River Management Techniques. Upper Wharfedale Best Practice Project (Information Series No 6)

7.0. Restoring traditional stone pitching and managing existing trees

7.1. Stone pitching

7.1

LOCATION:
Buckden, SD 941774, SD 938773, SD 939774, SD 938772,

LENGTH/AREA: c.35m/87.5m² at traditional pitching sites c.14m/45.5m² on a bend susceptible to damage

DATE UNDERTAKEN:
Autumn 2001

COST:
Varied between £38.00 and £50.00 per square metre

BACKGROUND INFORMATION

On several stretches of the Wharfe the river is confined within a stone-lined bank. Such stone pitching was commonly practised during the 19th century, and is a well tried and tested traditional technique to repair and prevent erosion of river bank and loss of valuable meadowland. It is basically a type of drystone walling, common to the Dales area, where rough stone blocks are used to wall the river bank. The stone is placed by hand and closely jointed without the use of mortar and is a labour-intensive process. This method has stood the test of time and fits more readily into the landscape than does modern hard revetment or engineered blockstone protection. With time, the wall is readily colonised by mosses and liverworts and blends into both the river and the surrounding limestone scene.

DESCRIPTION

Four small sections of damaged existing pitching in the vicinity of Buckden bridge were chosen for rebuilding, two sections above and two sections just downstream of the bridge, one of these being on a sharp bend in the river channel.

DESIGN

A design based on Yorkshire Dales National Park Authority guidelines was used for three of the sites.

On specified sections the existing derelict stone pitching was fully stripped out. This included undercut and damaged sections of wall and bank. On sections where only gapping is required the wall was stripped down to an appropriate secure level.

The footings were prepared and consisted of a row of the largest stones available, laid in a trench 150mm to 300mm deep at the base of the wall. All footings were secured, placed lengthways into the bank and tightly abutted to each other.

The existing stone was used to rebuild the wall. If additional stone was required it was gained from the river bed. All stone used to pitch the face of the wall was placed lengthways into the banking. The batter of the wall tapered evenly to the top or matched the pitched face of the surrounding wall.

Face stones were placed with the following rules in mind:

  • Use the largest stones at the bottom of the wall, grading down to the smallest at the top.
  • Build in even courses (unless the style of the surrounding wall is random).
  • Each gap between the stones should be securely covered by the next course so there are no visible breaks in the wall.
  • The face should be even with no stones protruding.

Through stones were at least double the width of the wall and protruded back into the bank. They were placed at no more than 2m intervals.

Existing tree roots were not disturbed unless they were interfering with the line of the wall. The finished height of the wall matched the existing height of the adjacent wall. The gap between the wall and the bank was packed with smaller irregular stones. Each course was filled and compacted before the next was started. Back-fill for the wall was gained from the river bed.

The top of the wall was built to an even height. After the top layer of fill was used the top of the bank was landscaped with soil. Any loose stone left over from the works was placed at the base of the wall.

The above specification was varied slightly, using additional input from a local contractor and Environment Agency experience, to provide a solution for an area subject to damage from more concentrated river flow on the sharp bend in the river channel. In this instance, large blockstone (about 2 tonnes) was used for the pitching foundations and necessarily placed and trenched into the river bed by a tracked digger vehicle. The vertical pitching work at this site was then capped over and continued with more pitching work in a horizontal plane for about 2m to blend in with adjacent land levels. Birch faggoting was fastened over this with biodegradable rope and covered with topsoil to aid the establishment of a sown native grass seed mix. Provision was made to temporarily bund off revetment foundations with sand bags during work progress to minimise silt disturbance to the river.

ADLib logo Content provided by the Agricultural Document Library
© University of Hertfordshire, 2011