Visualize for a moment a square mile of land covered by a layer of wet silt 14 feet thick. That’s how much accumulated silt is choking the life out of 85-year-old White Rock Lake.
The City is now working on plans to remove some of that silt in an $18 million dredging project. The big question is whether the City’s project will really make much of a difference.
White Rock Lake was formed in 1911 with a storage capacity of 18,158 acre feet. Siltation has reduced its capacity to less than 9,000 acre feet. Silt has drained into the lake, primarily by way of White Rock Creek, from decades of natural forces, erosion, and soil displacement stemming from rapid urban development in North Dallas and Collin County.
The goal of the dredging project is to remove an estimated three million cubic yards of silt to achieve a minimum depth of eight feet. City engineers plan to use a floating hydraulic dredge to cut up the silt and pump it out of the lake. Dredging is expected to take two years and should be completed in the summer of 1999 or 2000, depending on whether a three- or four-year bond program is adopted.
A couple of points about the dredging plan bear mentioning: First, don’t get the idea that White Rock Lake is going to be scraped clean of muck. Three million cubic yards equals only 20 percent of the accumulated silt. And only the northern third of the lake will be dredged, while the remainder of the lake won’t be addressed.
Second, the City’s plans do not yet – and may never – address long-term, upstream measures, such as retention basins and erosion controls, to reduce the amount of silt flowing into the lake.
By the City’s own estimate, the silt expected to be removed under the current plan will be re-deposited in about 20 years. The north end of the lake would likely again be off-limits to boaters and fishermen well before that time.
The City’s consulting engineers will be providing specifications for a small dredge, which the City could buy and use at White Rock Lake and other City lakes to remove silt. Of course, the cost of using the dredge and disposing of the silt will be subject to the political whims of future City Councils in the annual City Hall budget melee.
Given the Council’s past orphan-child treatment of the Park and Recreation Department, which would operate the dredge, we shouldn’t hold much hope for a dredging program that can keep up with the rate of siltation.
Disposal of the dredged silt remains a major issue. Current plans call for silt and water to be pumped directly from the lake through the City in above-ground pipes and deposited on undeveloped tracts of land in Dallas.
The City Public Works Department has come up with a candidate list of 76 tracts for disposal; the list will be narrowed to about 20. The sites range from one to eight miles from the lake. In our neighborhood, Flagpole Hill is on the list as a potential reclamation site. One imaginative Dallasite has suggested using the silt to build a brand new hill hear the lake (“ski Dallas” anyone?). Having to use more remote sites could raise disposal costs beyond current estimates, possibly resulting in less silt being removed.
The City Council will choose the silt disposal sites next year, and the selection process could become political, with several Council districts having proposed disposal sites. Many of the proposed sites are south of I-30, and grumblings about North Dallas imperialism in the selection process already have been heard.
Although tests of the silt have indicated no dangerous levels of chemicals, and City engineers promise the stuff won’t stink, residents near proposed sites might adopt a not-in-my-backyard attitude toward silt disposal.
Stay tuned on this issue.
