When thinking of building a culvert, some things to consider are:

• offer the advantage of high, weight-loading capacity and low maintenance constructions
• need to be of sufficient size to accommodate a ten year flood (engineering consultants or Environment Bay of Plenty can provide flood calculations)
• must be designed and sited to avoid impeding fish passage
• must be maintained to prevent blockage
• slope embankments 2:1 upstream and 3:1 downstream sides
• can be constructed as permitted activity when applying to the above restrictions unless pipes over
• 900 mm in size are required

Other conditions include:

• there is only one culvert per crossing of the appropriate length
• pipes must be a minimum of 300 mm and maximum of 900 mm
• pipe length should protrude at both ends otherwise a headwall will be necessary
• maximum fill height over the culvert is 1.5 m
• fill batters are stabilised on completion of installation
• culvert is installed on a hard stable bed
• spillways are incorporated into embankment design to prevent the flow going over the top of the structure when blockages occur

• use an excavator for site preparation and placement of pipes to minimise soil disturbance and cost
• stockpile surplus soil well clear of stream channels
• lay culvert pipes on a minimum gradient of 2 degrees (ie 28:1)
• compact backfill around pipes
• the minimum depth fill over the pipes is 800 mm and maximum is 1.5 m otherwise a resource consent is required
• build up embankment with 200 mm soil layers and compact between each layer
• use only clean fill
• sow embankments with suitable ground cover seed immediately after construction to reduce erosion eg grass/legume mix

• use round posts for piles
• drive piles at least 1 m into undisturbed ground
• space piles no further apart than 2.5 m
• tie all piles back to those on the opposite side with cables or wing-wall piles to anchor blocks in the fill slope
• use two clamps for each cable loop
• do not backfill soil directly against wall instead sandbag using a dry mix of sand and cement (4:1) particularly where pipes emerge