ABSTRACT
The analysis and implementation of drainage improvements in a built-up area should be based on a comprehensive understanding of the behaviour of the existing drainage system. This understanding is only available through interpretation and analysis of all available information. Information that must be considered includes system record information, flooding and insurance claim information, computer modelling results and public consultation.

KEYWORDS
stormwater management, modelling, public consultation

INTRODUCTION
The City of Regina has been subjected to a number of intense rainfall events which could not be accommodated by the existing storm drainage system. As a result, flooding has occurred in the basements and yards of residential and commercial properties. Street flooding, ponding in low areas and excessive overload runoff have also occurred during these periods. The City has instituted a long range master plan process to review performance of drainage and storm sewer systems throughout the City for the purpose of upgrade and retrofit. The process was developed because of the high number of intense rainfall events which could not be accommodated by the existing storm drainage system.

The main objectives of the long range master plan studies are as follows:

• to investigate the extent of flooding;
• to determine the standards for acceptable service levels;
• to identify areas with substandard drainage;
• to develop upgrading options;
• to undertake a benefit/cost analysis; and
• to recommend upgrading works and work schedule.

Collection and analysis of all available data is regarded as key to successful implementation of these long range master plans.

Background
Master Plan Drainage Area #10 comprises an approximate area of 348 hectares located near City Centre. The area is bounded at the following locations:

• on the west by Albert Street;
• on the south by Wascana Creek;
• on the north by the Canadian Pacific Railway; and
• on the east by Winnipeg Street.

There is a wide range of development within the study area. The northern part is mainly commercial development which contains the downtown core. The commercial area contains older one and two storey buildings with or without basements, high rise office towers and the Cornwall Centre. The central portion is made up of older residential homes and apartment complexes. The southern section is a combination of residential housing, apartments and Wascana Park which includes the Saskatchewan Science Centre and the University of Regina’s College Avenue campus.

INFORMATION COLLECTION


Area Discretization
The drainage areas were broken into four separate drainage areas selected based on the exit point from the study area. The four drainage zones are described as follows:

• Zone 100 - This area is roughly described as the entire area south of College Avenue. The storm sewer in this area discharges to Wascana Creek. Zone 100 is a stand alone area and is not impacted by the rest of the study area.
• Zone 200 - This area is the largest drainage zone within the study area and is located within the area approximately bounded by College Avenue to the south, Victoria Avenue to the north, Albert Street to the west and Toronto Street to the east. The storm sewer in this area discharges into Wascana Creek.
• Zone 500 - This zone basically covers the east portion of the study area and most of the north area also. The approximate boundaries of the area are Winnipeg Street to the east, College Avenue to the south, the railway to the north and a line running north on Toronto Street from College Avenue to Victoria Avenue then west along Victoria Avenue to Broad Street then north on Broad Street to South Railway Avenue. There is a large pocket of land in the Scarth, Hamilton, Rose Street area north of 12 Avenue that is also part of this zone. This area drains to the 7 Avenue Trunk Storm Sewer west of Winnipeg Street.
• Zone 700 - This zone covers the northwest corner of the study area. The approximate boundaries are Albert Street to the west, Victoria Avenue to the south, Scarth Street to the east and Saskatchewan Drive to the north. This area drains to the 7 Avenue Trunk Storm Sewer at Albert Street.

The discretization was performed based on the storm sewer system and the area contributory to the catch basins. The area contributory to the catch basins was derived from City record plans showing surface grading and the field surveys conducted by Associated Engineering as part of this study. The major system drainage scheme was derived from the surface grading elevations. Air photos were utilized to determine the impervious ratios for the individual sub-catchments. The plans of the minor system created from the City’s as-built drawings compared closely with the City’s digital drawing of their trunk storm sewer system.

Surface Depression
To accurately define the topography, a Surface Depression Storage Plan, or more simply, a contour plan of the area was required. The construction of this plan relied heavily upon available information from the City of Regina using as-built drawings containing geodetic elevations on approximately 80% of all catch basin and storm manhole rims, as well as some nearby gutter elevations.

A field survey was conducted to complete those areas lacking sufficient survey information. The survey focused on any catch basin or manhole rims and street or parking lot gutter elevations. This information was added to the base plan to produce a complete contour map of the area.

Storm Sewer System Inspections
As part of the overall system condition assessment an inspection of a portion of the existing storm system was undertaken during the course of the study.

The City of Regina Public Works supplied inspection records from 1991 and 1992 which included information documented in the storm system for one hundred and ten manholes and catch basins within the study area. From these reports, six catch basins and twenty-four manholes were identified to have problems in the past and warranted further inspection.

Thirty manholes and relevant sewers were inspected. These inspections did not note any problems which would affect the hydraulic performance of the sewer system.

Sanitary Sewer Monitoring
A sanitary monitoring program was undertaken during the course of the study to assist in quantifying the degree of infiltration and extraneous flows which enter the sanitary sewer.

For this study infiltration and extraneous flows are described as follows. Infiltration occurs due to the presence of ground water which is able to enter pipes or manholes through structural defects. Extraneous flows are derived from the following three main sources:

• stormwater flows through manhole lids;
• direct cross-connections from storm mains to sanitary mains; and
• service connections on private property via roof leaders and weeping tile connected to storm mains.

Two locations were identified for installation of the monitoring equipment and were based on the hydraulic behaviour of the site and the relative importance of the sanitary main as well as the flooding history of the area.

Public Consultation
A comprehensive public consultation program was initiated to gather information on the existing study area, as well as to inform the public of the study intent.

The consultation program was conducted jointly by The City of Regina’s Municipal Engineering Department and Associated Engineering Ltd.

Associated Engineering undertook the initial task of preparing a questionnaire for property owners within the study area. The questionnaire was designed based on samples from previous studies of this nature. It sought to acquire general information about individual properties such as; the extent of flooding, cost of repairs, physical characteristics, etc. Due to the fact the study area houses both residential homes and businesses, two separate forms were designed. A key aspect in this public questionnaire process was the decision that all returned questionnaires would be entered into a draw to win a $100.00 gift certificate for the Cornwall Centre. The information package was distributed to 60% of the study area, which was approximately 1,940 homes and businesses.

The response rate to the questionnaire was over 28%, consisting of 136 commercial and 419 residential for a total of 555 responses.

The residential statistics indicated several trends:

• Almost 50% of respondents experienced past basement flooding from all sources.
• Very little yard and lane flooding but a larger portion of street ponding was mentioned.
• Half of the respondents have sump pumps in their homes. 68% of the sump pumps discharge to the sanitary sewer systems.
• Weeping tile is present in nearly half of the homes.
• Approximately one-quarter of roof drains discharge into the sewer systems. The remainder discharge into the yards.
• Nearly 40% of homes have yards which slope towards the foundation.
• 25% of the roof leaders discharge onto the ground adjacent to the foundation.

The Commercial questionnaire yielded the following conclusions:

• A large majority of business have basements. About half have experienced past basement flooding.
• 60% of the respondents own sump pumps. 83% discharge to the sanitary sewer systems.
• 60% of roof drains were connected to the storm or sanitary sewers. However, 34% of the respondents to this question were not sure where their roof drain discharges and only 7% of the roof drains discharge to the yard.
• 56% of the respondents indicated they have roof control drains.

Flood Damage Record Analysis. Essentially two sources of information were available to identify and compile flood damage information.

The first source was a summary of flood damage claims for the 1983 storm event which surpassed a 1:100 year storm event. This data was assumed to be related mostly to damaged belongings and property as a result of direct basement flooding.

A second source of flood damage information was obtained through the public questionnaire where property owners were asked to give damage estimates from basement flooding.

From the data comparison of the minor system (see Table 2), it is evident that the occurrence of flooding associated with minor subsystem Zone 700 and 200 is quite low.

Zone 500 had 22% of the lots report past basement flooding. Zone 100 was slightly higher at 27%. Zone 3 has the highest reported number of basements being flooded and represents 62% of all reported basement flooding in the overall study area.

Zones 500 and 100 reported 23% of the lots experienced past surface flooding. However, 60% of the flooded lots in the overall study area are located in Zone 500.

The questionnaire issued to property owners proved to be a valuable resource to identify locations which have experienced past flooding. In addition, the questionnaires also provided physical data which showed a number of factors which may have contributed to flooding and related damages.

Servicing Policies
The City of Regina’s servicing policies for commercial and residential developments have undergone several changes over the years to represent the construction standards in place at the time. The majority of the changes have been concentrated on the discharge location of roof leaders and weeping tile drains.

The combined area is the oldest part of the study area. It was originally constructed with one sewer which collected both sanitary sewage and roof leader runoff from the lots. Subsequent to the original construction, a separate storm sewer was constructed through the area and is generally located in the back alleys. The storm sewer is isolated from the sanitary sewer and collects stormwater runoff from the streets and lots. The original combined sewer now functions as a sanitary sewer except for any roof leaders which remain connected to the system.

Development in Policy Area 1 includes separate storm and sanitary sewers which were typically installed at the same time. However, in most cases combined manholes were installed and cross flow can occur if either sewer becomes sufficiently surcharged.

In addition the City has used different methods to calculate stormwater runoff. Up to 1955 the City used the Rational Method, from 1955 to 1978 the City used an "Improved" Rational Method and since 1978 has switched back to the standard Rational Method as was used prior to 1955. The "Improved" Rational Method was based on average time of concentrations depending on area drained. This had the result of over-sizing the upstream end of a system and under-sizing the downstream end.

Computer Modelling
Computer modelling of the stormwater drainage system was undertaken in order to determine the effects on the system of stormwater runoff and to allow determination of possible remedial works which could lessen the impact of future rainfall events on residents in the area. The modelling was also used to analyse the capacity of the surface drainage system to determine possible improvements.

Computer Model. The OTTSWMM computer model was used during this project as required by the City of Regina. The OTTSWMM model is an adaptation of the US-EPA Stormwater Management Model (SWMM) RUNOFF block.

General Comments on Drainage System. There are a number of storage facilities in place on the minor system. The majority of these storage facilities are ‘superpipes’. Superpipes are pipes in a system which are oversized in relation to the downstream system. These superpipes provide in line storage of flow to reduce the impact on the downstream pipes. Superpipes invariably cause surcharging in the minor system upstream of their location. In general superpipes are only effective for high frequency rainfall and runoff events.

Review of data provided by the City with respect to the 7th Avenue Trunk indicates that this trunk has very low capacity and surcharges under very frequent runoff events. The behaviour of this trunk effects Zone 700 and Zone 500. City staff have remarked that this trunk sewer has a capacity to handle runoff from less than a 1:2 year event. This, in general, means that any drainage system connected to the 7th Avenue Trunk has a true capacity of less than 1:2 years because of the restriction caused by the trunk. This occurs even if the local drainage system has a capacity significantly higher than the capacity of the trunk.

Review of surface grading in the study area indicates no major drainage system is in place or even possible without very significant road reconstruction. The surface grading also indicates very flat lots. The implication is that precipitation, once on the ground, takes a relatively long time to reach the major drainage system, and once in the major drainage system has no where to go if there is no spare capacity in the minor system.

Considering the individual lots the lack of slope is significant. Flow takes place across ground if there is sufficient slope for the flow to occur by gravity or there is sufficient hydraulic head to push the flow across the lot surface. In the case of this study area a major component of the driving force for lot drainage is hydraulic head or depth of water. The offshoot of this is two fold: the depth of water on the lot can cause flooding of the building by entering through windows, doors or cracks in the foundation, and; the depth of water increases the quantity of the water which is absorbed into the ground thereby increasing the load on the weeping tiles and from there on the sewer system. The increased amount of water absorbed into the ground also increases the amount available to enter the sewer system through defects in pipes and manholes.

The lack of a major drainage system also has significant effects on the potential for flooding. Each non-continuous portion of the major drainage system becomes its own ponding area. The depth of the ponding is dependent on how much runoff reaches the area, the geometry of the ponding area, how much can physically be captured by the catch basins and how much can be conveyed in the minor drainage system. The higher the ponding in the major system the higher the depth of flow on the lots must be to force the runoff from the lots to the major system.

As ponding in the major system increases, the potential for increased inflow and infiltration into the domestic system also increases because the domestic system is usually located under the major drainage system. The increased water absorbed into the ground also impacts the domestic system through the weeping tiles, if connected and through infiltration into the house service connection. House service connections are rarely water tight and in some municipalities are a major source of extraneous flows into the domestic system.

System Storage. Existing system storage is in place in Zones 200, 500 and 700. The purpose of these storage facilities is to store flows in excess of the downstream sewer’s ability to convey. The storage system used consists of superpipes. This storage totals 3,233 m³ which is equivalent to just over 1 mm of runoff from the entire drainage area.

Results. The modelling indicates that the existing subsystems have overall stand-alone design return periods of:

	Zone	Return Period
	100	1:5 year
	200	<1:5 year & 1:2 year
	500	<1:2 year
	700	1:5 year

Within each subsystem, individual sections may have greater or lesser capacity than the design return period assigned to the overall subsystem. Zones 500 and 700 drain into the 7th Avenue system which currently has a design return period of less than 1:2 years.

The design return periods as determined in the model are realistic based on the layout and catchment area of each subsystem.

SUMMARY
Analysis of all the information gathered throughout the course of the study allowed a comprehensive understanding of the drainage network.

Based on the minor system statistics, the major system statistics and the modelling results the zone of concern is Zone 500, the Eastern area. This area had 22 % of the lots report flooding from the sewer systems, 23 % of the lots report major system flooding and a storm sewer minor system with a capacity less than 1:2 years.

The information allowed relief scenarios to be tailored for each drainage zone.

Relief Scenarios - West Side Area Zones 200 & 700
This area has the lowest incidence of basement flooding in the study area. The storm sewer system was constructed after the original combined system which now functions as a sanitary sewer. The minor system was determined to have a capacity greater than a 1:2 year storm and less than a 1:5 year storm.

• disconnect catch basins from sanitary system, reconnect to storm
• separate cross connections
• place inserts in all sanitary manhole covers located in depression areas

Relief Scenarios - South Area Zone 100
This area has good topographical relief towards Wascana Lake and only minimal surface ponding occurs. The minor system was determined to have a 1:5 year level of service.

This area has the highest percentage of flooded basements in the study area. This is also Policy Area 2 which has separate storm and sanitary services to each lot. The results of the questionnaire indicate that sanitary sewer backup into the basements is not a problem. Typically the basement flooding was minor and was caused by seepage through cracks in the basement walls, inflow from the tile drains or backup of the storm sewer.

The problems in this area can basically be solved by undertaking improvements to private property including:

• disconnecting roof leaders from the storm sewer and directing flows into the yards away from the house foundation.
• installing a sump pump which discharges water from the weeping tile to the yard.
• capping the storm sewer service.
• regrading the lots to ensure rainwater flows away from the foundation.
• installing a sanitary sewer back flow prevention valve.

Relief Scenarios - Eastern Area Zone 500
It was concluded that the northeastern portion of the study area has the highest incidence of both basement and surface flooding. The minor system has less than a 1:2 year design capacity. This area has the largest depressional storage, has a high number of combined manholes, and connects to the overloaded 7th Avenue Trunk Sewer. All of the above factors are the main contributors to the flooding problem.

A number of potential relief scenarios are available for this area. These scenarios require additional investigation to determine the best relief scenario for this area. The scenarios consist of:

• installation of a gravity storm trunk sewer to Wascana Lake from the centre of Zone 500
• installation of surface detention
• installation of underground detention