Hello, I have created a SWAT model in a basin where flow data does not exist. There are few water quality measurements: less than 10 measurements each for years 2013 and 2016 only, with 2013 data from July to October and 2016 data from September to December. Am I even able to calibrate and validate this model? How can I compare model outputs with my water quality nutrient data? Also, how can I compare SWAT outputs with my water quality nutrient data? Much guidance needed, thanks.
If you are conducting in North Carolina, there are numerous stream gauging stations in each of the physiographic areas and varying in drainage size, land use, etc. Some of these may also have some water quality data. I would consult with USGS website or personnel, and also NC Dept of Environmental Management to see if there are ways you might evaluate model function. There are a number of hydrology and water quality studies In this state, various agencies including US Forest Service and Universities. There are a number of hydrology researchers familiar with and publishing on SWAT, so you would do well to have their advice.
If you research is elsewhere, try to find other data within the physiographic area, climatic zone, topography, etc. validating with scarce data is probably not something you would want to hang your professional hat on.
If for example, you are in the piedmont, and have an average annual water yield of 15 inches of flow. If the drainage area is 100 acres, then the annual average water yield is 125 acre feet, which can be converted to gallons or liters. If you have a mean concentration you want to check out, 0.5 mg/l nitrate, and you have 125 ac ft times 1233480 liters/ac ft, or rounding, 154,000,000 liters in an average year. There is a million mg per kg. So if you knew the mean nitrate concentration to be 0.5 mg/l times 154 million liters = 77 kg nitrate if I did my math and converting units right.
The problem with water quality is it is somewhat flow dependent, can have some seasonality, and rainfall, discharge rate and land use are among factors affecting nitrates. If you do the unit conversions enough, the conversions to desired units becomes easier. For many water quality factors, you will want to sample changes through the hydrograph event, during rising stage, peak, falling stage and baseflow.
Hi
As you know calibration is a difficult issue especially in ungauged or data sparse regions. New studies in this field show that you can use satellite based datasets for calibration of hydrological models like SWAT.
You can predict stream flow by calibrating simulated soil moisture and remote sensing based soil moisture products such as SMOS, ASCAT.
In other words by calibrating soil moisture you can simulate stream flow accurately. I attached some new papers for you in this field..
I hope that works
the best
Azizian