derwent forest 3 year holding regime inspection of

Microsoft Word - November Watercourse Inspection Report - REV S0.doc~
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
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
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.
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.
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.
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;
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
Figure 2 – Flamiggs Gill North roof fracture in box culvert section
Figure 3 – Flamiggs Gill North typical deformed sewer cross section
Figure 4 – Flamiggs Gill North broken pipe culvert roof
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:
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.
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.
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.
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.
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.
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.
APPENDIX A
WATERCOURSE PLAN

derwent forest 3 year holding regime inspection of

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