Creek Flow Rate Calculation??

[TexasRed]

Trying to determing suitability for hydro system. Creek dimensions are approx 4'6" wide x 4'2" deep. (at this time) flow changes seasonally but not lesser by more than %20. so 54"w X 50"d = 2700 sq. in. X 12" = 32,400 cu.inch in a 1 foot cross section or 225 cu. ft in 1 inch cross section. I keep coming up with this math, but dosn't seem right to me. I marked off 10' length of the creek. Placed a fishing bobber in the creek and timed time of travel from start to finish. Time of travel was 8.4 sec average over 3 time trials. How can I figure volume per minute of the creek. What's the formula?

Second determination I need to make is engineering of head on creek. I live in east Texas. Fairly flat. From where the creek enters my property to where is leaves is a 3 foot head, I'm willing to invest 5 to 10 yrds concrete for dam to gain head, but still only looking at maybe 6 to 8 foot head max. Does this site have potiential for micro hydro usage?

[Countryboy]

Do a google search for a Weir gate.  That is how you calculate flow rate.

It is possible to get a rough guess by measuring stream width, depth, and then timing a floating object.  Is your stream perfectly squared, or do the sides gradually slope down to the 4'2" deep?  You have to factor in for that.

If there is only 3 feet of drop from where the creek enters your property to where it leaves your property, then you aren't going to get 6 to 8 feet of head by damming up the stream - unless you plan on flooding your neighbors property.

3 feet of head isn't much to work with, but it is something.

Banki/Mitchell turbines tend to be the best for low head situations.

A cubic foot is 1728 cubic inches, not 144 like you calculated.  If your stream is perfectly squared, 32,400/1728 is 18.75 cubic feet.

[TexasRed]

Thank You for the corrections. The creek is pretty square at the point of measurements, hence why I chose that spot. %80 of the creek bed is rock bottom, clean swept, hence flate w/no slope. I looked for the straightest 10foot section with paralell edges for measurement. My neighbors property is a bog/swamp that filters into a single channel creek at the start of my property line. Neighbor does not utilize this swamp for any purpose, and he was gracious to grant me duck hunting rights to that property. An extra couple foot of water to the swamp would help the duck habitat out. Added benifit to green power, hehe. I will look into the Banki/Mitchell turbines, but either way, I will need more head. Weir gate, I've seen some shallow versions. I'll look into it some more for a practical application to my situation. Thanks for your inputs and insight.

[RogerAS]

Texas,

Have you considered an undershot paddlewheel? Water has so much force one could gear up the rotaional speed to an alternator or PM DC motor easily. This would be a much more simple solution than building a dam, and if the neighbor sells out, dies or otherwise transfers ownership you have no loss of power. Considering the environmental sesitivity of wetlands some governemntal authority might have some "input" about that dam. An 8 spoked paddle wheel of strongly constructed could go several years between serious repair. Using a belt and pully system would also be very reliable and safe.

Just my $.02 worth.

[RP]

Well assuming 50" X 54" in a channel with straight sides then you have:

4.50' X 4.166' = 18.75 sqft

Multiplied by a 10' long section gives you 187.5cuft.

Since it takes 8.4 seconds to cover your ten feet you have:

187.5 / 8.4 = 22.32cuft/sec or X 60 = 1339cuft/min.

Hope this helps

[TexasRed]

I had not considered that approach. I was thinking along the lines of PM instead of alternator. I'm doing a box fan conversion at the moment for a learning exercise. The money I save on a dam adds all that much more to how efficient a system I can build. I'll look into undershot type paddle wheel system. Thank You.

[TexasRed]

Oowwwww, I got a headache just following along with that. Too early in the morning for that, hehe, I appreciate the use of your braincells greatly. Not sure I could have done that with out a few cold ones in me. Math is not a strong suit, English is my second language, I'm still looking for a first. Thanks.

[Slingshot]

Hi Texas,

I'm wondering, wouldn't flooding that swamp out more tend to reduce your flow rate?  My thought is that the surface area of the swamp would probably spread quite a bit on that flat land if you raised the water by 3 feet.  This would increase evaporation loss as well as percolation into the soil.  

Since you wouldn't be changing the amount of water coming into the swamp, the outflow would have to go down by the amount of increased evaporation and ground seepage.

Where are you in east Texas?  My former roommate is living on Lake Bob Sandlin.  Their water levels and creek flows have been extremely low the past couple of years.

[TexasRed]

I'm near Jacksonville. There is a spring fed lake that drain into the swamp to the north of my property. That swamp filters down for about 1/2 mile until it gets its act together and forms my creek. Last August, my pond was dry. The creek had 3 foot of water in it, and it was one of the worst dry spells I can remember. Hog hunting was good on my place during that time. Had lots of wildlife visiting me then. now my creek is back to running at normal depth. Had a small flood back around 1/15/07. creek went from 4 to 5 feet across to 50yrds wide, but that is a rarity. As far as raising the water level of the swamp, that was if I was to build a dam. I was thinking that with a dam, having an overflow, I could gain some more head. As mentioned before, and undershot wheel might be better. I kind of like that Idea, but I wouldn't be able to have it in a fixed postion, but like on a floating arm. To adjust for rise and drop. I don't know, things to ponder till summer, when I plan to start this project. Too cold now. Heck, our high temp was 50 yesterday, don't know if I can handle too many more of them cold snaps, can't wait till we get back to those 105 degree days. Thanks for your insight.

[Gordy]

BBrrrrrr,

TOO COLD, high of only 50. Ha come up to Minnesota, I'm 50 miles west of Minniapolis and had a high of 5 yesterday and 3 today. Saterday and Sunday are supose to be highs of -3. I don't have a wind chill chart handy, but TV said exposed skin can freeze in 10 mineuts with our 10-15 mph winds.

Gordy

[Nando]

Ok What is then your language, to see if it is easier in Spanish or the metric system.

22. 32cuft/sec = 0.632 M^3/s
    
3. feet = 0.914 meter
   
   

Available power is 0.632 * 0.914 * 6 = 3.5 KW

An undershot wheel may not be able to harvest all the power, may be 40 %, but a Banki or a Propeller may be able to harvest up to 60 - 70 % of the above calculated value, this due to the low head.

Nando