Depth change in lakes and ponds: easy monitoring solutions

By Ray Valley

Aquatic Biologist and BioBase Product Expert

One of BioBase’s strengths is its simplicity. You don’t need an advanced engineering degree in hydrography to make a high quality bathymetric map with an off-the-shelf sonar device. If you have your transducer installed correctly, settings correct on your Lowrance, and achieve good coverage on your waterbody of interest, then BioBase’s EcoSound algorithm will produce a very precise, high quality bathymetric map output within minutes of upload to biobasemaps.com. The speed and ease of bathymetric mapping wins the day for many of our users, but perhaps even more valuable, is the benchmark you are setting for an unknown day in the future when something has changed on the lake and you need to have some “historical” information to understand how much change has taken place

Use Case: Monitoring Sedimentation

One of our most frequently asked questions by new users is “will BioBase measure sediment thickness or the depth of the sludge?” This was a source of a recent blog. Interestingly, the answer is different depending on how long our customers have been using BioBase. For the user who has no prior information about how deep the lake or pond is supposed to be, BioBase may not provide detailed enough information about the actual thickness of the sediment (sediment depth is correlated with EcoSound hardness but it is highly variable; see this blog for further details).  However, for the pond management consultant who happened to “BioBase” a client’s pond in 2013 while she happened to be on site for another matter and is now hearing from the client in 2019 that his pond is “filling in,” the answer about whether BioBase can tell him how much sediment has filled in is a most definite yes! For this pond consultant, it was a most fortuitous (or perhaps prudent?) thing that she decided to voluntarily map her clients pond in 2013.  Now with a 2019 survey, she can precisely quantify exactly how much sediment has accumulated and where over the 7 years by doing a simple subtraction of the depth and water volume between surveys and comparing maps.  The comparison of maps can be done a fancy GIS way like described in this blog. Or a quick and easy way through BioBase (see examples below).

Sedimentation in Arizona’s Aqueducts – BioBase monitoring by Central Arizona Project

Delivering clean water to residences and businesses is a pretty big deal in Arizona. It’s a mostly a desert after all.  The Central Arizona Project manages 336 miles of aqueducts, tunnels, and pipelines and the desert dust seems to regularly find its way into the canals and rest in the forebays where water is pumped to the next stop along the network. Since 2012, BioBase has provided a very rapid, precise, and cost-effective tool for CAP for the monitoring sedimentation in 15 forebays. BioBase’s polygon tool is a very quick and accurate way of determining water volume (Figures 1 and 2).

Create a polygon
Figure 1. To generate water volumes, create a polygon around an area of interest. In this case, Salt Gila Forebay

Save the polygon and inspect statistics

Polygon Volume
Figure 2. Save the polygon around the survey area.  BioBase summarizes and displays only the bathymetric statistics in the polygon area. Jot down the relevant statistics in your tracking spreadsheet or export the polygon and the statistics come along.

I asked Central Arizona Water Conservation District (CAWCD) Senior Biologist Scott Bryan to share more about the history of monitoring these forebays and how BioBase is facilitating this important CAP program: “Prior to 2013, Central Arizona Water Conservation District (CAWCD) last conducted bathymetric survey in 2004 and 2005 to determine sediment levels in the CAP canal. Although the data gathered during this effort was valuable in determining the need for a sediment management program in the canal, the $100,000 price tag to complete the surveys in each of the 15 pumping plants was determined to be excessive and no additional surveys were completed. In 2012, I was tasked with revisiting the sediment management program. To adequately determine where sediment deposition was occurring, up-to-date surveys were necessary. I began to work with BioBase in 2012 to see if mapping using the Lowrance Chart Plotter and the cloud-based service would give an accurate representation of the sediment in the canal. A bathymetric map generated using BioBase was compared to baseline data from more expensive, time-consuming survey techniques. It was determined that BioBase matched up very closely with the baseline surveys. With that, CAWCD began an annual sediment mapping survey in 2013 utilizing BioBase. Now in it’s seventh year, the long-term data set has become the backbone of the sediment management program, as decisions for sediment removal are based, in large-part, on the results of the mapping efforts. In addition to the hundreds of thousands of dollars saved by utilizing BioBase over a contractor, mapping all 15 forebays takes just three days and maps are created nearly instantaneously.

See the change!

Salt Gila Forebay 2013-04-22
Figure 3. Salt Gila Forebay in April 2013. Central Arizona Project estimates from BioBase indicate sediment volumes of 19,300 yards occupying 32% of the Forebay’s volume
Salt Gila Forebay 2013-12-18
Figure 4. Dredging project implemented in December 2013 on Salt Gila Forebay. Survey completed shortly after and found 9,220 yards less of sediment than in April 2013. Sediment comprised 16.8% of the forebay volume after dredging.
Salt Gila Forebay 2018-04-17
Figure 5. Sediment in Salt Gila Forebay in 2018 was highest measured since 2004 and today occupies 36% of the of the forebay’s watervolume.   

To learn more about BioBase contact us at info.biobase@navico.com.

Author: biobasemaps

BioBase is a cloud platform for the automated mapping of aquatic habitats (lakes, rivers, ponds, coasts). Standard algorithms process sonar datafiles (EcoSound) and high resolution satellite imagery (EcoSat). Depth and vegetation maps and data reports are rapidly created and stored in a private cloud account for analysis, and sharing. This blog highlights a range of internal and external research, frequently asked questions, feature descriptions and highlights, tips and tricks, and photo galleries.

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