizing it using the asbuilt diagrams as base. Once it

has been digitized, the next is to validate the network structure using the network analyst

extension in ArcGIS. This would ensure the integrity of the network and help to cleanup

any loose ends and disconnected features. In addition to this, two applications one for

maintaining asbuilts and another network application which can graphically show the

parcels affected by shutting off of any valves in a water network is to be developed.

Below is the summary of the tasks that are indented to be done by the end of the project.

Water and Sanitary sewer network digitization

Network analysis using Network analyst extension to validate the integrity of

the network.

Hot links from the ArcMap environment to the asbuilt diagrams that thenetwork is based on.

An application using MapObjects in visual basic to retrive and display theasbuilt diagrams.

An application in ArcMap, which will be used to show the parcel layers that,will be affected by shutting off water valves in the ArcMap environment.


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DATA

All the data that is necessary for the creation of the water and sanitary sewer

network were been provided by the City of Rowlett. The data primarily consists of the

following.

AsBuilt diagrams for various subdivisions. Ortho photographs for the City of Rowlett. Road layer shapefile for the City of Rowlett. Parcel layer shapefile for the City of Rowlett. Subdivision layer for the City of Rowlett. City limits shapefile for the City of Rowlett. Regional divisions for the City of Rowlett.

Source and Sink maps.

Asbuilt diagrams are basically civil engineering drawings which show the layout for

the water and sanitary sewer network. They are scale accurate. Asbuilt diagrams are

based on subdivisions. Each subdivision usually has one asbuilt diagram showing the

layout of both the water and sanitary sewer network. But this is not strictly true. Some

subdivisions may have the water and the sanitary sewer diagrams separately.

The second set of data are the high resolution ortho photographs for the City of

Rowlett. The ortho photographs help in giving a detailed overview of the city and the

surrounding and also help in locating features such as water sources and sewer sinks.


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They are also immensely useful in places where ambiguity arises in locating the correct

orientation of the subdivision with respect to the surrounding road information.

The road network is the basis for orienting the asbuilt diagrams on the subdivisions.

Though it is possible to locate the correct subdivision for each asbuilt diagram using the

name attribute from the subdivision's table, the road network provides the correct

orientation. The asbuilt diagrams themselves contain information on the surrounding

roads.

Parcel layer is one of the most important data set used for the database creation.

Though the asbuilt diagrams were based on the subdivisions, the water and sewer lines

themselves in the asbuilt diagrams use the parcels as the guide. This obliviously makes

sense because it is the parcels that are the smallest units that receive water supply.

Subdivisions are units that the asbuilts are based on. They can represent any land

entity as a business development or a housing complex or a place of worship. In addition

to this, the city limit shapefile and the a shapefile dividing the city into twelve regions

purely for project management reasons were also used.

Source and sink maps were provided by the City of Rowlett for locating the water

sources and sanitary sewer sinks.


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METHODOLOGY

Overview:

The general methodology for the project is as follows. First was to create a clean set

catalogue of georeferenced asbuilt diagrams which will form the basis of the water and

sanitary sewer network. Next was the design of the geodatabase. The geodatabase was

designed to accommodate the water and sanitary sewer network in separate geodatasets

with proper projections. Once the datasets were ready, using the georeferenced asbuilts

as the reference in the background, the water and sanitary sewer network was digitized

manually. After the complete network was digitized manually, the network analyst

extension in ArcGIS was used to validate the network.

Geodatabase design:

The GIS database, though not as visible as a GIS map is the backbone of the GIS

data and has to be modeled carefully. The design is based on the intended GIS

application. The obvious first step in the water and sanitary sewer network creation is the

modeling of the geodatabase. The geodatabase is a proprietary ESRI data format for

storing spatial information. A geodatabase is a physical store of geographic information

inside a database management system (DBMS). The main advantages of using a

geodatabase are many. It supports intelligent features, rules, and relationships. The

geodatabase data model supports, a rich collection of objects (rows in a database table)

and features (objects with geometry). Also the geodatabase supports advanced

capabilities such as geometric and logical networks. Vector features can have two, three,


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or four dimensions (x, y, z, and m). The geodatabase was logically divided into water

and sanitary sewer sections. Both were designed as to accommodate spatial features

typical of the water or the sanitary sewer features. Each part was designed as a separate

geodataset. A geodataset is nothing but a fancy folder which contains the physical

representation of the logical elements of GIS data that share the same geographic

coordinate system. In the case of the water network, the geodataset contains features

typical of a water network such as pipes, valves, meters, fire hydrants and water sources.

In case of the sanitary sewer network, the geodataset contains features typical of the

sanitary sewer network such as pipes, manholes, clean outs and lift stations.

The most crucial aspect of the geodataset construction was the coordinate system

selection. The chosen coordinate system was the NAD 1983 State Plane Texas North

Central Zone. This is the common system used for a regional level GIS data work.

In modeling the dataset, the water geodataset was modeled into three separate

feature classes and the sewer dataset was similarly modeled into three separate feature

classes. In the case of water, the feature classes were, water lines, water fittings which

included valves and fire hydrants and water sources. The water lines were line features

and the water fittings and the sources were point features. In the case of the sanitary

sewer network, the feature classes were sewer lines, sewer fittings which included

manholes, lift stations, cleanouts and sinks. As in the case of the water network, the

sewer lines were line features and the sewer fittings and sinks were point features.

Geodatabase has many useful features that facilitate error free data construction.

One these features is the ability to define attribute domains. Attribute domains are used


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to constrain the values allowed in any particular attribute for a table, feature class, or

subtype. Each feature class or table has a set of attribute domains that apply to different

attributes and/or subtypes. These attribute domains can be shared across feature classes

and tables in a geodatabase. This was employed in the construction of the water and

sewer datasets. The following tables show the feature data and their attribute domains.

FEATURE NAME FEATURE TYPEATTRIBUTE DOMAIN

VALUES

Sewer Fittings Point features CO, MH, LS

Sewer Line Line features

4", 6", 8", 10", 12", 15", 18",

21", 24", 30", 36", 12"ABANDONED, 4" F.M., 6"

F.M., 8" F.M., 10" F.M., 12"F.M., 16" F.M., 18" F.M.

Water Fittings Point features M, FH, VALVE

Water Lines Line features 4", 6", 8", 10", 12", 16", 21"


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Georeferencing the asbuilts:

Along with the geodatabase creation, another important step was to georeference the

asbuilt diagrams. The "Georeferencing" toolbar in ArcGIS was used for this purpose.

The asbuilt diagrams were added into the ArcGIS environment with pyramid creation.

This helps in fast rendering of the diagrams itself when repositioned. Using the road

network information in the asbuilt diagram, the diagrams are positioned on their

respective subdivisions. Once the asbuilt diagram is in place, the parcel layer is made

visible and a series of control points are placed on the asbuilt diagram connecting it to the

parcel layer by geographical correctness. The minimum number of control points needed

for georeferencing a asbuilt is three. But the more the number of control points the more

accurate is the georeferencing. The first order polynomial (Affine) transformation is used

for the georeferencing transformation on the asbuilt diagrams. The transformation

functions are based upon the comparison of the coordinates of source and destination

points, the so called control points mentioned above. It was generally easier to catalogue

all the asbuilts into the respective twelve regions and have them organized in in separate

folders.

Another prominent problem was the missing of the asbuilts for a significant number

of subdivisions. This were listed and requested from the City of Rowlett. This asbuilts

were also georeferenced and added to the catalogue.


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ASBUILT DIAGRAM CORRESPONDING SUBDIVISION

Network Digitization:

Once the georeferenced asbuilts are ready, the next step is to digitize the water and

sewer layers. This was done by using the asbuilt diagrams as the basis and using the road

network as the guide. The water digitization usually was done in two parts. First was the

digitization of the water lines then completed by putting all the fittings. In any kind of

network we have a lot of junctions and edges. ArcGIS permits the use of both simple and

complex junctions. In this project the water lines were designed to have only simple

junctions. This necessitates the breaking of the water lines in every place it meets

another water line.

WATER LINES AND FITTINGS SEWER LINES AND FITTINGS


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ArcObjects Application:

The editing method was quiet simple. Either the line or a point feature class was

made the target layer in the editor toolbar and the using the asbuilt diagram as the basis,

the features were drawn on the layer. After each line segment or a point feature was

digitized, the attribute table was opened and the attribute classifying it as a particular line

size or a type of fitting was entered manually. This type of editing was found to be very

very time consuming and needed a lot of patience. So an application using ArcObjects

(the programmable object oriented interface for ArcGIS) was used to create a small tool

that can speed up the editing process. This tool can be used to directly update the

database table from the ArcMap interface without opening the editor updater from the

editor toolbar.


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NETWORK ANALYSIS

Once the digitization is done, the network elements were in place. But the

usefulness of the network to represent the logical utility network is itself is not

guaranteed. The integrity of the network has to be checked to make it logically correct.

This is done by an network analysis. A network analysis is basically check up of the

connectivity of the features that make up the network. A computer algorithm analyses


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the elements that make up the network and validates them against a set of rules they have

to abide by in order to be in a useful network.

The first step in a network analysis is the construction of a logical network by using

the geometric elements that we have digitized. The geometric network is the actual set of

feature classes that make up the network. The logical network is the physical

representation of the network connectivity. Each element in the logical network is

associated with a feature in the geometric network. Geometric networks was built using

ArcCatalog from the simple feature classes that was digitized. In this project all line

features like water mains and sewer mains were modeled as simple edges they were

assumed to be broken at every junction. Some of the rules are shown below in the set of

diagrams.

Sources and Sinks:

The most important elements of a network analysis are the sources and sinks. Any

network has a flow direction which shows the direction of flow of the commodity or

entity that traverses the network. This flow direction in a network is determined by a set

of sources or sinks. For example electricity and water flow are driven by sources and

sinks. Flow is away from sources, such as the power generation station or a pump station,

and toward sinks such as a water treatment plant (in the case of a wastewater network).

Junction features in geometric networks can act as sources or sinks. When you create a

new junction feature class in a network, you can specify whether the features stored in it

can represent sources, sinks, or neither in the network. If you specify that these features

can be sources or sinks, a field called AncillaryRole is added to the feature class to record


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if the feature is a source, sink, or neither a source nor a sink. There were three types of

sources for the water network, Water Tower, Water Booster station and Water station.

For the sewer it was Lift station. But for the network analysis, all the types were treated

as equal.

WATER SOURCE IN ORTHO

PHOTOGRAPHSEWER SINK IN ORTHO PHOTOGRAPH

The approximate locations for the sources and sinks for the City of Rowlett were

provided by the city. Using this approximate location and the road network as a guide,

the ortho photographs revealed the exact location of the sources and sinks. A new feature

class was added into the existing water and sewer datasets to accommodate this sources


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and sinks. In the project, since the exact location of the sources and sinks were not

known, one of the valve fittings or an fire hydrants was assumed to be a source for water

and a manhole the sink in case of a sewer system and the network analysis was

completed. After the exact location of the sources and sinks were found out from the

ortho photographs, the new feature class for the sources and sinks were created and the

network was recreated and then validated again which seem to work fine.

WATER NETWORK SOURCES SEWER NETWORK SINKS WATER TOWER WATER BOOSTER STATION WATER STATION

LIFT STATION METERING STATION

Flow types:


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Once the geometric network is constructed and the sources and sinks are

determined, next is to set the flow direction. This is done by using the set flow direction

in the network analyst extension. Any edge feature like that of an water main or a sewer

main has one of three categories of flow direction. Determinate flow direction,

Indeterminate flow direction and Uninitialized flow direction. Determinate flow direction

for an edge is specified as either with or against the direction in which the feature was

digitized. This is usually determined by the edge features connectivity to the nearest

source or sink. Indeterminate flow in a network occurs when the flow direction cannot be

uniquely determined from the topology of the network, the locations of sources and sinks,

and the enabled or disabled states of the features. Indeterminate flow commonly occurs

for edges that form part of a loop, or closed circuit. It can also occur for an edge whose

flow is determined by multiple sources and sinks, where one source or sink is driving the

flow in one direction through the edge, but another source or sink is driving it in the

opposite direction. For example, an edge that has a source at both of its ends will have

indeterminate flow. Uninitialized flow direction in a network occurs in edges that are

isolated from the sources and sinks in the network. This can happen either if the edge is

not topologically connected through the network to the sources and sinks or if the edge is

only connected to sources and sinks through disabled features. Usually the indeterminate

and the uninitialized flow are the two problem areas that need to be corrected. The

indeterminate flow can be corrected only when we have the information regarding the

direction of flow of each and every segment of the simple edge that participate in the

network. Since the exact information regarding the flow of the edges were not available,

the indeterminate flow was ignored. The only correction that was made regarding the


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network was the uninitialized flow. This was mainly done by checking the connectivity

of the features with each other.

FLOW TYPES IN A NETWORK

Corrections:

After the flow types were identified, as mentioned earlier, the indeterminate flow

was ignored due to lack of information. The uninitialized flow was corrected by

connecting the disconnected ends and resetting the flow directions. Another important

problem that was encountered is the non breaking lines due to faulty digitization. As

mentioned earlier, the network was designed to contain only simple edges. Any edge that


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is not broken and snapped resulted in a uninitialized flow. This was corrected by

breaking up the lines in the appropriate places.

NETWORK APPLICATION

One of the main issues involved in water networks is determining the set of parcels

that are affected by a particular portion of the network. Thus it can be immensely useful

if we can determine which areas will be affected by closing a particular valve in a water

network.

An application for determining the parcel layers that will be closed by turning off a

particular valve was designed by storing the IDs of the valves that supply water to a

parcel in the attribute table of the parcels. Once this valves are chosen and a radio button

is turned off in the ArcGIS application in the ArcMap environment, it will selectively

darken the parcels that are affected by turning off the valve.


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ASBUILT BROWSER

Another application for retrieving the asbuilt diagrams from the hard disc was also

developed. It serves as an simple display tool and helps in retrieval of the asbuilt by

doing a search by name, zooming functions etc.

CONCLUSION

The project aims at building a complete water and sewer network from scratch using

the asbuilt diagrams as guide. The network was validated using the network analyst

extension. The water network contains water lines designated by their sizes and fittings

by their types such as valves or fire hydrants. The sewer network contains the sewer


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mains designated by their sizes and the sewer fittings designated by their types such as

man holes and clean outs. In addition to this, hotlinks from the ArcMap interface were

made to the asbuilt diagrams so that by clicking on any of the subdivision, the respective

asbuilt could be brought up in the default viewer. Other applications included the asbuilt

browser, valve application to show the number of parcels that are affected by closing a

particular valve were developed.

Documents

Water Network Analysis