Initial Design Considerations for your Garden Pond
Size        Depth        Shape        Capacity        Species of Fish        Profile
The design of your pond and its location are very closely linked but I have tried to separate them on this site so that I have a bit more freedom with my pages and I think it helps to clarify some points.
When you begin to consider the location of your pond, you need to decide what it is that you want from it. For example, if you really only want a small pond for a natural habitat for frogs, newts etc, your choice of location will be much wider than if you want a formal pond for keeping large fish. Equally, if you decide to have a deep pond, there may be areas in your garden that will not be suitable because you have underground pipes for water, drainage etc. (Covered on the location page.)
Whatever you do, don't rush into this decision. The size of the pond needs to be in-keeping with the rest of your plans for your garden. A tiny pond in a large garden often looks as if it was put there by mistake. But one that is too big for its surrounds can also spoil the overall effect. My experience shows that the bigger the pond, the more pleasure you will derive from it. Here are some things to consider before you make your final decision:  Top
If you are going to keep fish in your pond, it needs to be at least 500mm deep so that the water will not be too cold for the fish in the winter or too hot for them in the summer. If you are planning on keeping Koi, the books all say that you should really be thinking of a depth of at least 1 metre. In my ponds, I compromise. There are certain parts of my anatomy that definitely do not like getting into very cold water and as you never know when you might need to get into the water for maintenance, even in the winter, I make sure that I can reach all parts of the pond without getting those parts of me wet and hence cold. You might be thinking that a pair of waders could solve that problem but you need to be in bare feet whenever you step into the pond so that you can feel any tiny particles of grit before you put any weight on them and press them into the liner. Remember also that different plants thrive at different depths, so if you have a particular favourite, you need to ensure that your pond provides the correct environment for it.   Top
If you are going to have a natural looking pond, edged with rocks and plants, you can easily create informal curves in whatever shape you like. However, if you intend your pond to be positioned next to a patio or decked area, it might not be possible to have the same types of curve and it may be necessary to have a straight part. The main thing is to ensure that your pond matches your garden. By that I mean that if the rest of your garden is laid out in a formal design, an odd shaped pond wouldn't look right. Equally, in a natural or semi-wild informal garden, a formal rectangular pond would not be right. The exception to this general rule is for Koi keeping. Koi ponds tend to have clean square lines so that the fish are the whole focus of interest. For that reason, they are often devoid of plants and have a smooth almost flat bottom.   Top
Pumps and filters are dealt with on other pages but they are related to the size of the pond and not just to the amount of water that you want to have coming over your waterfalls. The pump needs to move the full capacity of your pond through the filter in a reasonable amount of time but not too fast that the filter cannot do its work. Generally, the bigger the pond, the more powerful the pump will need to be and the bigger the filter. Therefore, your pump and filter will be more expensive. Another thing that is often forgotten is the cost of the water. Most houses now have meters on their water supply so there will be a cost for filling and topping up your pond that you will need to factor in.  Top
Goldfish, Shubunkins, Comets and Orfe will be quite content in the minimum 500mm of water but if you want to keep KOI Carp, the pond should ideally be at least 1000mm deep. The fish-keeping reference and guide books all state that each square foot of pond surface area can support 1" of fish. My experience is that as long as you provide a regular supply of food and maintaining a well balanced pond, then it will support may times that amount of fish. Unfortunately, there is a down side to that. The bigger the fish, the more waste they produce and hence the bigger the filter needed to keep the water clean. So if you hope to grow the really big Koi, you will need a really big pond and a potentially very expensive filter system. There is no possibility of compromise here.   Top
Check your friends' ponds
If you know anyone with a pond, go and talk to them about their design and how they reached their decisions. People with ponds love to talk about them and are usually only too happy to discuss the problems they found and how they overcame them. I cannot stress enough that this is the time to take your time. If you get this wrong, the end result could be expensive, because once you have built your pond, you will invariably have to replace the parts that you don't like and that always costs significantly more than any slight adjustments at the design stage.
If after all this you still are not sure, this is a good rule of thumb.
Think of the size you want, double it, think about it again, and then make it bigger still.
Of all the people I know who have built garden ponds, the majority have rebuilt their ponds within 2 years of the first one. Every one of the people that I have designed ponds for has agreed that their initial plans were not bold enough and that they were delighted that they went for a bigger pond than they first envisaged.  Top
As well as deciding on the overall size and surface shape you need to consider the underwater profile of the pond. Again, a number of factors are tied into this decision. For example, if you intend to keep specimen Koi Carp, you will need a pond that has clean, straight, almost vertical sides and a nearly flat bottom with just a slight slope towards a centre drain. However, if you want a more natural pond, you need to plan places to put plants, some of which will need a fairly large platform not too far below the surface. If you refer to any book in a garden centre about how to build a pond, they will invariably suggest a shelf around the pond about 20cm below the surface of the water so that you can place marginal plants. That part must have been written by a heron breeder because that sort of shelf is exactly what herons love to find. On it they can stand in shallow water and patiently wait for your fish to come to lunch. You do need to think about your marginals of course, but unless you are going to fill the shelf completely with flowers / plants, an all-around shelf is not a good idea.
I like to try to get a number of different levels within my pond so that I have the maximum flexibility when it comes to selecting plants.
Different levels probably make it more interesting for your fish as they swim about exploring their environment each day.
Another advantage of having different levels within your pond is that it gives you the opportunity to move your pump to a slightly shallower depth in the winter. As you will see from the Pumps section, there are good reasons for running your pump all year round, but that also causes potential problems. Having the ability to raise the pump can overcome them.  Top