In response to your first question concerning the pump. What you didn't mention is the performance of the pump at different head, i.e. how much water flow does it deliver at the highest point. You also need to calculate the head loss of the piping/plumbing you use. Most pumps (at least here in the states) include a chart showing the pumps capacity at various head levels. Also keep in mind that head is measured from the water surface and not ground level.

Question 2. Koi and goldfish love a strong current in the pond as long as they have some little area they can go to rest. They will often be found playing in the strong currents from a waterfall or under water return.

Question 3. Koi and goldfish are "coldwater" fish and will survive winters just fine as long as you keep a small hole in the ice and the water in the pond doesn't freeze solid. They may appears listless or dead in the spring but as the water warms they almost always come. I think your pond is deep enough that you won't have to worry, especially if you keep a tank heater (like the ones farmers use it stock tanks) in the pond in winter.

4: I would use goldfish and not too many. Koi will get big and make a lot more waste than the goldfish. Oh, and don't use the "fancy" goldfish as they are not as hardy as the regular ones.

5: You can go either way on this one. Some people I know turn their pumps off other (like me) keep them running year round. The main issue is to keep enough oxygen in the water for the fish. In any event with your winters I would put in a waterfall bypass and return the water directly to the pond and not use the waterfall during the winter. Running water in the waterfall during the winter is a request for disaster. The water will gradually freeze and often will cause the water to escape the confines of the normal water column resulting in a drained pond and lost fish.

6: Just keep the pump running to keep the water oxygenated.

7: I am not an advocate of putting gravel in the bottom of a pond. It is a recipe for disaster if you have fish. All the fish waste gets in and under the gravel and it is very hard to keep it clean. This results in a layer of nasty bacteria beneath the gravel which will eventually be harmful, even fatal, to your fish. A gravel less bottom makes cleanup easy

There are a lot of aquatic plants that will grow in your environment. you can use marginals and set them on the "steps" and maybe one hardy water lily in the deep or next step up. Floating plants do will in a pond as well. Of course this all depends on how much sun the pond will get.

DO NOT use any "potting soil" in the pond. You can plant most plants in pea gravel and they will do fine. Some people use regular old clay soil with nothing added but I find that the fish like to dig in it and then it gets all over the place and the plants end up floating out of the pots.

I'm sure you will get lots of good advise from the users of this forum. everyone here is very helpful and knowledgeable.

Best wishes on your journey into ponding.

Thanks for you answers that was wonderful.

you mentioned about the pump height and you must have missed it because I did mention it. It pumps to a height of 17feet. (5.2meter)

I will have one line running from the pump (obviously lol) and it will split into 3 to feed the waterfalls using flexible hose.

I had read that my pond is too small for koi fish and that goldfish were the way to go and to figure about 50 gallons to a goldfish. Would you agree with that?

I'll take your advice and not do the gravel in the bottom. I don't want to make life harder than it has to be.

Also to clarify the pond surface will be at just about ground level. The deepest part of the pond will be around 5 foot deep (1.6meter) and from the bottom at the deepest part on the sides with the "steps" it will go up a meter and plain off for 30cm then go up 30cm and plain off 30cm then go up 30cm to ground level.

sorry forgot to mention that I will keep a separate aerator going 24/7 so there is always something going when the pump for the waterfall isnt on.

I think cherokee did a great job and has covered most of your questions clearly. I was too lazy to try and fight my way through your diagram. I just want to be sure that you really need the 3x volume for the pump. Most designs have water flowing from one height to the next lower and therefore only 1x flow is needed. I guess that in this case, you are building three separately accessed falls and that they are 15 to 17 feet above the pump or lower pool. If so, than an additional issue is that you will probably need two valves in your split lines to assure proper flow to each of your spillways because they are at varied heights and therefore pressures. This is a lot of height and flows will likely be severely decreased in any case.

I wanted to mention the problems with not running the falls (pump/filter)24/7. Your pump feeds the filter(s) where most of the aerobic bacteria live and break down waste. Turning off the flow will cause them to start to die-off within a very brief time. The good bacteria requires lots of oxygen to keep the water from becoming very stinky. The lack of oxygenated water encourages the growth of anaerobic bacteria which is definitely not a good thing. That is the stinky part. Turning off the filtration system essentially turns the pond into a sewer.

It is not good for the fish, especially when it is warm. They can do with somewhat less oxygen in cold water(under 55oF) when they become torpid and stop eating but definitely not when it is above 55oF. I use a bubbler all year which also helps keep a hole open in the winter ice.

Thanks for your answers you guys.

Chas: in regards to the valve thingamajig. My husband will be the one that does the plumbing so I will mention that to him though I am sure he probably already knows about that sort of stuff (he's real handy)

Sleepless:

I intended on using a skippy filter with a seperate pump just for the filter and reserve the waterfall pump solely for when i want to run the waterfall. (it saves money in the long run because the filter pump requires less watts than my waterfall pump 65watts for the filter and 205 for the waterfall)

I have another post on here about the skippy filter but that was so I could see if I could make my waterfall out of the skippy filter with the set up I mentioned in that post and do away with the expensive pump in my original design all together. (of course having to change the waterfall placement from what it is originally designed to be)

Sorry for all the chaos but its difficult for me to plan all this from the Netherlands when I come from the US and only speak English. I have to research only in English and then take what I learn and try to find the things and/or equivalents here or to see if i can have them shipped here which requires me to do very advanced planning before I make a move on something and oftentimes requires me to rethink plans to try to find a better or more economical way to get to the desired end. Its really a pain!!!