Sediment and Nutrient Loads

SedEvent is an event-driven, automatic grab sampling system that provides a simple and practical method of accurately determining suspended sediment and nutrient loads. While suspended sediment concentration (SSC) cannot be directly measured accurately or reliably, turbidity has been shown to be an excellent surrogate for SSC. Turbidity is caused by suspended particulate matter such as clay, silt, algae, organic and inorganic chemicals and acids like fertilizers, and microscopic organisms like harmful bacteria. These contents give water its cloudy or turbid appearance, and turbidity in natural waters is recognized as an important indicator of natural health. Measuring suspended sediment concentrations used to be labor-intensive, costly, inaccurate and impractical. SedEvent not only makes it possible and practical, it makes it simple.


We didn’t invent the concept of Turbidity Threshold Sampling (that distinction goes to Rand Eads and Jack Lewis of the USDA Forest Service). But we did invent the concept of a turn-key system that uses this effective method of intelligent, automated grab sampling that requires no programming to install and maintain.

The ability to collect useful data about sediment transport and other pollutants closely coupled to SSC (such as nutrients, e-coli, phosphates and nitrates) is dependent on the timing and frequency of manual grab samples during run-off events. Most sediment and pollutant is transported during a small number of storm events which are infrequent and unpredictable. When they do occur, trained personnel or the proper equipment may not be available to collect grab samples. Manual grab sampling schemes are also labor-intensive, inefficient, dangerous and costly (and aren’t done 24/7/365).

An automated pump sampler can eliminate the need to sample manually, but for the expense of a rechargeable power system, the autosampler, and possibly a datalogger and a typical turbidity probe (which is often “noisy” and can trigger many unneces- sary samples), you’re no better off. The primary limiting factor is the number of sample bottles. By the time the autosampler is full, the probability that any sample will have been taken during the critical point of a storm event is low. Expensive lab analysis costs are likely wasted.

Neither method provides adequate information to make credible suspended sediment load estimates.

With an automated pump sampler driven by the DTS-12 digital turbidity sensor and controlled by the Axiom H2 datalogger, you obtain a better understanding of the water’s quality, while taking a minimum number of samples, reducing site visits and saving lab analysis costs.

The graph below illustrates three rain-driven events and the associated data recorded by a SedEvent system. The DTS-12 digital turbidity sensor monitors the turbidity of the water constantly. All measurements are recorded in the Axiom datalogger, which controls the attached automated pump sampler to take samples when it detects a rise or fall in turbidity at configurable thresholds.
The result is a series of water samples, intelligently taken—only during an event, when the water’s turbidity is high. Site visits are required only when the pump sampler is at capacity (which can be determined remotely via optional telemetry or scheduled for after known storm activity), and lab analysis costs are minimized as every sample counts.

Read More>