collecting rainwater 2

[cvg]

I'm looking at collecting rainwater and/or snow melt to be stored and used for replenishing a tank used for fire fighting. I have seen a system nearby which consists of a swale lined with hypalon which drains to a cistern. The water is pumped out, treated in a package plant and used for drinking water. For fire fighting, it wouldn't need to be potable so I am thinking possibly no filtration or treatment is needed. Anybody see any issues with this concept? How long would the hypalon last? Could cement or lime treatment be used to eliminate the need for the hypalon? Would the water need any kind of treatment?

 

[francesca]

I take it you have no roof drains to intercept?

 

[cvg]

no, this is for an airport in a very remote, arid region and the collection site would be between the runway and the taxiways. annual rainfall is in the range of about 12 inches per year. groundwater is probably unfeasible as it is 4,000 feet bgs to a productive aquifer

 

[DMcGrath]

I've seen a 15-year old scrim-reinforced Hypalon liner (30 mil I think) that was OK considering exposure to the elements. Physical damage (mainly puncture) was another story, however. You would probably want to provide a way to clean the sediment that would inevitably accrue in the cistern, and be able to limit the intake of sediment into the fire pump.

 

[cvg]

those were my thoughts exactly. Perhaps the liner could be covered with a layer of sand to protect it. Probably the only traffic would be the occasional maintenance vehicle, pedestrian or possibly a plane that might wander off the runway...

It could drain to a sort of french drain with perforated pipe and the sand would help to filter the water.

 

[nutter2612]

Have you considered using wastewater effluent ???

 

[cvg]

There is insufficient wastewater to fill the tanks. there is no potable water on the site.

 

[BarryEng]

In remote areas of Australia, we use a 'roaded catchment' for collection of rain water (in low rainfall agricultural areas) usually for farm dam supplies. The roaded catchment consists of a series of very shallow V shaped channels that are in parallel to each other (I hope that explains the situation).

The idea is that the runoff is immediate & there is very little time for the (rare) rain to soak into the soil.

One method of increasing the output, is to use 'catch drains' that intercept a larger area of catchment, & feed into the top end of the roaded catchment. But the output is much lower than an equivalent roaded catchment. This is used to enhance the flow at times of 'flash' rain showers.

I have not seen this type of catchment lined because (usually) it is only req'd for a farm (house) supply. Lining is usually only used for larger (potable) water sources. For a water utility, they used to line the catchment area with bitumen, but that's carcinogenic - so that is out, in this day & age. Hypalon has been used but be careful of wind damage & especially (as DMcGrath has pointed out) punctures & local damage.

In the general layout of a roaded catchment, the water flows into a silt trap before going into the farm dam. This just consists of a (relatively deep) local basin just before the farm dam storage. All it does is catch sediment such as sand, but it does not collect much of the fine silt or clay - that goes straight thru' to the dam storage.

Because of the fine fraction (clay) in the water, it does not clear even over many months. For fire fighting, it may be OK but to clear the water, you may require some settling agent. This is rarely done for farm dams because this is considered a second class water (for toilet flushing, gardens etc).

If you require, I can find more info on roaded catchments, however, the following (may be sufficient) is a google (for Oz) for roaded catchments - it may also work for overseas enquiries. The first reference is a very good start (from Western Australian Government Agric Dept).

[PDF] Bulletin 4660 : Roaded catchments to improve reliability of farm damsFile Format: PDF/Adobe Acrobat - View as HTML
Roaded catchments are easily constructed where there are duplex soils with ... These soils are normally satisfactory for roaded catchments if the depth to ...

http://www.agric.wa.gov.au/content/LWE/WATER/ENG/ROADEDCATCH_BULL.PDF

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Department of Agriculture, Western Australia : Roaded catchments ...A well constructed, well-maintained roaded catchment surveyed on the correct grade, constructed in suitable soil types can to begin to shed water after only ...

http://www.agric.wa.gov.au/pls/portal30/docs/FOLDER/IKMP/LWE/CLI/ADV/ROADCATCH.HTM

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[PDF] Increasing runoff from roaded catchments by chemical applicationFile Format: PDF/Adobe Acrobat - View as HTML
to roaded catchments. Funding was sought from GWRDC’s RITA program to test a .... To examine the performance of existing roaded catchments (additional aim). ...

http://www.gwrdc.com.au/downloads/ResearchTopics/RT 03-20-4.pdf

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Technology in Australia 1788-1988, Chapter 3, page 167The roaded catchment, (Fig. 8) claimed to be 'the greatest single advance in water conservation that has been made in this State' was conceived by ...

http://www.austehc.unimelb.edu.au/tia/167.html

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been using roaded catchments since the 1950s for town .... roaded catchment in WA, the average total cost would. be around A$500/ha, based on 1980 prices ...

http://www.catchment.crc.org.au/pdfs/technical200406.pdf

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[PDF] Miscellaneous publication 14/2005 : Roaded catchmentsFile Format: PDF/Adobe Acrobat - View as HTML
A roaded catchment is one of the water harvesting structures known ... Includes roaded catchments added to existing farm dams or planned as new roaded ...
ecohydrology.uwa.edu.au/__data/page/135534/Designing_Roaded_Catchments.pdf - Similar pages

VIC Country Hour - 30/08/2004: Roaded catchmentsThe "roaded catchment", as its called, is popular in Western Australia, and Ken West says even after light rain, there's pleanty of run-off into his dams. ...

http://www.abc.net.au/rural/vic/stories/s1188054.htm

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Maintaining Roaded Catchments ? September 2007 ... particularly roaded catchments, can dramatically ... Scraping the surface of roaded catchments with a ...
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[bimr]

It does not sound like a feasible concept.

You need to figure out how the fire fighters would use the water. If you were in a city, the hydrants would have to put out at least 1,500 gpm for 2 hours or so. That would be 180,000 gallons.

If you recover half of the annual rainfall, that would take about 60 acres of collection area. You would also have to worry about evaporation of the supply.

On the other hand, if you have such a small airport facility, the aiport may not even have hydrants. Small towns use pumper trucks to fill transport trucks with water. The ones that I have seen have used suction hoses to fill the the trucks from a reservoir for example.

Before spending too much time on this, I think the first step would be to discuss the fire fighting water needs with the airport fire department or a fire protection engineer. Airport hangers also have special fire fighting needs as well.

A small well filling a reservoir seems like a more reliable option, then depending on the gods for rain.

 

[KiwiMace]

Agree with BIMR - I don't think you will collect enough rain to warrant the cost of the installation.

Your scenario is highly intermittant rain supply, massive collection area requirements, and highly intermittant usage... knives that stab at the heart of feasibility. BarryEng describes much lower water demand applications, and less critical.

Your firewater tank needs to remain full at all times, so you need a separate storage tank and then pump into the FW tank to top up after any discharge.

Commercial rain collection systems dump a good percentage of the water due to grit and residues collected at the first rain.

Truck it in.

 

[cvg]

I think most have hit on the same issues that I have also.

airport is already existing with a tank, pump, waterlines and hydrants, so that is not an issue. Existing tank can handle a fire, however once it is empty it needs to be refilled as soon as possible.

area for catchment is large and 60 acres or more is probably available. Essentially, all the area between the runway and taxiways (the infield area) could be used to collect water. A small dry lake nearby might also be used. Water can also come from snow melt in addition to the occasional rainfall. The thought was to store it in a tank to eliminate evaporation, so that is not a problem. One idea I had was to construct a second tank. That way you could refill the empty tank with rainwater / snow melt intermittently while the other tank was already full. Or, if rainfall did not occur you could also truck water in and have a more redundant fire protection system. However, I agree that cost of constructing the collection system, desilting faciity etc. may be more costly than just trucking the water in.