Microsoft Word - November Watercourse Inspection Report - REV
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ISSUE: S0 November 2009
Undertaken on behalf of:
Northwest Regional Development Agency
Derwent Forest 3 Year Holding Regime Allerdale Borough Council
Inspection of Culverts and Watercourses
Capita Symonds Issue: Rev S0 CS030885 Date: November 2009
Derwent Forest 3 Year Holding Regime
Inspection of Culverts and Watercourses
DOCUMENT VERIFICATION
S0 Nov 09 Initial Issue TC WS AW
Derwent Forest 3 Year Holding Regime Allerdale Borough Council
Inspection of Culverts and Watercourses
Capita Symonds Issue: Rev S0 CS030885 Date: November 2009
Contents
3. Methodology
......................................................................................................
1
4.2. Summary of Survey Results
..........................................................................
2
4.2.1. Flamiggs Gill North
....................................................................................
3
4.2.2. Flamiggs Gill South
....................................................................................
8
4.2.3. Holdens Gill
...............................................................................................
9
4.2.4. Israel Gill
..................................................................................................
11
4.2.5. Parseys Gill
.............................................................................................
12
5. Conclusions and
Recommendations................................................................
14
Derwent Forest 3 Year Holding Regime Allerdale Borough Council
Inspection of Culverts and Watercourses
Capita Symonds - 1 - Issue: Rev S0 CS030885 Date: November
2009
1. Background
Capita Symonds was instructed by Allerdale Borough Council to
undertake a number of assessments of the Derwent Forest site on
behalf of Allerdale Borough Council, Cumbria County Council and the
Northwest Regional Development Agency (The Clients). The purpose of
the assessments was to determine the extent of the Client’s
liabilities. This report is the output from the ongoing watercourse
inspections based on the original watercourse assessment document
dated March 2009.
2. Purpose of This Report
The purpose of this report is to provide an update of the original
watercourse assessment report and determine the extent of any new
maintenance works required to prevent flooding within or adjacent
to the site. This document has been prepared by Capita Symonds
Limited within the terms of the Contract with the Clients to whom
this document is addressed. Capita Symonds Limited disclaims any
responsibility to the Clients and others in respect of matters
outside the scope of the said contract. No person other than the
Clients, their professional advisors, and Beneficiaries under Deed
of Warranty shall rely on it in any respect and no duty of care
shall be owed to any such third party by Capita Symonds
Limited.
3. Methodology
The assessment was undertaken by: - Walkover survey of the five
main site watercourses and culvert CCTV
surveys of the critical culvert lengths identified in the last
report; - Review of culvert CCTV information; - Report to
Client.
4. Results of Assessment
4.1. Defect Scoring System
A database was previously developed to enable defects to be
recorded and prioritised in accordance with the Client’s
requirements as laid out in the project brief. The five remedial
work priorities are:
1 – Possible minor flooding on site, no flooding off site, only in
a severe storm therefore no action required. 2 – Possible
noticeable flooding on site, minor flooding off site, in a moderate
storm, Low Priority for action. 3 – Possible significant flooding
on site, noticeable flooding off site, in a severe storm, Low
Priority for action. 4 – Possible major flooding on site,
significant flooding off site, in a moderate storm, Medium Priority
for action. 5 – Possible catastrophic flooding on site, major
flooding off site, in any storm, High Priority for action.
Derwent Forest 3 Year Holding Regime Allerdale Borough Council
Inspection of Culverts and Watercourses
Capita Symonds - 2 - Issue: Rev S0 CS030885 Date: November
2009
4.2. Summary of Survey Results
The five main watercourses crossing the site are:
• Flamiggs Gill North
• Flamiggs Gill South
• Holdens Gill
• Israel Gill
• Parseys Gill There are numerous minor tributaries of these
watercourses within the site. However, in accordance with the
brief, these are not included in the survey inspections. The
walkover survey of the site was carried out over four visits during
November 2009 on the 17th, 19th, 23rd and 26th. The weather during
the surveys varied from light rain showers to extreme rain and wind
– the survey visit on the 19th November was aborted due to the
weather conditions. The extent of the watercourses surveyed with
the relevant chainage points are shown on drawing CS030885/CW/017
included as Appendix A to this report. A summary of the current
defects are: Flamiggs Gill North: Chainage 1125 - Priority 1 debris
clearance from culvert; Chainage 1266 - Priority 4 for box culvert
and 450mm pipe repairs. Flamiggs Gill South: No current defects.
Holdens Gill: Chainage 0 - Priority 5 repairs required to secure
site; Chainage 1332 – Priority 1 debris clearance and Priority 2
culvert roof crack repairs; Chainage 1526 – Priority 2 for culvert
fracture repairs. Israel Gill: Chainage 42 – Priority 2 for silt
removal from culvert inlet. Parseys Gill: Chainage 222 – Priority 3
for repairs to culvert.
Derwent Forest 3 Year Holding Regime Allerdale Borough Council
Inspection of Culverts and Watercourses
Capita Symonds - 3 - Issue: Rev S0 CS030885 Date: November
2009
The details of each watercourse along with a summary of the survey
findings and are given below:
4.2.1. Flamiggs Gill North Upstream NGR: 306257 532386 Downstream
NGR: 305076 531013 Length Within Site: 2016m Location : The
watercourse enters the site approximately half way
along the eastern boundary and flows in a south westerly direction
across the full width of the site before crossing the site boundary
in the south western corner.
A description of the watercourse and summary of the survey results
are given below: Chainage 0 to 315 This section of the watercourse
runs through a deep, steep sided, heavily wooded gorge and access
is severely restricted. There are concrete steps from the top of
both banks at the downstream end (chainage 0). The vegetation next
to the steps has been cut back since the last inspection to allow
easier pedestrian access. A trash screen is installed in the
channel where the watercourse passes under the boundary fence.
Since the last inspection this has been cleared and the flows were
passing through even during the extreme conditions on the 19th
November. It was noted that there are still a number of fallen
trees lying within or above the channel in this section. It was
judged that none of these represented a flood risk at this time.
This will continue to be subject to reassessment during future
inspections. Chainage 315 to 963 This length runs in a shallow
channel through a lightly wooded area with no significant access
restrictions. There are two areas where the watercourse is
culverted beneath railway lines or site roads. The first of these
is very short and the condition was visually assessed as still
being ok. The second culvert at chainage 963 is 17m long and has
been checked by a CCTV survey, no defects were found. The culvert
was flowing well during the November inspection. As with the
previous section there were numerous fallen trees noted none of
which were considered to represent flood risks at the time of the
inspection.
Derwent Forest 3 Year Holding Regime Allerdale Borough Council
Inspection of Culverts and Watercourses
Capita Symonds - 4 - Issue: Rev S0 CS030885 Date: November
2009
Chainage 963 to 1125 This length runs in a shallow channel which
deepens towards the upstream end where it outfalls from the culvert
beneath the embankment of the former standard gauge railway. This
entire length of watercourse is heavily overgrown with gorse along
one side and a mature hedge on the other. Access is very limited.
Due to the limited access it was not possible to carry out a
detailed survey of this section of watercourse. However the limited
inspection which was possible did not identify any issues requiring
attention. Chainage 1125 to 1153 This section of the watercourse is
culverted for a length of 26m beneath the embankment of the former
standard gauge railway. A CCTV survey has been completed. Minor
debris in the culvert is blocking about 10% of the culvert cross
section at three locations. However the requirement for remedial
work to repair this defect is Priority 1. The outlet was flowing
well during the visual inspection. Chainage 1153 to 1266 This
length of water course runs through a heavily wooded gorge and
access is limited. At the downstream end of this section there is a
trash screen in the channel which was cleaned after the last
inspection. At the time of this latest inspection this screen was
found to contain some minor debris, however flows were still
discharging into the culvert. Chainage 1266 to 1610 This section of
the watercourse is culverted along the southern edge of the spoil
heap and former Buckhill Colliery areas (an overall length of about
340m). An assessment of the condition of this culvert has been
completed by CCTV survey. The culvert construction is a mixture of
materials and sizes from the outlet upstream as follows: - Circular
450mm diameter clay pipe 82.2 metres length; - Access chamber; -
Circular 600mm diameter concrete pipe 46.2 metres length; - Access
chamber; - Circular 600mm diameter concrete pipe 23.6 metres
length; - Access chamber; - U shaped brick culvert 800mm by 520mm
wide with concrete slab roof
21.9 metres length; - Circular 600mm diameter concrete pipe 36.2
metres length; - Access chamber; - Circular 600mm diameter concrete
pipe 67 metres length. - Access chamber; - Circular 750mm diameter
concrete pipe 37.9 metres length; - Access chamber; - Circular
750mm diameter concrete pipe 24.8 metres length;
Derwent Forest 3 Year Holding Regime Allerdale Borough Council
Inspection of Culverts and Watercourses
Capita Symonds - 5 - Issue: Rev S0 CS030885 Date: November
2009
The brick culvert section has a cracked or fractured roof from
10.8m (from downstream end of brick construction) to 13.4m and also
from 15.3m to 18.9m. The 450mm circular section of culvert is
deformed by about 10% along two 7 metre lengths with the pipe roof
broken at one location. At two locations in the 450mm circular
culvert section there is 25% encrustation on pipe joints. The above
defects in the brick culvert and 450mm clay pipe sections are
Priority 4 for repair (medium priority for action). Rehabilitation
of these defects will be necessary within 3 to 5 years. This
section of watercourse takes drainage upstream of the site. The
following photos show typical details of the Priority 4 repair
locations:
Figure 1 – Flamiggs Gill North roof crack in brick culvert
section
Derwent Forest 3 Year Holding Regime Allerdale Borough Council
Inspection of Culverts and Watercourses
Capita Symonds - 6 - Issue: Rev S0 CS030885 Date: November
2009
Figure 2 – Flamiggs Gill North roof fracture in box culvert
section
Derwent Forest 3 Year Holding Regime Allerdale Borough Council
Inspection of Culverts and Watercourses
Capita Symonds - 7 - Issue: Rev S0 CS030885 Date: November
2009
Figure 3 – Flamiggs Gill North typical deformed sewer cross
section
Figure 4 – Flamiggs Gill North broken pipe culvert roof
Derwent Forest 3 Year Holding Regime Allerdale Borough Council
Inspection of Culverts and Watercourses
Capita Symonds - 8 - Issue: Rev S0 CS030885 Date: November
2009
Figure 5 – Flamiggs Gill North 25% cross section encrustation
Chainage 1610 to 2016 This length of watercourse predominantly runs
in a shallow channel through open grassland. The trash screens at
chainage 1757 and at the site boundary chainage 2016 have been
cleaned since the last inspection.
4.2.2. Flamiggs Gill South Upstream NGR: 306687 531963 Downstream
NGR: 305301 530887 Length Within Site: 1983m Location : The
watercourse enters the site on the eastern side
towards the south eastern corner and flows in a generally westerly
direction across the full width of the site before crossing the
site boundary in the south western corner.
A description of the watercourse and summary of the survey results
are given below:
Derwent Forest 3 Year Holding Regime Allerdale Borough Council
Inspection of Culverts and Watercourses
Capita Symonds - 9 - Issue: Rev S0 CS030885 Date: November
2009
Chainage 0 to 1983 The watercourse runs in a shallow channel
through open grassland across the full width of the site. Where the
watercourse exits the site there is a twin trash screen system
adjacent to the boundary fence. These have been cleaned since the
last inspection and the watercourse was flowing well. Within the
site the watercourse features a number of very short culverted
sections and bridge crossings all of which continue to flow well
despite some debris in the channel. The main site road culvert at
chainage 63 has had the upstream end cleaned since the last
inspection and was flowing well. Where the watercourse enters the
site it is culverted beneath the boundary fence and associated
track. The outlet of the culvert was heavily overgrown and could
not be inspected. However there was no evidence that flows were
being restricted.
4.2.3. Holdens Gill Upstream NGR: 305384 532838 Downstream NGR:
304810 531317 Length Within Site: 2005m Location : The watercourse
appears towards the North Eastern
corner of the site and flows in a south westerly direction across
the full width of the site before leaving the site approximately
half way along the Western boundary.
A description of the watercourse and summary of the survey results
are given below: Chainage 0 to 453 This section of the watercourse
runs through a deep, steep sided, heavily wooded gorge and access
is severely restricted. There are concrete steps from the top of
the gorge on both banks at the downstream end (chainage 0). The
steps to the South East of the boundary fence have had the
overgrown undergrowth cut back, however several of the concrete
steps are sloping and are not considered safe for maintenance
access to the watercourse. It is recommended that these steps are
repaired. Where the watercourse exits the site it is in a formal
channel constructed from concrete blocks with a trash screen
beneath the boundary fence. The gravel has been cleared from the
channel since the last inspection using a Vacta unit.
Derwent Forest 3 Year Holding Regime Allerdale Borough Council
Inspection of Culverts and Watercourses
Capita Symonds - 10 - Issue: Rev S0 CS030885 Date: November
2009
The South East bank of the watercourse at the boundary fence has
washed out to a greater extent since the last inspection report –
additional damage was observed between the 17th and the 26th
November 2009 caused by the severe storm on the 19th November 2009.
The security fence is now compromised and the concrete posts are in
an unsafe condition. Debris has built up next to the collapsing
fence during the recent storm. However it cannot be safely cleared
due to the unstable concrete fence posts. It was noted that there
are additional large fallen trees lying within or above the channel
in this section since the last inspection. It was judged that none
of these represented a flood risk at this time although this will
be subject to reassessment during future inspections. Parseys Gill
discharges into Holdens Gill at chainage 323. Chainage 453 to 487
This section of the watercourse is culverted beneath the site road.
The CCTV survey showed some debris within the culvert, however this
is considered Priority 1 and no action is required. Chainage 487 to
1227 This section of the watercourse runs through a steep sided,
heavily wooded gorge and access is restricted. There are two areas
where the watercourse is culverted beneath former railway lines.
The culverts are approximately 20m long and, due to the limited
access, it was not possible to complete a thorough visual
assessment of their condition or to undertake CCTV surveys. Based
on a visual assessment of flows both upstream and downstream there
was no evidence of restriction and it was assumed that the culverts
were operating satisfactorily. As with the previous section there
were numerous fallen trees noted none of which were considered to
represent flood risks at the time of the inspection. Chainage 1227
to 1526 This length runs in a shallow channel through a mixture of
woodland and open grassland. There are no access restrictions. The
watercourse is culverted beneath the site road at chainage 1332.
The CCTV survey showed Priority 1 debris in the culvert and some
Priority 2 longitudinal cracking in the culvert roof. The cracking
will require long term rehabilitation in 5 to 10 years if the
culvert is required under a future access route. Chainage 1526 to
1648 This section of the watercourse is culverted and a CCTV survey
has been completed. This length of culvert contains numerous
fractures which are considered to require rehabilitation in the
medium term. Culvert repairs in this location are Priority 2 – the
culvert only takes site drainage.
Derwent Forest 3 Year Holding Regime Allerdale Borough Council
Inspection of Culverts and Watercourses
Capita Symonds - 11 - Issue: Rev S0 CS030885 Date: November
2009
Chainage 1648 to 2005 This length of watercourse runs in a shallow
channel through open grassland with no access restrictions. There
are three sections of culvert in this area however these are short
enough to enable visual assessment on site and despite some minor
debris and undergrowth were flowing during the site inspection. Due
to the heavy rainfall conditions during these watercourse surveys
the actual source of Holdens Gill was found to be located further
East than shown on the original watercourse survey plan.
4.2.4. Israel Gill Upstream NGR: 304395 532726 Downstream NGR:
304298 532022 Length Within Site: 811m Location : The watercourse
appears approximately half way along
the northern boundary and flows in a southerly direction before
crossing the site boundary in the vicinity of Camerton
Grange.
A description of the watercourse and summary of the survey results
are given below: Chainage 0 to 42 The watercourse is culverted
beneath the site boundary track at chainage 42. This culvert is
still badly silted upstream of the access road but continues to
flow well at the outlet. Cleaning the inlet will require additional
regarding work upstream and is a Priority 2. Chainage 42 to 632
This length runs in a shallow channel. This entire length of
watercourse is heavily overgrown with gorse on both sides and
access is very limited. Due to the limited access it was not
possible to carry out a detailed survey of this section of
watercourse. However the limited inspection which was possible did
not identify any issues requiring attention. Chainage 632 to 811
This length runs in a shallow channel. This entire length of
watercourse is heavily overgrown and access is very limited. Due to
the limited access it was not possible to carry out a detailed
survey of this section of watercourse. However the limited
inspection which was possible did not identify any issues requiring
attention.
Derwent Forest 3 Year Holding Regime Allerdale Borough Council
Inspection of Culverts and Watercourses
Capita Symonds - 12 - Issue: Rev S0 CS030885 Date: November
2009
4.2.5. Parseys Gill
Upstream NGR: 305300 532554 Downstream NGR: 304941 531561 Length
Within Site: 1588m Location : The watercourse originates towards
the north of the
site and flows in a generally south westerly direction before
discharging into Holden’s Gill.
A description of the watercourse and summary of the survey results
are given below: Chainage 0 to 222 Upstream of the confluence with
Holdens Gill this section of the watercourse runs through a deep,
steep sided, heavily wooded gorge and access is severely
restricted. It was noted that there were a number of fallen trees
lying within or above the channel in this section. It was judged
that none of these represented a flood risk at this time although
this will be subject to reassessment during future inspections.
Chainage 222 to 454 This section of the watercourse is culverted
for a length of 218m. This section of the watercourse has had a
CCTV survey completed. This length of culvert contains numerous
longitudinal fractures/cracks, encrustation and broken sections of
pipe (near outlet) which are considered to require rehabilitation
in the medium term. Culvert repairs in this location are Priority 3
as substantial site flooding of access routes may occur should the
culvert fail. Chainage 454 to 1091 This length runs in a shallow
channel through a heavily wooded area with limited access. There
are six areas where the watercourse is culverted beneath site roads
or railway. Three of the culverted sections are accessible from the
site road and CCTV surveys have been completed for these areas
(chainage 483, 535, 584). No substantial defects were observed. Due
to the location of the remaining three culverts (chainage 727, 943,
997) there is no vehicular access and it was not practical to
undertake CCTV surveys. Based on a visual assessment of flows both
upstream and downstream there was no evidence of restrictions and
it was assumed that these culverts continue to operate
satisfactorily.
Derwent Forest 3 Year Holding Regime Allerdale Borough Council
Inspection of Culverts and Watercourses
Capita Symonds - 13 - Issue: Rev S0 CS030885 Date: November
2009
Trash screens at chainages 547 and 599 have been cleaned since the
last survey. As with previous watercourse sections there were
numerous fallen trees noted none of which were considered to
represent flood risks at the time of the inspection. Chainage 1091
to 1186 This length runs in a shallow channel through open
grassland with no access restrictions. The culverted section at
chainage 1102 continues to flow satisfactorily. Chainage 1186 to
1282 This length runs in a shallow channel and is heavily overgrown
with gorse along both sides therefore access is very limited. The
short culverted section at chainage 1243 was assessed during this
site inspection and is flowing. Due to the limited access it was
not possible to carry out a detailed survey of this section of
watercourse. Chainage 1282 to 1588 This length runs in a shallow
channel and is heavily overgrown with gorse along both sides. No
access was possible and the survey had to be abandoned.
Derwent Forest 3 Year Holding Regime Allerdale Borough Council
Inspection of Culverts and Watercourses
Capita Symonds - 14 - Issue: Rev S0 CS030885 Date: November
2009
5. Conclusions and Recommendations
5.1 Generally the watercourses on the site were found to be
performing satisfactorily
5.2 The previous main defects associated with blocked trash screens
have been repaired since the previous inspection.
5.3 All of the watercourses surveyed included sections which are
culverted. Where access is possible CCTV surveys have been
completed. The culvert that is considered the highest priority for
future maintenance in three to five years is Flamiggs Gill North.
It has some structural defects and it carries water from upstream
of the land controlled by the Client.
5.4 There are a significant number of fallen trees either within,
over or adjacent to the watercourses. This inspection did not
identify any new significant flood risk associated with the fallen
trees.
5.5 Holdens Gill boundary fence at the downstream end of that
watercourse is
now in a dangerous condition. The South East access route steps
require minor repairs and then a temporary fence constructed to
allow controlled removal of the collapsing concrete posts. The
debris in the channel at this location can then be cleared.
Derwent Forest 3 Year Holding Regime Allerdale Borough Council
Inspection of Culverts and Watercourses
Capita Symonds Issue: Rev S0 CS030885 Date: November 2009
APPENDIX A
WATERCOURSE PLAN