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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

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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

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Middle and upperStone Lake Dams

Lower Stone Lake Dam – the project site

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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.

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Notification of Problem Inspection by South

Carolina Department of Health and Environmental Control (DHEC) noted problems in the spillway

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Dam Classification “High Hazard” by

DHEC Significant property

damage with downstream flooding

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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

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Cracking was noted in the spillway apron

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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

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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

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Down stream erosion

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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

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Hydrology and Hydraulics Suburban watershed

with two lakes upstream

Recently studied by City consultant

Concluded that spillway pipe was correctly sized

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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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Construction Begins

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Clearing and Grubbing

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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

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Challenges & Solutions 2 Significant root

systemsAnticipatedEncouraged that no

seepage was noted around the roots

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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.

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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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What would you do?

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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

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Be prepared – constant diligence

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