Flow Diversion Banks: General - Catchments and …

1 Catchments & Creeks Pty LtdV2 February 2010 Page 1 Flow Diversion Banks: General DRAINAGE control TECHNIQUELow Gradient Velocity ControlShort Term Steep GradientChannel LiningMedium-Long Term Outlet ControlSoil TreatmentPermanent[1][1]Flow Diversion banks are not commonly used as permanent drainage 1 Flow Diversion bank down-slope of a future pipeline installationPhoto 2 Flow Diversion bank up-slope ofa building siteKey Principles1. Key design parameters are the effective flow capacity of the structure.

2 And the scourresistance of the embankment The critical operational issue is usually preventing structural damage to the embankment asa result of high velocity flows or construction Flow Diversion banks are often favoured over Catch Drains in areas containing dispersivesubsoil because their construction does not require exposure of the InformationDimensional requirements of flow Diversion banks and berms vary with the type of recommended values are outlined in Table 1 Recommended dimensional requirements of flow Diversion banks/bermsParameterEarth banksCompost berms [1]Sandbag bermsHeight (min)500mm300mm (450mm)N/ATop width (min)500mm [2]100mm (100mm)N/ABase width (min)2500mm [2]600mm (900mm)N/ASide slope (max)2:1 (H:V)1:1 (H:V)N/AHydraulic freeboard150mm (300mm) [3]100mm50mm[1]Values in brackets apply to berms placed across land slopes steeper than 4:1 (H:V).

3 [2]Top width may be reduced in non-critical situations in which overtopping will not cause excessiveerosion and the banks are unlikely to experience damage from construction equipment.[3]A minimum freeboard of 300mm applies to non-vegetated earth embankments. Catchments & Creeks Pty LtdV2 February 2010 Page 2 Free standing earth embankments may be stabilised with rock, vegetation, or erosion ControlBlankets; however, unprotected topsoil embankments are also acceptable for recommended spacing of flow Diversion banks down long continuous slopes isprovided in Table 2.

4 The actual spacing specified for a given site may need to be less than thatpresented in Table 2 if the soils are highly susceptible to erosion , or if intense storm events areexpected ( northern parts of Australia during the wet season).Table 2 Maximum recommended spacing of flow Diversion banks down slopesOpen Earth SlopesVegetated < 10%No maximum2% 12%100m12m4% 15%80m12m6% 20%55m11m8% 25%40m10m10% 30%30m9m12% > 36%Case specificPhoto 3 Flow Diversion berm used tominimise road runoff flowing down a steep.

5 Unstable section of the embankmentPhoto 4 Sandbag flow Diversion bermused to minimise surface flow over arecently seeded embankmentPhoto 5 Earth flow Diversion bank usedto direct runoff towards the entrance of aSlope DrainPhoto 6 Turf-lined flow Diversion bankwith grass-lined outlet chutes at regularintervals along the embankment Catchments & Creeks Pty LtdV2 February 2010 Page 3 Figure 1 Profile of back-push bankThe hydraulic capacity of a flow Diversion bank normally needs to be assessed on a case-by-case basis.

6 However, the associated fact sheets subtitled On earth slope and On grassedslope provide the hydraulic capacity for drains with a standard triangular profile established onearth and grassed slopes geometric properties of triangular drainage channels formed by the construction of a flowdiversion bank are provided in Table 3 Geometric properties of triangular drainage profilesArea (A):ATy= perimeter (P):PTy=+224 Symmetrical or asymmetric V-drain:Hydraulics radius (R):RTyTy=+2422 Area (A):Aaby=+ 22 Wetted perimeter (P):Pyab=+++ ()()1122 Asymmetric V-drain:where flow top width, T = y(a + b)Hydraulics radius (R):Rabyab=++++051122.

7 ()()() Catchments & Creeks Pty LtdV2 February 2010 Page 4 Figure 2 Flow Diversion bank formed from earthPhoto 7 Flow Diversion banks placed each side of drainage line passing through roadconstruction siteTypes of flow Diversion Banks: The following provides a brief description of some of the flow Diversion banks used within ruraland construction land bankA level bank turned up at each end to promote water bankA bank formed by moving in-situ earth up a bankA bank formed by moving in-situ earth down thus forming an excavateddrain up-slope of the bank .

8 Also known as a catch bank . Diversion bankA graded bank used to collect and divert water away from a soildisturbance, or to a dam, drainage channel, or sediment bankA bank constructed with a positive gradient to promote water bankA bank constructed along a contour. Discharge usually occurs at eachend of the bankA bank located along the upper or lower perimeter of a well-defined area,such as a building site, or along the top edge of a bankA bank used to divert water away from unstable used to collect and distribute surface runoff over an increased flowwidth.

9 Typically used on low-gradient, marginal arable land. Catchments & Creeks Pty LtdV2 February 2010 Page 5 DescriptionFlow Diversion banks typically consist of araised earth embankment normally placedalong level or near level ground. Minor flowdiversion berms can also be formed fromtightly packed sandbags, or flow Diversion banks can also beconstructed from tightly packed straw banks are often constructed prior toan impending term perimeter bank is often used todescribe an embankment constructedaround the perimeter of a work are used to either prevent cleanwater entering the site.

10 Or to prevent theuncontrolled release of dirty water from term back-push bank is used todescribe an embankment formed bypushing in-situ soils up a slope to from anearth Diversion banks and berms are usedas temporary drainage systems to: collect sheet runoff (clean or dirty) fromslopes and transport it across the slopeto a stable outlet (Photo 1); divert up-slope runoff around astockpile or soil disturbance (Photo 2); divert stormwater away from anunstable slope (Photos 3 direct water to the inlet of a Chute orSlope Drain (Photos 5 control the depth of ponding around asediment trap such as a stormwaterdrop (field) Diversion banks can also act as a formof topsoil stockpile.))