Dear Given Dave Paquiding Layos

Hi

I think the follow the below link maybe is useful for you!

https://web.ics.purdue.edu/~vmerwade/reports/2018_01.pdf

https://www.researchgate.net/topic/HEC-HMS

https://www.napier.govt.nz/assets/Documents/District-Plan-Change-12/District-Plan-Change-12-2nd-tranche/10B-TT-Mission-Special-Character-Zone-Flood-Effects-Assessment-Updated-April-2018.pdf

https://www.hydrol-earth-syst-sci.net/18/5289/2014/hess-18-5289-2014.pdf

Best Regards

Hi Zeinab! Thank you for these helpful resources!

The question is a good one. Usually when someone asks about the design storm for a dam or pond, they are referring to what size of overflow relief channel will be needed to avoid failure. Perhaps HEC HMS can tackle this type question, but what you may want to know so your pond has water, even in dry periods, is what is the minimum or low rainfall common to your area, during dry periods, does the contributing stream still flow, how much minimum flow to expect, how much is the evaporation from a pond each year, how much does the watershed vegetation use in transpiration, and how much do you intend to use, and perhaps the minimum needed in case of using drought numbers. How much does the soil leak to groundwater. Hydrologists and water managers call this a water balance. You can estimate dry, average or wet year water balance numbers, and you might find data from any meteorological and stream gauging stations within you vicinity or physiographic area. Soil maps may also help. The drainage area of the watershed is often an important factor in these calculations. There is an old book on Design of Small Dams that may be helpful (on internet). One must recognize that in taking all or much of the water will cause some downstream effects to aquatic organisms and neighbors, who may also need water. You will want to know if you need to seal off the pond bottom with clay if there is not a good clay layer to help hold water. Some countries may want you to obtain a construction or water use permit, or provide a design plan as you are considering. Local farmers or farm agencies can sometimes help. Often those who have ponds or dams are expected to manage and maintain them properly, so they do not provide a downstream source for invasive species, become overwhelmed with algae, or do not fail during flood and cause downstream damage that owner might be liable for. So if the small pond graduates to larger size, it is probably worthwhile to have a licensed engineer approve plans to help with the liability issues. If you wanted to select a design storm that would occur most years to fill your pond, probably the bankfull storm that occurs about every 1.5 years might be acceptable, but recognize in a dry year, you may or may not have a bankfull storm event. You would not use this storm to construct an overflow channel. In my researchgate list for 2013, there is a paper discussing the efforts to remove a small dam from the National Forest to avoid failure, you might find that interesting.

Thank you Sir William Hansen for these insights. I would like to clarify though to what parameter should I base the sizing of water harvesting ponds. Should it be based on a design storm or in the actual water that maybe harvested calculated from the water balance? I am to design a water harvesting pond for non-potable application. I am hoping for your response sir. Thanks!