Estimating irrigation demand

[sualac]

Does anyone know a reasonable demand factor (gpm/acre, gpm/edu??) for estimating irrigation demand for commercial, industrial, residential, parks, etc. I have found reasonable number for water consumption by using metering data but can't relate to irrigation demands. I suppose a peaking factor is what I am looking for. Any idea or theory?

 

[gerhardl]

Ask at the nearest agricultural university. Maybe someone there could help you.

I believe this will be depending on soiltype, plant and biotopic type, local climate (day/night temperature and humidity) and not at least how you distribute (drip type ground or spreader) and when (night/day), and of course max demand during dry periodes-

From your or your customers side it will also be an economic question: cost, operation and maintenance of equipment, capacity and cost of water.

Another possible approach: If your plants /biotope thrieves at, lets say 150 or 300 mm per square meter per month (just a figure) and you have cheap water available, you could also try to discuss if this distributed, say divided on each third night (just a figure again), is agricultural OK, and then check what this means equipmentwise.

You will also have to evaluate what selective areas have to be watered how much : native woods and plants would probably require nothing or perhaps only limited waterin during dry periodes, flowers or non-native plants more.

 

[sualac]

I understand your point but I am only doing general estimation of how much water will be used essential to pipe design. I do not know what will be planted but only the acreage of the parcel. I could assume a 1.7 gpm/acre for example but I do not have any backup sources for my decision. I hope am making sense.

 

[sam74]

I think it will depend on what type of fixture/sprinkler you use. There are a wide variety with differing areas of coverage. On the irrigation job I did for the most part I designed the whole system with a sprinkler I knew would do the job and then did a performance spec/drawing showing my caculated information. Just like a regular potable water calculation. The sprinkler manufacturer will have charts showing the radius of coverage at some given pressure. Get a hydrant test and model as such. I used EPANet.

 

[gerhardl]

OK. But you still have to go through the detailed planning way.

Looking into below link, you will get an idea of what area you can serve out of a 'normal' private garden system, through a normal hose(1/2").

If you assume this will be covered by 1-2 yards per second through the hose, you can establish a rough amount/area calculation.

You will still have to evaluate some of the details mentioned in my first posting,

http://www.gardena.co.uk/index.cfm?...rent_page_id=133&page_id=263&department_id=1&

 

[nackra]

http://www.rainbird.com/

their design manual was recommended to me to check an upcoming project. Cursory review looks like it has good basic information.

 

[BRIS]

My rule of thumb is one litre per second per hectare

In simple terms the typical crop water demand is approximately equal to the evaporation rate. (Ec =1)

Irrigation demand is (evaporation + losses) times percentage ground cover

Growing grass with an evaporation rate of 6mm/day at 80% efficiency (which is high) gives 0.9 l/sec/ha.