Too much rainwater ???

[Steveg]

I am considering diverting rainwater from a down pipe on my house to my small garden pond. At times the pond would then overflow onto the surrounding land , which is fine . BUT are there any disadvantages to the ecology of the pond if the water exchange is high during rainy spells. Thanks Steve G

 

[koiguy1969]

debris and chemicals that could leech from your roofing materials and into the pond water could be a real issue for concern.

 

[ponderpaul]

I have used rainwater caught and stored in barrels to top off my pond for nearly three years without problems. The roof is several years old so that chemicals will have leached out a great deal. I might be concerned with a newer roof. Also, any dirt or debris from the roof has time to settle out before it goes into the pond.
At times, the pond will run over just from rain alone (as recently as yesterday). By way of explaination, I have bog and stream with about half the surface area of my pond so the amount of rain multiplies in volumn in the pond.

 

[CometKeith]

Essentially you are doing a large scale water change. I would avoid letting the storm water runoff replacing more than 50% of the pond's volume and you may need to figure out how much water your drains produce. The rainwater could change the PH, dissolved O2 levels, and chemical balance in the pond and it may cause your fish to get stressed.

 

[JoaniePA]

Depends on where you live. We have a rain barrel and considered the same. Some posted here that we should consider what falls on the roof, into the gutters, and into the barrel before we use the barrel water. Aside from the leach from shingles etc, whatever comes down there is concentrated by routing a large roof surface of water down into the gutters. After we thought about that we realized that every week or two, for most of the pond season, we are cleaning heavy pollen off of our porch furniture, not to mention the dirt and dust from the busy road that runs near the end of our property. Even if it's not toxic, nature takes care of what falls onto the ground and across the small surface of the pond, but I can't imagine it's a good thing to concentrate it into the gutters, then a rain barrel, and then into the pond. I'd use it just for plants.

 

[DrDave]

Joanie makes a good point, there are areas that have residue in the air that could carry toxic material to your roof. Some of these elements may not harm your fish the first time, but could build up over time since some are heavy and rest on the bottom of your pond.
If you are doing this, test your water after each rain and make sure it is safe. When doing a water exchange, make sure you are drawing from the bottom to avoid the buildup.