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1
Small Dam RepairThe Stone Lake Dam Story
Joe Barron, P.E.SynTerra formerly the Fletcher Group, Inc.148 River St. Suite 220Greenville, S.C. 29601
2
Historical background of Stone Lake
A series of three lakes built by the Stone family in the 1960’s
Development of subdivision in City of Greenville, SC
Built roads over dams –dam belongs to Home Owners Association, roads to City
4
Experience with State Park dams
Table Rock State Park DamOld CCC dam for mountain lake 60 feet high with internal spillway gate leaking. Couldn’t lower lake because of Legislative conference.
Santee State Park Dam: lowcountry farm pond size dam with leaking gate. Couldn’t drain because of backwater from hydro reservoir. Put on Scuba to remove old gate.
5
Notification of Problem Inspection by South
Carolina Department of Health and Environmental Control (DHEC) noted problems in the spillway
7
Terms
Spillway refers to the 48 inch concrete pipe primary spillwayDrain refers to the 12 inch steel pipe drain
for the lake
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Spillway A brick and concrete spillway
controlled the water level of the lake and then drained to the spillway pipe
10
Condition of pipe interior
Note the water coming through the pipe disappears about 3 joints up the pipe and comes out under the pipe
A catch basin in the street above appeared to be bearing on the pipe
13
Additional concerns
A street culvert that used to discharge into the spillway pipe and was later diverted to discharge below the dam
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Additional problems Steep slopes, hard to walk
on, much less maintain Tree growth and root
system weakens dam
16
Lake drain pipeConcern over the 12
inch diameter pipe under the dam used to drain the lake
Could not find the endWater spilling out
around some tree roots
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Options
Just seal the joints on the main overflow drain and dig out the end of the drain and keep watching the dam
Take the opportunity to remove the trees, reslope the dam, rebuild the overflow spillway, and study the hidden drain for possible repairs
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The plan
The City and Homeowners Association opted for the more expensive route believing that a band aid was not adequate and that more extensive problems might be uncovered during the work
19
Hydrology and Hydraulics Suburban watershed
with two lakes upstream
Recently studied by City consultant
Concluded that spillway pipe was correctly sized
20
Characteristics of dam
12 inch diameter.Size of Drain48 inch diameterSize of Primary Spillway
85 feetLength of Primary Spillway250 feetLength at top125 feetWidth at bottom45 feetWidth at top30 feetHeight
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The battle plan
Add a new junction box at the location of the disjointed spillway pipeThe spillway will turn at this point and
discharge at a lower point to allow the most serious area of downstream erosion to be filled and grassed
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The battle plan
Cut all trees, remove stumps and reslope the back of damClear end of drain and inspect with videoPlace toe drain of stone wrapped in filter
fabric to catch seepage under dam
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Changes to recommendations on drains & filters
Prior to the 1980’s seepage collars were recommended and in some cases required around the piped drains through dams
Starting then a number of studies indicated that seepage collars were not working due to the difficulty of compaction around them
Pipe filters of sand and stone are now recommended
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Challenges and solutions 1 More seepage than
anticipated, but all under the dam, not through it
Revise Toe filter to utilize a sand and stone filter
Add a monitoring point
34
Challenges & Solutions 2 Significant root
systemsAnticipatedEncouraged that no
seepage was noted around the roots
35
Challenges and solutions 3
Spillway pipe crumbled when removed, not reinforced, raised concern for pipe left in place. Dig and replace or slipline?Dig up and replace would mean redoing the
road and replacing pipe that did not appear to have seepage problems around it.
36
Sliplining optionsSmooth core aluminum pipe to slide inside 48” –
problem concrete pipe is not completely round and joints are not even
Use resin impregnated fabric to seal the pipe –would not provide any structure or strength but would eliminate seepage – City had Insituformcompany under contract to slipline sanitary sewer
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Challenges and solutions 4
Drain under dam was uncovered, inspected with video, proved to be in bad shapeDecided to plug with flowable fillAdd siphon drain over dam, under road
instead of through dam
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Challenges and solutions 4
Drain under dam was uncovered, inspected with video, proved to be in bad shapeDecided to plug with flowable fillAdd siphon drain over dam, under road
instead of through dam