# Using bags of concrete to dam a small stream? **URL:** \ **Category:** Factual Questions\ **Created:** [December 15, 2018, 3:44am UTC](https://boards.straightdope.com/t/using-bags-of-concrete-to-dam-a-small-stream/826158 "2018-12-15T03:44:47Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Mangosteen](https://avatars.discourse-cdn.com/v4/letter/m/6a8cbe/32.png) [@Mangosteen](https://boards.straightdope.com/u/Mangosteen)\ **Post date:** [December 15, 2018, 3:44am UTC](https://boards.straightdope.com/t/using-bags-of-concrete-to-dam-a-small-stream/826158/1 "2018-12-15T03:44:47Z")
There is a small stream on my property here in Hawaii. I want to partially dam it and create a small pond on the down side of the dam so my ducks have some place to swim. There are some large rocks in the stream, but not enough for what I want to do. Will the bags harden and become “rocks”? I don’t plan on opening the bags. I just want to place them in the stream, paper bag and all. Should I use mortar, cement, concrete mix or something else? ---
**Author:** ![mixdenny](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mixdenny/32/2962_2.png) [@mixdenny](https://boards.straightdope.com/u/mixdenny)\ **Post date:** [December 15, 2018, 3:57am UTC](https://boards.straightdope.com/t/using-bags-of-concrete-to-dam-a-small-stream/826158/2 "2018-12-15T03:57:24Z")
Oh, they will definitely harden. I’ve got a few around here. You might want to punch some small holes in them as some have plastic liners. Might as well use concrete although I doubt it matters much. Bear in mind most states take a dim view of damming waterways. They made my uncle flatten the simple rock dam on his property a couple of years ago. But they only knew about it because a neighbor complained. It had been there since the 1940s. We used to busy ourselves every summer piling rocks on it. It raised the water 8-10 inches. Dennis ---
**Author:** ![Beckdawrek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beckdawrek/32/3647_2.png) [@Beckdawrek](https://boards.straightdope.com/u/Beckdawrek)\ **Post date:** [December 15, 2018, 4:02am UTC](https://boards.straightdope.com/t/using-bags-of-concrete-to-dam-a-small-stream/826158/3 "2018-12-15T04:02:43Z")
Yeah they will harden. Be aware who is downstream. They may not appreciate it. ---
**Author:** ![lingyi](https://avatars.discourse-cdn.com/v4/letter/l/d2c977/32.png) [@lingyi](https://boards.straightdope.com/u/lingyi)\ **Post date:** [December 15, 2018, 4:36am UTC](https://boards.straightdope.com/t/using-bags-of-concrete-to-dam-a-small-stream/826158/4 "2018-12-15T04:36:08Z")
> [@mixdenny](#): > > Bear in mind most states take a dim view of damming waterways. They made my uncle flatten the simple rock dam on his property a couple of years ago. But they only knew about it because a neighbor complained. It had been there since the 1940s. We used to busy ourselves every summer piling rocks on it. It raised the water 8-10 inches. > > Dennis This. Unless the stream somehow starts and ends completely on your land (extremely unlikely), The waterway is likely protected by the County, State or Federal laws and use guidelines. More importantly: "Aloha 'aina simply means to love and respect the land, make it yours and claim stewardship for it. Malama 'aina means to care for and nurture the land so it can give back all we need to sustain life for ourselves and our future generations, and, An ahupua’a is an ancient concept of resource use and management based on families living in a division of land that connects the mountains to the reefs and the sea." - Puanani Rogers, Team Leader for the Ho`okipa Network [http://www.sustainablemeasures.com/Training/Indicators/Def-Hawi.html](http://www.sustainablemeasures.com/Training/Indicators/Def-Hawi.html) Edit: While the concrete will eventually set, it will be sending possibly harmful substances down the steam. AUWE! Edit 2: +1 to beckawreck’s post! ---
**Author:** ![nearwildheaven](https://avatars.discourse-cdn.com/v4/letter/n/90db22/32.png) [@nearwildheaven](https://boards.straightdope.com/u/nearwildheaven)\ **Post date:** [December 15, 2018, 4:38am UTC](https://boards.straightdope.com/t/using-bags-of-concrete-to-dam-a-small-stream/826158/5 "2018-12-15T04:38:07Z")
Before doing something like that, get permission first. :smack: ---
**Author:** ![lingyi](https://avatars.discourse-cdn.com/v4/letter/l/d2c977/32.png) [@lingyi](https://boards.straightdope.com/u/lingyi)\ **Post date:** [December 15, 2018, 5:03am UTC](https://boards.straightdope.com/t/using-bags-of-concrete-to-dam-a-small-stream/826158/6 "2018-12-15T05:03:37Z")
Sometimes beaver dams have to be broken down sometimes because they cause environmental problems, but up and downstream. ---
**Author:** ![lingyi](https://avatars.discourse-cdn.com/v4/letter/l/d2c977/32.png) [@lingyi](https://boards.straightdope.com/u/lingyi)\ **Post date:** [December 15, 2018, 5:25am UTC](https://boards.straightdope.com/t/using-bags-of-concrete-to-dam-a-small-stream/826158/7 "2018-12-15T05:25:53Z")
> [@lingyi](#): > > Sometimes beaver dams have to be broken down sometimes because they cause environmental problems, but up and downstream. WOW lingyi! “Sometimes beaver dams have to broken down because they cause environmental problems, both up and downstream” ---
**Author:** ![Mangosteen](https://avatars.discourse-cdn.com/v4/letter/m/6a8cbe/32.png) [@Mangosteen](https://boards.straightdope.com/u/Mangosteen)\ **Post date:** [December 15, 2018, 7:04pm UTC](https://boards.straightdope.com/t/using-bags-of-concrete-to-dam-a-small-stream/826158/8 "2018-12-15T19:04:00Z")
> [@lingyi](#): > > This. Unless the stream somehow starts and ends completely on your land (extremely unlikely), The waterway is likely protected by the County, State or Federal laws and use guidelines. > > More importantly: > > "Aloha 'aina simply means to love and respect the land, make it yours and claim stewardship for it. > > Malama 'aina means to care for and nurture the land so it can give back all we need to sustain life for ourselves and our future generations, and, > > An ahupua’a is an ancient concept of resource use and management based on families living in a division of land that connects the mountains to the reefs and the sea." > > - Puanani Rogers, Team Leader for the Ho`okipa Network > > [http://www.sustainablemeasures.com/Training/Indicators/Def-Hawi.html](http://www.sustainablemeasures.com/Training/Indicators/Def-Hawi.html) > > Edit: While the concrete will eventually set, it will be sending possibly harmful substances down the steam. AUWE! > > Edit 2: +1 to beckawreck’s post! Hawaiians have been diverting waterways (with good reason) since time immemorial to irrigate crops, create fish ponds, control flooding, etc. I’m just trying to make a 5 foot wide, 12 inch deep pond for my ducks, Jasper and Genevieve. If cement contains harmful chemicals, we’re in trouble because there is a large concrete bridge that the stream runs under before it passes through my property. The amount of trash that I remove out of the stream bed after a heavy rain is unbelievable. Next stop for the water (and trash if I don’t fish it out) is the Pacific. I think I’m doing my part for the 'aina. No neighbors downstream. Breaking laws? Ever speed on the highway, smoke pot, jaywalk, download music illegally, drink under age, share meds, gamble, etc. “He who is without sin,…” ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [December 15, 2018, 7:14pm UTC](https://boards.straightdope.com/t/using-bags-of-concrete-to-dam-a-small-stream/826158/9 "2018-12-15T19:14:10Z")
> [@Mangosteen](#): > > “He who is without sin,…” '_Mother!_ :mad: ’ ---
**Author:** ![lingyi](https://avatars.discourse-cdn.com/v4/letter/l/d2c977/32.png) [@lingyi](https://boards.straightdope.com/u/lingyi)\ **Post date:** [December 15, 2018, 8:10pm UTC](https://boards.straightdope.com/t/using-bags-of-concrete-to-dam-a-small-stream/826158/10 "2018-12-15T20:10:10Z")
I couldn’t edit by post, but I wasn’t talking about hardened concrete, but the raw materials in the mix before it cures/sets. As for your idea of “care” for the 'aina, I hope when you get neighbors downstream, they’re marching solders! ---
**Author:** ![Mangosteen](https://avatars.discourse-cdn.com/v4/letter/m/6a8cbe/32.png) [@Mangosteen](https://boards.straightdope.com/u/Mangosteen)\ **Post date:** [December 15, 2018, 10:52pm UTC](https://boards.straightdope.com/t/using-bags-of-concrete-to-dam-a-small-stream/826158/11 "2018-12-15T22:52:43Z")
If there are harmful chemicals in the cement mix, when the bridge that is above my home was built, massive amounts of those chemicals must have washed down the stream. The concrete in the bridge wasn’t mixed elsewhere, hardened and brought to the site. Compare the chemical bath that the stream took when the bridge was built with amount chemicals that might be in the 5 bags I plan to use and there is a huge difference. If you think removing trash out of a stream before it winds up in the ocean is not taking care of 'aina, I’d like to know what you would call it. I’ll never have neighbors down stream. I’m at the end of the stream. It empties into the ocean after it passes me. ---
**Author:** ![GreysonCarlisle](https://avatars.discourse-cdn.com/v4/letter/g/a87d85/32.png) [@GreysonCarlisle](https://boards.straightdope.com/u/GreysonCarlisle)\ **Post date:** [December 15, 2018, 11:08pm UTC](https://boards.straightdope.com/t/using-bags-of-concrete-to-dam-a-small-stream/826158/12 "2018-12-15T23:08:22Z")
I’ve never seen a wall like that built to hold water, but I’m sure it’ll work. I’ve always liked the looks of them after the paper is gone. [Directions for the land-based type](https://www.hunker.com/13414694/how-to-make-retaining-walls-out-of-concrete-bags). Some people take an ice pick to each bag, and some sink rebar through the bags. Ask your local concrete supply if they sell bags explicitly for that purpose. ---
**Author:** ![Twoflower](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/twoflower/32/22_2.png) [@Twoflower](https://boards.straightdope.com/u/Twoflower)\ **Post date:** [December 15, 2018, 11:10pm UTC](https://boards.straightdope.com/t/using-bags-of-concrete-to-dam-a-small-stream/826158/13 "2018-12-15T23:10:16Z")
I don’t know about Hawaii state laws, but as far as federal laws are concerned, your project is covered under the Clean Water Act. And, as long as you’re placing less than ten yards of fill below the high water line, you’re completely legal under [Nationwide Permit 18](https://usace.contentdm.oclc.org/utils/getfile/collection/p16021coll7/id/6711). ---
**Author:** ![ZurBob](https://avatars.discourse-cdn.com/v4/letter/z/71e660/32.png) [@ZurBob](https://boards.straightdope.com/u/ZurBob)\ **Post date:** [December 15, 2018, 11:19pm UTC](https://boards.straightdope.com/t/using-bags-of-concrete-to-dam-a-small-stream/826158/14 "2018-12-15T23:19:56Z")
> [@lingyi](#): > > I couldn’t edit by post, but I wasn’t talking about hardened concrete, but the raw materials in the mix before it cures/sets… Stone, sand, and Portland cement are the _only_ components in concrete mix… other than (perhaps) a temporary change in the stream H2O ph toward basic during the cure… it’s really, REALLY hard to envision any environmental hazard the OP’s proposed activity could possibly introduce into the ecosystem. Comparatively, one would probably cause more harm to the Earth in driving to the library for the latest book on spiritual drumming. Relax. To the OP: Yes, it will work like a charm. As others have pointed out, concrete mix would be the best bet. Good luck with your quackers. Just be aware: What others have pointed out about State DNR or Federal Corps of Engineers regulations regarding creating impoundments is the real deal. They are very restrictive about modifying any “natural” flow of waterways. In your case however, simply creating a puddle for ducks to splash in would probably be viewed with a wink and a nod. (Unless you have a bitch for a neighbor that wants to make a Federal case out of it.) ---
**Author:** ![ZurBob](https://avatars.discourse-cdn.com/v4/letter/z/71e660/32.png) [@ZurBob](https://boards.straightdope.com/u/ZurBob)\ **Post date:** [December 15, 2018, 11:36pm UTC](https://boards.straightdope.com/t/using-bags-of-concrete-to-dam-a-small-stream/826158/15 "2018-12-15T23:36:34Z")
> [@Twoflower](#): > > I don’t know about Hawaii state laws, but as far as federal laws are concerned, your project is covered under the Clean Water Act. And, as long as you’re placing less than ten yards of fill below the high water line, you’re completely legal under [Nationwide Permit 18](https://usace.contentdm.oclc.org/utils/getfile/collection/p16021coll7/id/6711). Interesting. Thank you. ---
**Author:** ![boytyperanma](https://avatars.discourse-cdn.com/v4/letter/b/4491bb/32.png) [@boytyperanma](https://boards.straightdope.com/u/boytyperanma)\ **Post date:** [December 16, 2018, 12:49am UTC](https://boards.straightdope.com/t/using-bags-of-concrete-to-dam-a-small-stream/826158/16 "2018-12-16T00:49:56Z")
Keep in mind just creating a dam may not create the desired effect of a pond. The surround soil may just absorb the water or the water may find a different path. To create man made ponds they frequently use clays like bentonite to prevent water from perking out through the soil. I occasionally walk in a nearby town to a site called Ford’s Folly, Henry Ford built a 900ft long 30ft high dam to contain a stream running though the areas. The dam was completely ineffective in stopping the stream due to the porous bedrock below. ---
**Author:** ![nearwildheaven](https://avatars.discourse-cdn.com/v4/letter/n/90db22/32.png) [@nearwildheaven](https://boards.straightdope.com/u/nearwildheaven)\ **Post date:** [December 16, 2018, 1:00am UTC](https://boards.straightdope.com/t/using-bags-of-concrete-to-dam-a-small-stream/826158/17 "2018-12-16T01:00:29Z")
> **[Ford's Folly](https://www.atlasobscura.com/places/fords-folly-water-dam)** > > This dam in the woods, built by Henry Ford with only manpower and oxen, holds no water and serves no purpose. I live by a creek, and children in the neighborhood are always throwing rocks in the narrow areas in an attempt to dam it up. That doesn’t work very well. ---
**Author:** ![Mangosteen](https://avatars.discourse-cdn.com/v4/letter/m/6a8cbe/32.png) [@Mangosteen](https://boards.straightdope.com/u/Mangosteen)\ **Post date:** [December 16, 2018, 1:25am UTC](https://boards.straightdope.com/t/using-bags-of-concrete-to-dam-a-small-stream/826158/18 "2018-12-16T01:25:46Z")
> [@boytyperanma](#): > > Keep in mind just creating a dam may not create the desired effect of a pond. The surround soil may just absorb the water or the water may find a different path. To create man made ponds they frequently use clays like bentonite to prevent water from perking out through the soil. > > I occasionally walk in a nearby town to a site called Ford’s Folly, Henry Ford built a 900ft long 30ft high dam to contain a stream running though the areas. The dam was completely ineffective in stopping the stream due to the porous bedrock below. But where am I going to find Bentonite on the Big Island? Oh, that’s the entire island is made up of volcanic ash. Probably shouldn’t be too hard to find. Thanks! ---
**Author:** ![ZurBob](https://avatars.discourse-cdn.com/v4/letter/z/71e660/32.png) [@ZurBob](https://boards.straightdope.com/u/ZurBob)\ **Post date:** [December 16, 2018, 2:05am UTC](https://boards.straightdope.com/t/using-bags-of-concrete-to-dam-a-small-stream/826158/19 "2018-12-16T02:05:40Z")
Actually, old fashioned cat litter is Bentonite. I don’t get the impression that you’re trying to build a monument for the ages, so I think your plan will be fine for a few years. ---
**Author:** ![flurb](https://avatars.discourse-cdn.com/v4/letter/f/51bf81/32.png) [@flurb](https://boards.straightdope.com/u/flurb)\ **Post date:** [December 16, 2018, 2:30am UTC](https://boards.straightdope.com/t/using-bags-of-concrete-to-dam-a-small-stream/826158/20 "2018-12-16T02:30:54Z")
While the odds are (probably) small that you would suffer any consequences, messing with water channels without going through the proper hoops is a bad idea. Apparently, under [Hawaii Administrative Rules](http://blog.hawaii.edu/kahuliao/files/2018/04/HAR-13-169.pdf) any alteration to a stream channel requires a permit (page 12). And note what it has to say about penalties (page 4): \*Penalties. (a) Any person who violates any provision of this chapter or any permit condition or who fails to comply with any order of the commission may be subject to a fine imposed by the commission. Such fine shall not exceed $1,000 per violation. **For a continuing offense, each day’s continuance is a separate violation.** \* Your call, but considering that a permit filing fee is $25 you might want to think about your risk/reward ratio. [Next page](https://boards.straightdope.com/t/using-bags-of-concrete-to-dam-a-small-stream/826158.md?page=2)