Modeling Surface Water Temperature of a Pond

[jpreher]

Hi all,

I am currently working on a task which requires a decent model of evaporation rates from a pond. Water is deposited into the pond from a series of nozzles that spray droplets into the air over the pond. I have found some equations that I would like to use that model evaporation rates from the spray and standing water, however, to calculate the standing water evaporation I would like to model the surface water temperature to generate as accurate results as possible.

I plan to ignore the spray's effect on air temperature and relative humidity over the pond as the pond is a few acres in area, with the sprinklers taking up only a very small portion of this.

As the pond is only 4 feet deep I hope to ignore stratification of pond water layer temperatures.

Are there any models that utilize climatological data including wind speed, air temperature, relative humidity, etc. that could be used to model the surface water temperature of a pond?

 

[Shifty8]

Basicly you are asking for an meteorical model as used for predicting the weather, I doubt that's publicly available... I do remember NASA has some nice Models for calculating the surface temperatures of the oceans, but if I'm not mistaking these are based on satellite IR measurements.

For the sake of providing a useable answer, why is it you want to measure the evaporation rate of the pond? In other words, isn't there a different solution for the problem you're trying to solve?

Basicly I'm afraid any solution, given the fact you get all the equations together, is going to be far fetched from reality due to the immense complexity and the many variables such an equation derrives from. Wich should be a problem, since most of the variables are far from static... The weather is prediticable, to certain heights.

 

[jpreher]

Clarification:
I am not attempting to predict the weather, rather, I am trying to predict surface water temperatures of the pond based on collected climatological data (wind, humidity, etc.).

I have data that has been acquired from an area approx. 1 mile away from the pond (roughly same elevation). This data is collected every 20 seconds spanning back to January of 2004 and includes all values which should be relevant for determining anything about the air and climate conditions at a given time in the past.

Background:
I am trying to calculate water loss rate trends of this pond in an attempt to find current evaporation losses (instantaneous) and predict future loss as best possible based on past trends (or averages of my previously stated data).

This pond has had high water elevation problems in the past and I am attempting to account for how much water is actually lost to evaporation so that other measures can be properly used to regulate it from future problems (the only of which plausible at the moment would be a costly project of increasing the surface area of the pond, as only so much of the pond water may be released annually and the flow rate into the pond cannot be restricted.)

I have found a few places that say the water temperature should be lagged behind changes in climatalogical conditions but provide no equations or estimations.

 

[Shifty8]

I feel like I owe you a clarification as well, I'm not suggesting you are trying to predict the weather, I'm just pointing out that the evaporation rate of the pond is closely related to it. Espacially relative air humidity, which indicates how much water is absorbed by the air (look up the Mollier diagram for information) and thus how much water can still be absorbed, but also air density, height, air temperature, air pressure, additives in the water, water temperature and the distribution of the different temperature layers in the pond, wind speed, heck, if I'm not mistaken even the possition on the moon has some effect. In this aspect, it's much like trying to predict the weather, hence my comparison.

I understand your problem now though, looking at your previous post it seems to me we're talking about a pond of cooling water, like used by factories. Hence they may not release to much into the environment, so you need to even out the differences from evaporation, rain, and added water. Hence another solution would require a larger surface area, which allows for more water to evaporate.

That brings me to the next question, what was the reason of the high water levels in the past? Was it rain? Try to locate the deffinitive source, and then tackle it. Cause if so, not even providing a larger surface area would be a solution, since the pond would gather more water during rain. I'd recommend a buffer vessel to collect the excess pond water in case of lot's of rain (combined with a float and pump offcourse)

I'm sorry I can't help you with the a watersurface temperature model since I'm no expert on that at all, but I hope this post has helped at least a bit.

P.S. Yes, water temperatures also lag behind any change in air temperature, as long as were talking about a closed pond.

 

[jpreher]

Thanks for the suggestion, I will keep that in mind. However, I must do the calculation reguardless.

I already have equations that I would like to use for the evaporation that take into account most of the parameters mentioned by shifty8, my problem is as an input I require the water temperature at the surface of the pond. I figured that there should be an equation to calculate the temperature at the surface of the water without too much trouble.

I have all of that I believe I would need (all but the water temperature of course!) including:
wind speed / direction
radiation (W/m^2)
relative humidity
atmospheric pressure
air temperature
precipitation

Would anyone know of a good equation to estimate the temperature at the surface of the water?

 

[RTW69]

You might look into models for solar ponds. Most are salt ponds but they have been extensively studied. A good text such as "Solar Engineering of Thermal Process" Duffie and Beckman would be a good start. Also swimming pool heat loss analysis will have evaporative heat loss algorithms. Try a Google search on swimming pool heat loss.