2020-079 Water Main BreaksDate: September 4, 2020 Report No. 2020-079
INFORMAL STAFF REPORT
TO MAYOR AND CITY COUNCIL
SUBJECT:
Water main breaks and the City’s plan to replace aging water distribution infrastructure.
EXECUTIVE SUMMARY:
Water main breaks occur due to a variety of reasons, but the most common cause is due to seasonal
climate changes described in more detail below. Temperature variations in the north Texas region
have considerably ranges, which indirectly affects underground utility infrastructure. In the last
decade, the average number of water main breaks per year throughout the City was approximately
150. Water main breaks are typically categorized into emergency and non-emergency, and
emergency breaks are repaired immediately after they are reported.
In the last couple of years, the utility department has developed and implemented an Asset
Management System which determines the condition of water distribution pipelines and the
associated risk of future failures (breaks). Based on the assessment of existing water distribution
infrastructure, approximately 26.5 miles (5%) of the total water pipelines in the City have reached
or exceeded their useful life. Given this backlog, staff has implemented an aggressive replacement
program that will replace approximately 8 to 9 miles per year. At this pace, the existing backlog
of aging waterline infrastructure will be eliminated by approximately 2024. After 2024, staff
continue replacing aging water pipelines at a lower rate of approximately 4.5 miles per year to
maintain the water distribution system at acceptable risk levels. While this aggressive replacement
schedule will diminish the number of water main breaks, it should be noted that even after catching
up with the replacement backlog and maintaining the water pipelines at acceptable risk levels water
main breaks will not be completely eliminated.
BACKGROUND:
Why do we have water main breaks? The answer is more complicated than you might think.
Temperature changes are the most common cause of main breaks. Sudden drops in temperature
can freeze the ground, which puts additional pressure on pipes. Hot temperatures also increase
risks; a hot, dry environment can cause the ground to shift, which can warp or otherwise damage
pipes. Many pipes currently in use are made of iron, which can crack during extreme temperature
changes.
In addition to temperature changes, several additional factors can cause a pipe to burst, crack, or
leak, including:
• Corrosion
• Damage caused by shovels, back hoes, or other equipment
Date: September 4, 2020 Report No. 2020-079
• Deterioration due to pipe age
• Nearby construction or pipe repairs
• Opening or closing fire hydrants too quickly
• Soil erosion
• Sudden increases in water volume or pressure.
Large breaks tend to be noticed quickly, either because they saturate the surrounding ground or
cause visible streams of water at the surface of the ground. Small holes or cracks in pipes,
however, can go unnoticed for long periods of time.
DISCUSSION:
In the last decade, the average number of annual water main breaks throughout the City were
approximately 150, with a majority of them occurred during the summer season. Given that large
temperature variations are very common in northern Texas, which is a major cause for water
main breaks, main breaks cannot be completely eliminated. However, by addressing other
(secondary) factors we can reduce the number of breaks. Staff is diligently working on
eliminating/reducing these secondary factors, which includes replacement of aging
infrastructure. The graph below shows the annual number of water main breaks since 1986. As
seen in the graph, City staff has consistently worked on reducing the number of water main
breaks annually by reducing secondary factors, including a focused program for replacing aging
infrastructure.
Main Break Repairs
0
50
100
150
200
250
300
350
400
450
500
'86'87'88'89'90'91'92'93'94'95'96'97'98'99'00'01'02'03'04'05'06'07'08'09'10'11'12'13'14'15'16'17'18'19'20 FYTDMain Breaks
Date: September 4, 2020 Report No. 2020-079
Repairing a water main break may require water to be shut off for an extended period of time,
which is inconvenient for customers. If possible, water is allowed to continue flowing during the
repair, although the ability to continue service depends on water pressure and the extent of the
damage. When a water main break is reported, City staff typically follow the steps listed below:
• After reaching the location of the reported leak, staff conducts visual inspections to
determine the amount of water leaking, reviews accessibility of the site, assesses the
water damage, and identifies other safety concerns. Based on field observation, staff
determines the severity of the water main break and determines if it is an emergency
repair that must be completed immediately (even during non-working hours,
evening/nights or weekends) or if the repair can be postponed until normal business
hours.
• Once a water main break is identified as an emergency repair, the crew and equipment
are dispatched to the break location.
• Emergency Line Locates (Texas 811) are requested, which typically takes 2 hours.
• Once line locates are completed, staff turns the water valves (partially or fully off) to
reduce or shut down water flow in the damaged main.
• The area is then excavated to expose the water main.
• The water main break is located and repaired, typically by using a clamp for smaller
cracks/holes and full replacement if the damage is extensive.
• After the repair is completed, the excavated hole is backfilled, compacted and restored
back to its previous state.
Water Infrastructure Risk Assessment
The City of Denton is one of the oldest Cities in the metroplex and has aging utility (water and
wastewater) infrastructure. In order to maintain an inventory of existing infrastructure and to
identify future failures, staff has collected extensive data on the water distribution infrastructure.
Additionally, in the last couple of years, the water department has developed and implemented an
Asset Management System which assesses each water distribution pipeline and determines the
condition and the associated risk of future failures. A ‘condition’ and ‘criticality’ scoring chart
used in the City’s Asset Management System is shown below. The risk assessment is based on the
following attributes;
• Pipe Material
• Age of Pipe
• Number of main breaks
• Soil Characteristics
• Customers served
• Access Issues
• Pipe Resiliency
Date: September 4, 2020 Report No. 2020-079
The existing water infrastructure consists of approximately 635 miles of transmission and
distribution lines throughout the City. As the City continues to grow with the addition of new
development (both residential and commercial), it adds approximately 5 to 6 miles of water lines
annually to the existing infrastructure. Based on the risk assessment of the existing water
infrastructure, approximately 26.5 miles (5%) of the total water distribution infrastructure has
reached or exceeded its useful life.
-35%
-30%
-25%
-20%
-15%
-10%
-5%
0%
5%
10%
15%
20%
25%
30%
35%
2020 2025 2030 2035 2040 2045 2050 2055 2060 2065 2070Percent of Total LengthWater Distribution Useful Life Curves
Lowest Financial Burden 8,000 ft/yr (Reduction)16,000 ft/yr (current)
24,000 ft/yr 1% Replacement Rate 1.5% Replacement RateSunkenCapital InvestmentCostof Emergency Repairs
Date: September 4, 2020 Report No. 2020-079
Replacement Plan
In the last couple of years the City staff has developed a replacement program that not only
identifies the backlog of aging infrastructure replacement needs but also estimates an annual water
pipeline replacement rate which will help maintain the infrastructure at acceptable levels for the
next 20 years. As shown in the graph above, it will require approximately 8 years to catch up with
the backlog of aging waterlines if staff replaces existing lines at a rate of approximately 4.5 miles
(24,000 linear feet) per year (intersection of orange line and 0% percent of total length on the
above graph).
In order reduce the number of years required to
eliminate the existing backlog of aging
waterline replacement needs staff has
augmented its in-house maintenance crews with
external contractors. The City’s in-house crews
replace approximately 2.5 to 3 miles (14,000 to
16,000 linear feet) of aging water pipelines per
year. The last fiscal year (FY19-20), by
outsourcing (contractors) the replacement of
water distribution lines the City was able to
replace an additional 5.6 miles (29,691 linear
feet) for a total replacement of 8.4 miles (44,313
linear feet). Staff intends to meet similar targets
for next fiscal year starting October 1, 2020. With the new replacement targets of approximately
8 to 9 miles per year the existing backlog of aging waterline infrastructure should be eliminated
by approximately 2024. After 2024, staff will have to continue replacing aging water pipelines at
a lower rate of approximately 4.5 miles per year to maintain the water distribution system at
acceptable levels.
STAFF CONTACT:
Pritam Deshmukh, P.E.
Deputy Director Water/Wastewater Utilities
(940) 349-7710
pritam.deshmukh@cityofdenton.com