Marlborough District Council Roading Assets - Activity Management Plan 2015 - 2018 SECTION 1 EXECUTIVE SUMMARY 1.6.5 Other Structures 1.6.5.1 Physical Description The roading network has a significant quantity of ancillary structures such as retaining walls, cattle stops and concrete fords. In some specific instances there are privately built retaining structures within the legal road. This situation occurs mainly in the steep coastal regions where property owners construct driveways below the public road. The retaining structures fall into four principal types: anchored steel columns supporting horizontal timber laths; steel columns supporting horizontal timber laths (without tie back anchors); rock filled steel mesh baskets (gabions); and dry stacked stone (rip rap). Most of the retaining structures have been constructed in steep terrain to compensate for instability of the road edge due to traffic and storm damage. The most significant groupings of retaining structures are found in the Marlborough Sounds region of the network. Council have recently undertaken to maintain all cattle stops on the road network. Previously many cattle stops were deemed to be the property of the adjoining owner however roading related liability has altered the ability to have private structures on a public road. Records show 137 cattle stop structures are currently within legal road. These structures are located primarily on the Kenepuru roads, the Croiselles - French Pass area roads, the Awatere Valley (where some longer span cattle stops are classified as bridges), Avon Valley, Peggioh, and Rainbow roads. The road asset register contains 28 formal ford crossings of minor waterways. All formal fords are of concrete construction and many of the larger structures have buried pipes to keep the ford crossing dry during normal flows. All the formal fords are subject to overtopping during rain and all the piped versions are subject to pipe blockage due to debris loading during storm flows. The fords on the Rainbow Road are the subject of inundation by gravel and subsequent damage during storms. This road and structures attract 100% funding but typically have a constrained budget. Description Number Length Steel column walls 269 4640 Gabion walls 92 1307 Cattle stops 137 Concrete fords 28 Miscellaneous other 7 Table 6.5.1a: Miscellaneous Structures by Type 1.6.5.2 6.5.2 Age and Current Condition Steel Column Walls The early versions of these walls were constructed with light rail irons without tied back anchors and are typically quite short in length and of limited height. Most are still in good condition but some are exhibiting slippage or rotation. The structures are monitored within the routine structures inspection. When a wall is noted to be performing poorly a repair or replacement is scheduled into the forward works programme. Subsequent versions of this wall type are far more prevalent and typically designed to retain up to 3 metres high over significant lengths using 90 pound rail irons tied back under the road bench by driven or buried anchors. Gabion Walls Gabion walls (steel mesh baskets filled with stacked rock) of varying lengths and heights exist throughout the network. Gabions are typically the most economical method for low to medium height retention. Gabion walls constructed in recent years typically incorporate a sheet mesh anchoring system to prevent rotation. Earlier gabion walls are typically un-anchored and are at higher risk of rotational failure. Gabion walls are considered a flexible retaining wall and as such a degree of settlement over time can be expected which may require maintenance. The galvanized wire used in gabion basket manufacture can have a limited life span, especially in coastal situations. 30 September 2014 Page 77 of Section 1