DOBSON RANCH LAKES 2024 SEDIMENT STUDY

by Zach Hache, Water Resource Manager

Aquatic Consulting and Testing, Inc. (AC&T) recently completed a sediment study of the lakes at Dobson Ranch. Similar studies were completed in 2003 and 2014 and are beginning to provide important information regarding the sediment accumulation rate, deposition patterns, and compaction within the lakes. Sediment studies are an essential component of lake management for several reasons.

First, as sediment accumulates in the lake basins, the lake bottom gets closer to the water’s surface, rendering more of the lake area exposed to sunlight and susceptible to aquatic weed and filamentous algae growth. Sediment accumulation occurs naturally, and the rate of sediment accumulation can change. Factors that can increase the rate of accumulation include

• Runoff of dirt from the shoreline into the lake, primarily where the shoreline is steeply graded

• Algae and aquatic weed blooms and decay

• Natural aerial deposition from dust storms and other weather events

Understanding the extent and pattern of sediment deposition in the lake provides insight into modifying or regulating some listed factors.

Second, lake sediments contain ample amounts of nitrogen and phosphorus (plant nutrients) that promote the growth of aquatic weeds and planktonic algae. Sediment studies can determine the location and concentration of nutrients and help determine the need for remedial activities and potential uses or disposal options for the material. Finally, and potentially the most critical, sediment studies allow for the determination of when the lakes may need to be dredged. Dredging activities can be very costly, both monetarily and in terms of disruption to the community around the lake. Proper planning can allow reserve planning and activities to minimize public disruption.

Sediment removal is typically accomplished in two ways: either draining the lake, allowing the sediment to dry, and removing it with mechanical equipment, or utilizing a suction dredge and dewatering bags. Suction dredging allows the lake to remain full and selectively addresses the areas with the greatest sediment accumulation. Dewatering the sediment onsite also allows for much lower transport costs of the dried material to a landfill or other disposal site.

Although the 2024 sediment survey results show that most of the community’s lakes will not require dredging tomorrow, there is a need to start planning for the future dredging of Lake 3 in about five years. These results are available to the community on the website under the Amenities tab, then click Lakes. For more information, please attend the monthly Water & Lake Management Committee meeting held at La Casita Recreation Center on the second Tuesday of each month at 5:30 p.m.