Culvert investigations

Before I start, I’d like to point out that this investigation was conducted by two people – myself and [Howmuch?]. We are both sensible (well, usually) adults and have experience of, and training for, confined spaces. Entering such environments – and storm drains in particular – is a dangerous thing to do. I advise nobody to do it. Water can enter at a moments notice, there can be sudden drops, trips and gas hazards. What we did here, we undertook at our own risk, and in the full knowledge that we were trespassing and could well get into difficulty. Doing so without training, the correct equipment or suitable permission is dangerous, stupid and nobody should do it.

Since this blog started, there’s been a huge interest in Chasewater, and it’s dam. The reservoir was built as Norton Pool in the late 1700’s to feed the canal network. It’s worth thinking about this for a while, as it’s quite a concept, and one often lost on the casual observer. The canal system through the towns of the northern Black Country is almost exclusively fed by the 144m O.D. level of the Wolverhampton canal network, which runs from Horseley Junction, all the way through the suburbs of Worverhampton eastwards to Bloxwich and Brownhills in the form of the Wyrley and Essington canal. There is no canal linked to this that is higher – so where this contour canal transitioned to other waterways, downhill locks were employed. There were 30 alone on the Lichfield and Hatherton, for a start. Then there are locks at Longwood, Aldridge, At Birchills in Walsall, and several complex series at Wolverhapton. Every time a boat uses a lock, water is lost downhill. A busy canal, operating as the freight motorway of it’s day, would see huge water consumption. 

Google Earth aerial imagery with annotations as to the drainage arrangements of the spillway. Click for a larger version.

Water was precious, and Norton Pool was built to feed the canal’s voracious thirst. Over the years, the reservoir has been fed by the Crane Brook from the north (as it always has been), and has seen some water pumped into it from nearby mines. Water also seems to have been recovered from the canal at times when the level was high, and following an enquiry rom fellow Brownhills historian Dave Fellows, Chasewater Wildlife Group head honcho Graham Evans has discussed the nature of the pumping and feed arrangement last year. I’m now fairly sure water was being pumped from the coal mines on Brownhills Common into the Slough Arm. I think a mine owner may even have charged for this supply, although I can’t place where I got that impression. Together with other such sources of what would certainly have been very foul water, these contributed to the general canal supply. When the water was at a high level, it appears to have been pumped back from the canal into the Nine Foot Pool (so called because of the measuring scale erected in it). The Nine Foot is the pool on the Canal side of the dam, at the beginning of the spillway basin, designed to take the flow should the reservoir overflow. The spillway in general seems certainly to be as old as Chasewater itself, although alterations and strengthening seem to have taken place in the late Victorian period.

Ornance Survey mapping of 1902 showing the area in surprising detail. Note the 'Basin' - now dry - is marked full of water, possibly contained by the market sluices.

On Sunday last, after talking about the site for months previously, myself and top local history ferret [Howmuch?] decided to investigate the spillway, and it’s interesting drainage arrangements. To do this, we decided to enter the culverts to see where they went. On the way, we noticed some intriguing things about the civil engineering, and some pointers to the history. Much of this has already been suggested by the wonderful Andy Dennis.

We noted:

• The current state of the spillway basin between Nine-Foot and the old sluice gates is stepped in profile on one side rather than a plain trough shape. We think this may be due to sediment dredging.
• In Google Earth, and on the ground, the land within is darker. We’re thinking this is due to sedimentation from the filthy canal water it would have contained.
• We’re wondering if the canal water was pumped into the basin to settle out before possibly being allowed to flow back into the main body of Norton Pool.
• We have no direct evidence of that, just a hunch.
• The top of the sluice seems to have had lock-style gates. We feel that water probably was retained by them, and they therefore sealed like lock gates.
• The culverts on either side acted as a level control for the basin, but maybe a drain, too, depending on the location of the upper portals which are now buried.
• The new storm drain seems to have been built any time from mid-1960’s to the late 1970’s. It’s a classic Reinforced Concrete Pipe (RCP) design.
• The storm drain runs under the brickwork sluice, under the canal and heath, and emerges on the north of the new bypass as the continuation of the Crane Brook.
• We think it was built to avoid possibly contaminated washdown or runoff  water from the old spillway basin contaminating the then improving canal water.
• The above seems daft but it’s all we can think.
• We’re wondering how it was all constructed, and if anyone has dates or photos. In places the brickwork in the sluice seems to have been disturbed and regrouted.
• The brick sluice is probably now redundant, although in heavy flow conditions I wonder if the basin would backfill as a buffer?

I chose to enter the right hand culvert. About 24″ diameter. Don’t do it kids – it’s messy, uncomfortable and dangerous.

The culvert cuves gently and travels up the slope. The brickwork is in excellent condition. Not a tight fit, but not comfortable.

It seems about 6-8m to the top. As one nears the apex, the channel gets wetter and the debris gets uncomfortable on the belly.

Eventually, there’s a chamber at the peak. I think it’s fairly evident that this held a drop-paddle sluice gate.

On the far side of the gate chamber is a semicircular culvert, too small to enter, the brickwork forming a perfect lip.

Looking upwards to ground level above the chamber. The top is blocked with planks or slabs, and there are guide rails and a control channel for the gate mechanism.

Coming out is a long journey. At the dry section, I turned over and came down on my backside. The air was stale and I was glad to get out.

The upper main sluice gate post. These, we think, were like lock gates and retained a permanent pool in the spillway basin. The portal to the semicircular culvert is somewhere just to the right in the brickwork – the masonry is falling away due to the cavity below.

The culverts are identical both sides. At some point in the last few decades, a storm drain was installed beneath this system. I’m interested in how that was built.

The entrance to the storm drain, below the brick spillway. I only noticed this recently, with the help of an old hand. Made of 5 foot diameter RCP, it’s walkable with care.

The complex and modern canal overflow is part of the ‘new’ system, the overflow itself being slightly to the side of the drain culvert beneath, which is central to the brick sluice, as indicated by access covers.

There’s an access cover at the foot of the brick sluice, central to it. It’s about 2 foot 6 inches diameter and is bolted down securely – presumably to prevent heavy flow from blowing through it.

Similar access covers exist beyond the overflow on the far side of the canal. Someone has been here recently – possibly when the canal was drained to rescuer the dredger.

Back on top, entering the new drain, it’s reasonably airy and dry in the upper area.

After the treacherous downhill of the section under the brick sluice, there’s an access chamber leading to it’s foot.

The tunnel becomes damp and the air stale under the canal, before opening into a very large chamber with a sudden drop. Here, the canal overflow ethers the system from above right. I suspect this is designed to buffer heavy flow. Here, you can hear road noise from the bypass.

Without a rope, I turned back at the overflow chamber – it was a fair drop down and I didn’t want to risk getting stuck.

We found the northern portal – the Crane Brook, effectively – just on the north of the new embankment on the south of the bypass. From here, it winds round the road system before heading toward Stonnall.