small stream erosion repair · 2013. 5. 7. · best practice guide version # 1 – april 2013 small...

BEST PRACTICE GUIDE VERSION # 1 – APRIL 2013

SMALL STREAM EROSION REPAIR

Details contained in this document have been prepared to offer assistance to rural landowners, GWRC staff and Contractors. The techniques and plans contained in this Guide have been prepared and included on the basis of the information accumulated by GWRC and the experience of GWRC staff over many years in undertaking and supervising repair work. This is made available to offer assistance to rural landowners who experience erosion and are considering whether or not to undertake repairs. The guidelines and plans have been compiled to deal with common or standard situations. Landowners are cautioned against using the guidelines and plans in circumstances which may not be common or standard and are advised to seek professional assistance if in doubt or where there has been significant erosion. While GWRC has endeavoured to ensure the guidelines and plans are a fair statement of the best practice derived from experience, it cannot assume responsibility to any third party for the reliability, accuracy or completeness of the information or plans contained in this Guide or of the applicability of either to any particular circumstances. In areas of significant erosion, detailed engineering investigation / design may be required.

COVERSHEET Drawings included within :

• Typical Erosion Scenario Dwg Ref : RL-5317/01

• Willows Driven in at Toe of Bank Dwg Ref : RL-5317/02

• Re-establish Former Channel and Plant Willows Dwg Ref : RL-5317/03

• Taper Back Erosion Face and Plant Willows Dwg Ref : RL-5317/04

• Riparian Strip alongside Stream Dwg Ref : RL-5317/05

• Shift Channel and Construct Tethered Willows Dwg Ref : RL-5317/06

• Tethering (Cabled Willows) Dwg Ref : RL-5317/07

• Tree Groynes (Trenching Willows) Dwg Ref : RL-5317/08

• Hard Edge Works (Concrete Block or Gabion Groynes) Dwg Ref : RL-5317/09

• Pile & Fascine Revetment Protection Dwg Ref : RL-5317/10

• Stock Fence across Small Stream Dwg Ref : RL-5317/11

For latest version of guide, contact Greater Wellington Regional Council Flood Protection Department

For more information, contact Greater Wellington:

PO Box 11646 Manners Street

Wellington, 6141 T 04 384 5708 F 04 385 6960

April 2013

File N//50/03/07 v1

e-doc #1178298

www.gw.govt.nz [email protected]

Erosion face

00. yit 9./4 Igt it It

i

CROSS SECTION - (Existing situation) N.T.S.

Former channel

Gravel beach

Slumping \

Former channel

New eroded channel

CROSS SECTION - (Situation following erosion) N.T.S.

Eroded Face

PLAN - (Situation following erosion) N.T.S.

EROSION STARTS

• In a flood the stream has greater turbulence and increased energy. Pieces of bank get carried away causing erosion to stream banks and stream bed.

• As the volumes and velocities of water increases the stream bed mobilizes and gravel is transported down the stream.

• At the erosion site the channel is now wider. As water velocities naturally slow on the inside of a bend gravel begins to deposit.

• A gravel beach builds up opposite the erosion site, narrowing and squeezing the stream channel and increasing velocities which encourages further bank erosion.

• As the Stream channel is now narrower, a scour hole has formed exposing raw bank now at risk of collapse from constant erosion and excavation by the next flood.

PREVENTING FURTHER EROSION

A variety of methods can be used to try and prevent further erosion.

Some of these methods have been outlined in this drawing series RL-5317 (Standard Details - River / Small Stream Erosion Repair) by Greater Wellington's Flood Protection Department.

The methods attempt to stabilize the stream by addressing one or more of the issues outlined in the bullet points to the left.

DESIGN

greater WELLINGTON REGIONAL COUNCIL

Te Pane IVIatua Taiao

EROSION REPAIR SMALL STREAM

STANDARD DETAIL TYPICAL CHANNEL MOVEMENT / EROSION SCENARIO

VERSION # 1

COMPILED April 2013 DRAWN P.COOK April 2013 CHECKED c. e APPROVED —ee:c.--.41-ief 6151/3 Drawing No. RL-5317 / 01 FILE N/50/2/6 Cad: RL-5317_C.dwg

1.11.1..■1 =MINIM=

Former channel

0 New eroded 0 channel 0

0 00 0 0

PLAN N.T.S.

Willow poles planted at toe of eroded bank

.00

■■■••°1

Toe of bank

Reformed channel CROSS SECTION N.T.S.

Willow poles driven into toe of bank at lm centres. Plan to have the majority of the pole buried with approx. 300mm protruding.

Erosion face

co 2

Remove build up of

E

.......-....Alt

E , .. 40,,,,t,-;,..1"---:-..-.■,--7.---...

••• "----...W1.0 4W--iiii;', gravel Gravel beach

CD .14 " ' 1 ..-S. .j1 "., ni if Al 111-'10 .4 in 1 r • _C'f, _

4.■•••■ 40r..... JO Abw -Now "Wier dr. -

0

4.164111r2 ailyw

'.4.15.... ....... di,

DISCLAIMER:

GWRC and other agencies involved in the preparation of this plan assume no responsibility as to the reliability, accuracy or completeness of the information shown or for any interpretation or action taken by any agency or individual in relation to information provided on this plan.

This plan has been prepared to offer assistance to rural landowners, the landowner is under no obligation to carry out these works. In areas of significant erosion, detailed engineering design / investigation may be required.

The landowner will need to contact the necessary authorities and service providers for building consent /resource consent (if applicable) prior to any work being carried out. Please note there is always a risk of works being outflanked or destroyed in a flood.

See also caution on cover sheet

OBJECTIVE

To use willows to secure the eroding bank edge and willow foliage to protect the upper Erosion face from flood velocities. Regular removal of gravel build up on the beach opposite is required to lower the pressure on the willows.

MATERIALS

Use cut poles of a multi-stemmed Osier willow e.g. Salix Purpurea 'Booth'. Poles should be 50mm 0 Min. Plan to have the majority of the pole buried with 300mm approx. protruding. Use a heavy steel bar to prepare a hole if possible, then drive in the willow pole. Plant poles at lm spacing.

LIKELIHOOD OF SUCCESS

Initially low until willows establish an effective root system. This could take up to 4 - 5 years in difficult soils.

Perseverance, timely maintenance and no floods during establishment may assist with success.

NOTES:

Not appropriate where significant assets are at risk. Not practical if scour hole is too deep. Not practical in large gravels. Must be protected from grazing stock. Vulnerable to abrasion damage in floods.

PLANTING WILLOW POLES

Poles should be cut from modern sterile hybrid stock. If poles are purchased the seller should certify source and breeding. Sterile hybrid willows have been specially developed for river protection work with extensive root systems, quick growth and large girths while limiting seeding, brittleness and wild strike.

The preferred osier willow is Salix Matsudana x Salix alba sterile hybrid "Moutere". These willows reach up to 6m in 2yrs or > 20m on maturity.

Willow poles should be collected and planted when the tree is dormant (June - July). To ensure success the poles should be planted immediately after collection. If kept moist, poles will remain viable for a considerable time.

Hand planting in gravel should be assisted by an excavator or bulldozer with a ripping tyne or a tractor with a motorized auger.

To guarantee success poles must be planted deep enough to ensure their root system has access to moisture all year round. This means plant as deep as practical.

In silty soils it is often possible to drive poles in by hand. A heavy steel bar is useful to prepare a hole. Often a fence post hand driver can be use to drive large poles. An end cap can be made from a length of suitable steel tube. This is slid over the poles and then the pole driven in with a heavy hammer. Allow to cut the damaged top off the pole with a chain saw.

An excavator can sometimes be used to push poles into place.

DESIGN DRAWN

COMPILED P.COOK

VERSION # 1 EROSION REPAIR April 2013

April 2013


Te Pane Matua Taiao

SMALL STREAM STANDARD DETAIL

WILLOWS DRIVEN IN AT TOE OF BANK

e cp/AKileJ Sisit APPROVED ..--(--4-4et 6

Drawing No. RL-5317 / 02 FILE N/50/2/6 Cad: RL-5317_C.dwg

CHECKED

DISCLAIMER:



The landowner will need to contact the necessary authorities and service providers for building consent/resource consent (if applicable) prior to any work being carried out. Please note there is always a risk of works being outflanked or destroyed in a flood.

See also caution on cover sheet.

■■■■

Former channel

Erosion bay filled with gravel and planted willows.

PLAN N.T.S.

Plant 50mm 0 x 1.5m long willow poles lm deep @ 1.5m centres

Gravel removed from beach to fill eroded channel

z Former eroded channel / scour hole

\z

Erosion face , aat Paw

11.1 .10, ,r,eit, 111111.7,N,Nor... Fill eroded channel FAVa. 404 e, with gravel from -.1.11,■*2

beach opposite ■S-1 AVZ-r. -M1211P4.

ao,-".■■■ •■■• /14 dor.—

Fill eroded channel with

OBJECTIVE gravel from beach opposite CROSS SECTION N.T.S.

Reformed channel

To reduce the risk of further damage by shifting the channel off the Erosion face and planting willow poles to prevent the channel returning

MATERIALS

Use cut poles of a multi-stemmed Osier willow e.g. Salix Purpurea 'Booth' . Poles should be 50mm 0 Min. x 1.5m long.

METHOD

Use an excavator to shift the channel off the erosion by using gravels from the beach opposite. Plant poles lm in and 0.5m out @ 1.5m centres in shifted gravel as work proceeds. Alternatively push poles into loose gravels with digger bucket.

If the worked gravels are silty, establishing a grass cover may help with protection.


Reasonable, provided damage is repaired quickly. Losses are likely in the initial years as the willows establish (up to 3 - 5 years). The loose gravel is also vulnerable to further erosion in a flood

Note :

Not appropriate where significant assets are at risk. Must be protected from grazing stock.









DESIGN DRAWN

VERSION # 1 EROSION REPAIR COMPILED

P.COOK _April 2013 April 2013


Te Pane Matua Taiao


RE-ESTABLISH Former channel and PLANT WILLOWS

CHECKED APPROVED

Drawing No. RL-5317 / 03 FIE N/50/2/6 Cad: RL-5317_C.dwg

c,se, Ott4AP4

(45,112

Plant 50mm 0 x 1.5m long willow poles 1 m deep @ 1.5m centres. First row placed at water level

\— Erosion face

Former eroded channel / scour hole

Cut the Erosion face back to a stable slope.

DISCLAIMER:


This plan has been prepared to offer assistance to rural landowners, the landowner is under no obligation to carry out these works. In areas of significant erosion, detailed engineering design /investigation may be required.



FILE N/50/2/6 Cad: RL-5317_C.dwg Drawing No. RL-5317 / 04

CROSS SECTION N.T.S.

OBJECTIVE

To reduce the risk of further erosion by increasing the waterway width and thereby lowering velocities. To improve stability at the site by taking the Erosion face back to a more suitable slope and planting willows

MATERIALS

Use cut poles of a multi-stemmed Osier willow e.g. Salix Purpurea 'Booth'. Poles should be 50mm 0 Min. x 1.5m long.

METHOD

Use an excavator to cut the eroded face back to a stable slope. Plant poles lm in and 0.5m out @ 1.5m centres. in the cut face with first row at the waterline.


Reasonable. Increases with time as willows establish (up to 3 -5 years) but perseverance, timely maintenance and few floods will increase success.

Note :

Not appropriate where significant assets are at risk. Must be protected from grazing stock.









EROSION REPAIR greater WELLINGTON

REGIONAL COUNCIL

Te Pane Matua Taiao


TAPER BACK Erosion face and PLANT WILLOWS

Open pasture

la!‘ '41,1 414 IP 1, T: b. al Sit tie ' I

Eroding bank

Slumpin

Former channel Gravel beaches

DISCLAIMER:

EXISTING PROFILE (Showing erosion)

N.T.S.

15 - 20m Riparian Strip alongside stream (interplanted with natives)

Rear trees thinned and topped as appropriate to rejuvenate and promote establishment of native species

Salix Matsudana 'Moutere' at 2.5m spacing

Front edge trees layered as appropriate to thicken protection




See also caution on cover sheet

Fencing where appropriate


Beach metal bladed against willows in the initial years as required to protect and promote establishment

.,..0

_gefire," I 41Piiiloii-i■-, -4"-,s04.— ', 111-41.--,411.. ... _____ .... .... ....■ .....1,..- r m dozt..7

;0.4.......e .....p.74, _ ..,..,,..*.orz,--.....0. / -,...... -,, ....___ ..."0,,,,,r,

4-514 40411111EIN, -411 ......,,....47.141r.r...,„.....4.x....■ 4.4y,":".i.. .710

is -50-.4-4).%,...e.",„,....1c---,..., ..-7:.■ -isal--...... .. 4,..: PROPOSED PROFILE

N.T.S.

Fencing to control stock

Reformed channel









DESIGN COMPILED VERSION # 1

.05e,--4ZW 6ig )1? Drawing No. RL-5317 / 05


APPROVED STANDARD DETAIL RIPARIAN STRIP ALONGSIDE STREAM

Te Pane Matua Taiao FIE N/50/2/6 Cad: RL-5317_C.dwg

Optional wire rope looped around willows and tied to anchors

Alternative driven anchor

Tethered willows. Cover with gravel, sticking out. Cabled together as shown, anchored every 5 - 10m (depending on willow size)

Gravel removed from beach to fill eroded channel Erosion face

go.

1-.4tP6r,

:Op sit. 41164.

4. go . • .4Arrott —

Aik

Reformed channel Wire rope

Wire rope

Concrete block anchor (optional)

Concrete block anchor


OBJECTIVE

To reduce the risk of further erosion by shifting the channel off the erosion and construct a barrier of live willows. The bundled willows provide a physical barrier (which increases as they grow) against stream velocities.


DISCLAIMER:


This plan has been prepared to offer assistance to rural landowners, the landowner is under no obligation to cany out these works. In areas of significant erosion, detailed engineering design / investigation may be required.



DETAIL N.T.S.

MATERIALS

Use large branches of tree willows (Matsuda or similar preferred) Heavy wire rope. Concrete blocks or Rail irons as anchors.

METHOD

Use an excavator to shift the channel off the erosion. Excavate a trench and place large willow branches in a bundle in the trench. Place on a slope with their butts in the water and their branches up (refer to diagram top of page). Tie down securely with wire rope to the anchors (either concrete blocks or driven Rail irons). Use excavator to throw gravel over the willows so they are covered -31 out


Good provided they stay well secured and any maintenance is carried out promptly.

NOTES:

Must be protected from grazing stock. Not appropriate where significant assets are at risk.









VERSION # 1

DESIGN DRAWN EROSION REPAIR COMPILED

P.COOK April 2013 April 2013

CHECKED greater WELLINGTON REGIONAL COUNCIL

Te Pane Matua Taiao


SHIFT CHANNEL and CONSTRUCT TETHERED WILLOWS

C. C. 44,14/1A1

APPROVED Drawing No. RL-5317 / 06 FILE N/50/2/6 Cad: RL-5317_C.dwg

6151i?

Preferred channel alignment / design channel alignment

Concrete blocks

PLAN N.T.S.

Willows 2.5m

Wire rope to be looped around willows

00 gt 9 g

g

tg . 9,0gogogo.

1.4gogilAr'

0.2m - 0.3m

Preferred channel alignment/ design channel alignment

12mm diameter wire rope Willows

ELEVATION N.T.S.

DISCLAIMER:




NOTES:

• Where the willow trees or branches overlap, the upstream willow is to be on the outside (riverside).


DESIGN DRAWN

VERSION # 1 EROSION REPAIR COMPILED April 2013

April 2013 P.COOK CHECKED 3pr/0

10E01 greater WELLINGTON REGIONAL COUNCIL

SMALL STREAM / RIVER STANDARD DETAIL

TETHERING (CABLED WILLOWS)

C -C-44(4414

APPROVED Drawing No. RL-5317 / 7

Te Pane IVIatua Taiao FILE N/50/2/6 Cad: RL-5317_C.dwg

10m crs

NOTES:

Wire rope to be looped around willows • Where the willow trees or branches overlap, the

upstream willow is to be on the outside (riverside).

Willows

0.8m x 0.8m x 1.6m concrete blocks

Wire rope to be looped around willows

<

Willows

N Wire rop looped

around willows 30°

Willows Tree root system

/ / 12mm Dia.

Wire rope

0.8m x 0.8m x 1.6m concrete blocks

12mm Dia. Wire rope

PLAN N.T.S.

ELEVATION N.T.S.

VERSION # DESIGN EROSION REPAIR DRAWN 1 COMPILED P.COOK

April 2013 April 2013

CHECKED 315111 APPROVED

C-C-MAktiki greater WELLINGTON c/10

REGIONAL COUNCIL


TREE GROYNES (TRENCHING WILLOWS) Drawing No. RL-5317 / 8 FILE N/50/2/6 Cad: RL-5317_C.dwg Te Pane Matua Taiao

N-

DISCLAIMER:





FILE N/50/2/6 Cad: RL-5317_C.dwg


Te Pane Matua Taiao


STANDARD DETAIL Hard Edge Works (Concrete Block or Gabion Groynes)

VERSION # 1

NINON

Plant willows between groynes \,/

6 BLOCK GROYNE

N.T.S.

.1/

Preferred edge of channel

Preferred Channel

3 BLOCK GROYNE

N.T.S. OBJECTIVE

Concrete block / gabion groyne

Gravel removed from beach to fill

■ eroded channel Erosion face

TYPICAL CROSS SECTION N.T.S.

Front edge of top block In-line with edge of preferred channel

Reformed channel

Plant willows between groynes

Preferred edge of channel


Front edge of top block In-line with edge of preferred channel

_

1

, . . 1 , . 1 Y 1

. I < ) First row of blocks dug into bed below scour depth

To repair the existing erosion and return the channel to its prior alignment and hold it there by constructing hard edge works with either concrete blocks or gabion baskets.

MATERIALS

Use 0.8m x 0.8m x 1.6m concrete blocks (or similar) preferably with centre holes or lifting eyes for wire rope to loop through. 14mm 0 wire rope. Wire clamps. Tree willow poles (Moutere).

METHOD

Use an excavator to shift the flow channel back to its pre-erosion alignment. Fill the current erosion with gravel excavated from the proposed 'restored channel alignment or from the built up beaches opposite.

Construct a series of concrete block groynes along the outside edge of the alignment. Blocks set back to of block length and roped together securely.

Groyne spacing is a judgment call depending on factors such as tightness of the bend, stream gradient and bank material etc. A general rule of thumb is : Groyne spacing = 1.5 x the distance between Erosion face and preferred channel alignment

Install groyne pointing slightly upstream with a slight lean forward

All blocks to be roped together with 14mm 0 wire rope so they act as a single unit.

It is essential that the bottom layer of blocks is below scour depth or the groynes will rapidly fail.

The large groyne (6 block) is normally used at the apex of the bend.

The area between the groynes is then mass planted with willow poles.


Good, provided the bottom layer is well founded below scour depth and all blocks secured together with wire rope to act as one unit.

NOTES:

Willows must be protected from grazing stock. Gabions may be substituted for concrete blocks (all the above applies except that in some circumstances gabions have a shorter life). Gabions will likely be damaged & fail in highly mobile gravel beds.

Refer to drawings HR-5317 / 2 to 4 for notes on planting willows

DISCLAIMER:





DESIGN DRAWN CHECKED

COMPILED P.COOK

C-C-Atidtant APPROVED _C/16Q. bj 51 1.3 Drawing No. RL-5317 / 09

April 2013 April 2013 315-1)3

NOTES:

• All irons to be in good condition without significant corrosion.

• Wire cable to be 14mm 0 3 x 19 Galvanised wire rope.

• Cables tied off every eighth iron (28m).

• Cable tensioned to a nominal strain using a "come-along" or 'Tuner winch.

• In each bay the fascine is to be cabled together and weighted with a 2.5 tonne concrete anchor block located immediately underneath the fascine.

• Every set of three adjoining Railway irons to be tied back to a 2.5 tonne concrete anchor block located 10m from the line of the rail piles and buried lm Min. below ground level.

• Where the willow trees or branches overlap, the upstream willow is to be on the outside (riverside).

• Rail piles to be located on the river design channel / preferred channel alignment. The area between the river bank and piles is to backfilled with river gravels as necessary.

• At the upstream end the rail piles and wire cables are to be returned into the bank as a Rail iron groyne 4 bays into the bank.

• Refer also GWRC Drawing A2-9459 / 1-RC for further details.

Concrete anchor block every wired to 3 rail piles and buried 1m Min. , below ground 1 vel

River bank

14mm 0 wire rope

3 wire cables connecting piles. Bottom cable located at water level

Fascine of willows placed horizontally between river bank and piles

Willow poles

,0.1m

0.5m

0.5m

Low flow water level

Fascine wrapped together each bay (10.5m) with 14mm 0 wire rope and weighed down with a 2.5 tonne concrete anchor block located immediately underneath fascine

70 lb yard Rail iron piles or similar.

DETAIL N.T.S.

DISCLAIMER:


This plan has been prepared to offer assistance to rural landowners, the landowner is under no obligation to cany out these works. In areas of significant erosion, detailed engineering design / investigation may be required.



Willow poles

Willow fascine

Min. bed level / scour depth


14mm 0 Wire rope

10m

.2.gogo Low flow water level V Erosion face

gi%Z: 44g,c;g ggg4zgzggg 0`4,gg'4,ggggg

14mm 0 wire rope


Rail pile


VERSION # COMPILED April 2013 1 EROSION REPAIR


PILE and FASCINE REVETMENT PROTECTION

DESIGN DRAWN CHECKED c-mcfmA4 APPROVED Drawing No. RL-5317 / 10


P.COOK April 2013 3/5113 6is713

Te Pane Matua Taiao FILE N/50/2/6 Cad: RL-5317_C.dwg

Cad: RL-5317_C.dwg FILE N/50/2/6

NOTES:

To suit site (but not too heavy)

100 x 50 horizontal timbers facing downstream side

100 x 20 or 150 x 25 timber

Swinging gate detail N.T.S.

Loose chain gates together so stock can't push through

Cut groove for wire rope at top of strainer posts

Tie back to ground anchor

4,1 Iktsk

• These gates float in a flood and pose minimum restriction to flows and catch minimum debris.

• All timber to be treated as required

Fix wire hangers so gates can't slide out of position

Hang so timber is just out of the water in normal winter flow

Heavy wire rope

Wire rope to buried - anchor eg. concrete block

Strainer posts 1m Min. from bank edge TYPICAL DETAIL OF STREAM CROSSING

N.T.S.

To suit site

DISCLAIMER:





Strainer post Strainer post

Swinging gate

100 x 100 timber rail

Fix wire rope here

Strainer post

Tie back to bottom of post

Wire rope

Alternative for strainer unit N.T.S.


STANDARD DETAIL STOCK FENCE ACROSS SMALL STREAM

DESIGN DRAWN CHECKED C—C, MwAtAt APPROVED Drawing No. RL-5317 / 11

3t5-/i3 61C1

COMPILED P.COOK


Te Pane Matua Taiao

small stream erosion repair · 2013. 5. 7. · best practice guide version # 1 – april 2013 small...

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