Thursday, 27 April 2017

Small Pond Installations for Irrigation and Wildlife - Part 1

We've done a couple of pond installations recently, one for our new perennial polyculture trial garden (Ataraxia) and another for a permaculture farm/orchard I designed for Catherine Zanev and Adjmal Dullo from Venets Ltd.


Wildlife ponds in our gardens

I thought I'd write a post to share our experience and provide an overview of our pond design and installation process. In this post we'll look at locating a pond, pond design and pond digging and in a future post I'll write about lining, planting and landscaping the pond.

Introduction 


In both the recent ponds we dug we hired a machine and driver to carry out the dig. Previous ponds we've dug by hand. With some willing help a 6 x 4 x 1.5 m pond is very do-able and I'd estimate that  3-4 people with good tools would take about 8- 10 hrs on moderately light soils, probably longer in clay.

The Pond in the Paulownia Garden - dug by hands 

The recent ponds we made required 3 and 4 m depths and were larger in surface area so we opted for machines. For the pond in the new garden (Ataraxia) we used a mini digger and it took us approximately 7 hours to dig 10 m x 6 m x 3.5 m. The soil is sandy silt full with smooth boulders ranging in size from basketballs to tennis balls.  

Larzar and his mini-digger at work in the new perennial polyculture trial garden (Ataraxia)

For Catherine's pond we used a JCB excavator. I was planning to use a JCB back hoe but the excavator turned up and actually I was really pleased with the machine. Perhaps the front bucket on the back hoe would have cleared the top soil a little faster but the excavator made a great job of...er.... excavating :)  It took around 5 hours to dig a 12 m x 6 m x 4 m hole, to level the 2 m wide pond walls, make a 30 m inlet swale and a 15 meter spillway. The soil is heavy clay.


The JCB excavator starting the dig at Catherine Zanev's permaculture farm  

So here's an overview of our design and installation process.


Pond Design and Installation Overview


Check the legalities and regulations of building a pond in your area. For ponds containing over 200 m3 of water and ponds on steep slopes with retaining walls that will bear a lot of weight, it's best to seek professional advice and guidance before you start.

Selecting a Location


Topography - Based on the topography of the site we select the optimal location for the ponds and work out the positions of the inlet (where the pond receives water) and outlet (the exit point for overflow from the pond).

Google earth  image of Ataraxia with 1 m contour intervals extracted from a Digital Terrain Map (DTM) DTM supplied by Geodetect, data extracted by georgipavlov.net


Pond placement in the north east corner of the site is the highest point of the site and provides opportunity to siphon water from the pond for irrigation. We have access to a stream that can be diverted from the N.E to fill the pond. The beds are placed more or less on contour to ease irrigation.     


Surroundings - The pond location will benefit from protection from strong winds and some shade (to reduce evaporation). Having lots of deciduous and fruiting trees around the pond will result in large quantities of leaf and fruit falling into the pond that can cause eutrophic conditions unless cleared, and digging a pond around established trees will also inevitably damage the roots of the trees.


What is the pond for?


Clarifying your objectives for having a pond is important and determines the shape and size of the design.

If you would like to encourage wildlife you will need to provide various depths within the pond to cater for a range of aquatic plants and you'll need a gentle slope for animals to enter and exit. Eventually, adding some features such as tree stumps or hollow rocks to the pond will provide hiding places for fish and other pond life and basking territory for amphibians.


The four categories of plants that should be present in a wildlife pond  Emergents (Marginal Plants) - Deep Marginals (Rooted Floating Plants) - Oxygenators (submerged plants) - Floaters (free floating plants) 

Installing a pond is probably the single most effective thing you can do in a garden to enhance biodiversity and wildlife and the majority of the wildlife that will be attracted to the pond will be of great benefit to your garden or farm, i.e pollinators and pest predators. For a wildlife pond a maximum depth of 1.3 - 1.5 m is adequate. At this depth most aquatic organisms including European carp -Cyprinus carpio can survive the winter.

Frogs and Toads are excellent predators of slugs and grubs in the vegetable garden 

If you need the pond for irrigation and do not have another source of water available it's best to dig deeper both to store more water and to moderate the water temperature to reduce the evaporation rates. Deep water stays cooler for longer and moderates the temperature of the surface water and water in the shallows that will warm much faster and evaporate quickly.
  

Sketching the Pond Design



I make a few simple drawings showing the boundaries and dimensions including an overhead view and a cross section of the width and length. This helps clarify how the pond will look and function. If using a hired machine/driver these sketches will also help communicate your vision.

The below sketches are for the pond we installed at Catherine Zanev's farm where the objective was to store rainwater from surface runoff during storm events for irrigation, but also to provide habitat for a range of wildlife and aquatic plants, hence we included shelves and beaches in the design.  

Overhead sketch
   
Cross section sketch 

Marking the shape of the pond and where the depth changes occur on the land also really helps.  A long rope works well for this as do stakes connected with string or spray paint.  

Installation Day


Pegging out - Get on site well before the machine arrives and mark clearly all relevant features of the pond such as the perimeter, the width of the wall, the path of the inlet and spillway, the locations of depth variation and the highest and lowest points of the land that the pond will be placed.

Me and Stoyan Georgiev pegging out the spillway using a transit level.

Planning  Soil Deposits
- Select an area where the top soil and excess sub soil can be stored. Most of the sub soil can be used for a wall on the lower section of the pond (if working on a slope) or as bank around the perimeter of the pond if working on level ground and your potential water source is higher than the wall height. In some cases you may have excess soil. Have a plan for where to put it and how you will get it there.

It's also worth planning the route for the machine to enter and work in to avoid soil compaction and damage as much as possible and to restrict this to as small a space as possible.


Communicate the plan - When the driver arrives explain exactly what you want to do and why you want to do it as clearly as possible before works begins. An experienced operator will most probably have a good understanding of the fundamentals and may be able to offer some advice so it's a good idea to invite the drivers opinion.

Remove Top Soil - First off remove the top soil from the pond area and from the area around the pond where the wall will be placed, The top soil is very valuable and can be used to dress the excavation at the end, helping to hasten revegetation. It can also be used in another area of the garden/farm.  


30- 40 cm  of top soil is removed and stored separately for later use 
Start digging from an outside edge and dig down to the deepest part of the pond to assess the soil profile and depth. It may be you have planned 4 m depth but hit bedrock after 3 m. Once you have established the depth you can start to distribute the sub soil to build up the lower sides of the pond. The excavator made a great job of compressing the various layers of soil that were piled up on the edges with the flat side of the bucket. A 2 m wide wall base is very secure for a pond of this size (12 m x 6 m x 4 m).



Sub soil used to build a 2m wide retaining wall 
Get the levels right  - If your water input is at ground level remember the highest level the pond water will reach will be no higher than the input source and once the pond fills to this level it will start to back flood.

An overflow route that will slowly disperse the water should be implemented.  For the above pond design we lowered a section in the wall to disperse overflow into a 16 m swale that runs just slightly off contour into the adjacent fields.

Having a transit level on site you can quickly check levels as you go to make sure the walls are high enough and that the overflow is where it should be.

We used the top soil to build a berm slight off contour to disperse any potential overflow water into the fields. 

Any earthworks that we are sure won't be disturbed in the near future we re-apply the top soil to and sow with a cover crop. In this case we used Trifolium repens - White Clover at a rate of 1.5g /m2 for the inlet and outlet swales.  


Trifolium repens - White Clover  


Following the dig, the deposited soil will sink and settle over the next few weeks. A few heavy rains will encourage the settling of the soil. After the soil has settled, we check the levels  again and make any necessary adjustments before lining the pond.

In a following post we'll look at liner options, how to install a liner, planting out the pond, landscaping the pond banks/earthworks and pond maintenance.

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