Among the many parameters that we are measuring on a continuous basis in our restored marsh, we have measured the Colored or Chromophoric Dissolved Organic Matter (CDOM) using a Turner design sensor. Below, you can view the dynamics of CDOM as a function of flow and stage. The CDOM concentration values are only relative as calibration against Quinine Sulfate Equivalence has not been applied on this data. There are many things to say about these data. For today, I just let you enjoy the view and think about it!
Wednesday, May 23, 2012
Dissolved Organic Matter fluorescence dynamics in our restored coastal marsh
by François Birgand
Among the many parameters that we are measuring on a continuous basis in our restored marsh, we have measured the Colored or Chromophoric Dissolved Organic Matter (CDOM) using a Turner design sensor. Below, you can view the dynamics of CDOM as a function of flow and stage. The CDOM concentration values are only relative as calibration against Quinine Sulfate Equivalence has not been applied on this data. There are many things to say about these data. For today, I just let you enjoy the view and think about it!
Among the many parameters that we are measuring on a continuous basis in our restored marsh, we have measured the Colored or Chromophoric Dissolved Organic Matter (CDOM) using a Turner design sensor. Below, you can view the dynamics of CDOM as a function of flow and stage. The CDOM concentration values are only relative as calibration against Quinine Sulfate Equivalence has not been applied on this data. There are many things to say about these data. For today, I just let you enjoy the view and think about it!
Friday, April 20, 2012
Illustrating flow proportional sampling
by François Birgand
One of our domains of expertise is the computation of uncertainties on nutrient loads at the outlet of watersheds. We have published several articles on the subject and will be presenting some more results at the ASABE conference in Dallas, TX at the end of July. One of them will be the evaluation of the flow proportional sampling method to calculate nutrient loads.
This methods consists in automatically sampling and compositing the samples into one big bottle (usually around 20 L). The nutrient or material load can be calculated by multiplying the composite concentration by the flow volume corresponding to the period during which the samples were taken. This system can be set up to measure the nutrient load for just one storm, or set up to measure loads on a longer term basis, including annual periods. In the latter case, the system is set so that samples are composited over a period corresponding to two consecutive field servicing times. The system requires an automatic sampler connected to a flow calculating device. This device computes flow rates and calculates the flow volume accumulated since the last sample. When the cumulative volume reaches a defined threshold, the device triggers the sampling, usually of a small volume.
The first point we want to illustrate, is the concept of cumulative flow. Cumulative flow over a given period is the integral under the hydrograph over the same period. This is illustrated in the video above. Instantaneous flow rates (hydrograph) are represented in the thin blue line while the cumulative flow volume (in mm) is represented both by the area under the hydrograph and the thick blue line. The triggering of a sample can thus take place after e.g. 0.5 mm has flowed by.
Lots of hydrologists use the flow proportional composite method, and we believe for the right reasons. We have noticed that to explain how it works, it often involves hand waving and other less than ideal artifices. For that reason, we have decided to create an illustration in the form of a video, which we hope will provide some help. Ideally, this video will be used by others in the future.
The video shows the same hydrograph as before and a red dot travels through time. The vertical bars mark the times at which the sampler is triggered and the water accumulated is illustrated in the bottle. Notice, and that is the heart of the method here, that the sampler is triggered a lot more often during high flows. One can show that the concentration in the composite bottle is a very good approximation of the flow weighted concentration over the same period of time, which warrants the use of this method to calculate nutrient and material loads. There are cases, and in particular for suspended solids where this method may induce some significant error, although much smaller than for any other methods. This will be discussed at length this summer.
One of our domains of expertise is the computation of uncertainties on nutrient loads at the outlet of watersheds. We have published several articles on the subject and will be presenting some more results at the ASABE conference in Dallas, TX at the end of July. One of them will be the evaluation of the flow proportional sampling method to calculate nutrient loads.
This methods consists in automatically sampling and compositing the samples into one big bottle (usually around 20 L). The nutrient or material load can be calculated by multiplying the composite concentration by the flow volume corresponding to the period during which the samples were taken. This system can be set up to measure the nutrient load for just one storm, or set up to measure loads on a longer term basis, including annual periods. In the latter case, the system is set so that samples are composited over a period corresponding to two consecutive field servicing times. The system requires an automatic sampler connected to a flow calculating device. This device computes flow rates and calculates the flow volume accumulated since the last sample. When the cumulative volume reaches a defined threshold, the device triggers the sampling, usually of a small volume.
The first point we want to illustrate, is the concept of cumulative flow. Cumulative flow over a given period is the integral under the hydrograph over the same period. This is illustrated in the video above. Instantaneous flow rates (hydrograph) are represented in the thin blue line while the cumulative flow volume (in mm) is represented both by the area under the hydrograph and the thick blue line. The triggering of a sample can thus take place after e.g. 0.5 mm has flowed by.
The video shows the same hydrograph as before and a red dot travels through time. The vertical bars mark the times at which the sampler is triggered and the water accumulated is illustrated in the bottle. Notice, and that is the heart of the method here, that the sampler is triggered a lot more often during high flows. One can show that the concentration in the composite bottle is a very good approximation of the flow weighted concentration over the same period of time, which warrants the use of this method to calculate nutrient and material loads. There are cases, and in particular for suspended solids where this method may induce some significant error, although much smaller than for any other methods. This will be discussed at length this summer.
Wednesday, April 18, 2012
Displaying our innovations
by François Birgand
The College of Agricultural and Life Sciences (CALS) at NC State was hosting a conference: "Stewards of the future: Research for Human Health and Global Sustainability". Along with the conference, CALS hosted its Innovation Fair, where our team had two booths. We are firm believers that new discoveries will come with news ways of obtaining data, and in particular will come from high time resolution data. We decided to show our latest innovation in this field.
Randall Etheridge (Ph.D. student) and Brad Smith (Research Assistant - left and middle on the picture above) manned the booth entitled 'Capturing the perpetually changing world of a tidal marsh'. A live demonstration of our multiplexer pumping system to measure water quality on a high frequency basis for up to 12 sources was displayed along with a poster and a slide show presenting preliminary results from our study coastal marsh near Beaufort, NC.
I manned the GaugeCam innovation booth entitled 'Hydrology for all: measuring water level using webcams'. This booth had posters, videos, a slide show of how the system works and of results, live data streaming from the field and a display of the GaugeCam hardware.
Overall, we got some good feed back from the few people that did stop by. I really think our presentations were very interactive and were among the better ones for that. We did not capture enough interest though but we learned a lot from that nonetheless. One day, all this will pay off!
The College of Agricultural and Life Sciences (CALS) at NC State was hosting a conference: "Stewards of the future: Research for Human Health and Global Sustainability". Along with the conference, CALS hosted its Innovation Fair, where our team had two booths. We are firm believers that new discoveries will come with news ways of obtaining data, and in particular will come from high time resolution data. We decided to show our latest innovation in this field.
Randall Etheridge (Ph.D. student) and Brad Smith (Research Assistant - left and middle on the picture above) manned the booth entitled 'Capturing the perpetually changing world of a tidal marsh'. A live demonstration of our multiplexer pumping system to measure water quality on a high frequency basis for up to 12 sources was displayed along with a poster and a slide show presenting preliminary results from our study coastal marsh near Beaufort, NC.
I manned the GaugeCam innovation booth entitled 'Hydrology for all: measuring water level using webcams'. This booth had posters, videos, a slide show of how the system works and of results, live data streaming from the field and a display of the GaugeCam hardware.
Overall, we got some good feed back from the few people that did stop by. I really think our presentations were very interactive and were among the better ones for that. We did not capture enough interest though but we learned a lot from that nonetheless. One day, all this will pay off!
Tuesday, April 10, 2012
Flow, velocity and tidal harmonics in a restored coastal marsh
By François Birgand and Randall Etheridge
The goal of this post is to provide some fascinating flow patterns we have observed in a restored marsh where we evaluate the ability to dissipate excess nutrients coming from adjacent agricultural lands. You may find our latest results here presented at the NC WRRI conference in March 2012. You may also visit the site dedicated to the marsh results.
In the video below, you will see the flow and velocity patterns observed in November 2011 at the upstream station. The tidal fluctuations are represented in the middle by rising and falling rectangles. Flow is represented on the left. Positive flow represents ebbing tide (water penetrates in the marsh coming from upstream agricultural land) and negative flow, flowing tide. You may observe that there are no two same tides and tidal cycles. Water quality parameters and concentrations also vary dramatically. Another blog will be published on that subject.
It is particularly interesting to see a very peculiar pattern at high tide where flow can suddenly be inverted, which induce 8 shape curves. This is due to the existence of a flow loop in the marsh.
At the downstream station, the tidal harmonics exhibit a more expected behavior. Watch for the differences in the flow and velocity scales.
This needs to be accompanied by the water quality analyses, but we thought we should post this now for your enjoyment!
The goal of this post is to provide some fascinating flow patterns we have observed in a restored marsh where we evaluate the ability to dissipate excess nutrients coming from adjacent agricultural lands. You may find our latest results here presented at the NC WRRI conference in March 2012. You may also visit the site dedicated to the marsh results.
In the video below, you will see the flow and velocity patterns observed in November 2011 at the upstream station. The tidal fluctuations are represented in the middle by rising and falling rectangles. Flow is represented on the left. Positive flow represents ebbing tide (water penetrates in the marsh coming from upstream agricultural land) and negative flow, flowing tide. You may observe that there are no two same tides and tidal cycles. Water quality parameters and concentrations also vary dramatically. Another blog will be published on that subject.
It is particularly interesting to see a very peculiar pattern at high tide where flow can suddenly be inverted, which induce 8 shape curves. This is due to the existence of a flow loop in the marsh.
At the downstream station, the tidal harmonics exhibit a more expected behavior. Watch for the differences in the flow and velocity scales.
This needs to be accompanied by the water quality analyses, but we thought we should post this now for your enjoyment!
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