Marlborough District Council Roading Assets - Activity Management Plan 2015 - 2018 SECTION 1 EXECUTIVE SUMMARY Under the current level of service specification, all culverts are periodically monitored for condition and serviceability. The monitoring of the drainage facility indicates that while the modern drainage structures are performing well within the limits of age and use, most of the system components which are older than about 20 years are either of inadequate construction or are reaching their end of life. These indications are particularly true of the old county style concrete pipes and the older corrugated galvanised steel pipes. 1.6.3.3 Level of Service The level of service required for drainage facilities is reasonably basic as follows: All drainage facilities shall have adequate capacity for expected discharge (5% Annual Exceedance Probability AEP, or 20yr return period); All drainage facilities shall be operational i.e. no more than 10% of the cross-sectional area the facility obstructed with debris; and All drainage facilities shall be inspected and the status recorded on a regular basis, minimum annually. The current level of service calls for the inspection, monitoring, cleaning and reporting of all culverts and other significant drainage facilities, over the contract period. Where culverts are less than 600mm diameter the present requirement is for any damage to be repaired as a standard routine maintenance activity. Work to larger pipes is categorised differently by the road funding agency and is specifically briefed. Achieving a very high level of proactive maintenance, coupled to a high level of early intervention during inclement weather, appears to be the most beneficial level of service for the drainage facilities. 1.6.3.4 Demand / Growth In the semi-rural and urban areas there is strong and growing expectation from the road neighbours that the road drainage facilities will act as a conduit to remove stormwater from neighbouring locations and will operate to impose some level of control on the impact of stormwater flood events. This expectation is often misguided but not entirely unexpected. As the expectations of neighbours rise, it is anticipated that the council will come under increasing pressure to recognise these concerns. In rural areas on-going changes in land use, i.e. viticulture and dairy conversion, put pressure on drainage systems by changing run off patterns and characteristics. The current level of funding is adequate to address these pressures but there is a risk of more ‘one off’ situations which will put demand on funding. Closer liaison with the Councils Environmental control agencies to ensure adequate conditions are required during the consenting process should mitigate this risk. Potentially the most significant change in demand on the drainage systems is climate change. Over the last 3yrs the frequency of heavy rain events has increased, with at least two significant events each year. The potential for more frequent ‘high intensity’ rain events will put pressure on the capacity of drainage facilities. It is too soon to confirm the weather change with any precision but the situation should be monitored as it will affect future drainage demands. 1.6.3.5 Life Cycle Management 1.6.3.5.1 Surface Water Channel (Kerb and Channel) Maintenance Maintenance, i.e. cleaning activities for formed channels and side drains are incorporated into Council’s NOC 01 contract and the work is funded under work category 113, Routine Drainage Maintenance. Renewal The majority of the kerb and channel asset has been installed progressively from the mid-1960’s and is generally still in good condition. There are some older areas of Blenheim, i.e. Beaver Road, Percy Street area and the Main Street, South Street area where kerbs were installed in the 1920’s and 30’s. This is where the majority of replacements to date have taken place. Kerb and channel generally has a life expectancy of around 80 years with more heavily trafficked streets around 30-40 years. Taking an average life of 70 years and 306km’s of kerb and channel, renewals should theoretically be in the order of 4.3km per year. 30 September 2014 Page 60 of Section