San Elijo Hills Storm DrainLine ‘N’

Watershed Diversion

AERIAL VIEWAERIAL VIEWFIRE STATION

Culvert Outlet

POND

San Elijo Hills Road

Elevation drop of 130 feet over distance of 370 feet.

VICINITY VIEW

Historic watershed

Line ‘N’ watershed

A car traveling Eastbound (in Westbound lanes) knocked over fire hydrant in front of Fire Station #4 on San Elijo Road.

Water flowed for 21 minutes starting at 4:40AM. 92,363 gallons of water spilled at a rate of 4398 gallons per minute. Figures provided by Vallecitos Water District.

There is evidence that not all the flow entered Drainage Line ‘N’. ‘Q’ refers to a volumetric flow rate at a given point – cubic feet per

second. Assuming all water did enter Drainage Line ‘N’ this incident would

be Q=9.8. Pre-development maximum flow entering Carr property is Q=4.0. For this short period of time, the water potentially entering Carr

property was 2½ times the pre-development maximum flow. This short term flow of Q=9.8 was less than 20% the anticipated

post-development flow of Q=53. Images of resulting damage follow……..

FIRE HYDRANT INCIDENTJune 18, 2009

Sediment Plume From Fire Hydrant Incident June 18, 2009

Looking West – Culvert outlet to the right, up slope. More intense mud as flow enters pond.

View of Sediment Plume from San Elijo Road

Riprap Accumulated Below Riprap Area

June 20, 2009 - After fire hydrant break January 31, 2010 – After some rains

After normal rains, missing rocks at bottom and accumulation of additional rocks above and to the left as well as erosion to the right of rocks.

BOULDER 1

Looking South – June 18, 2009 after fire hydrant break Looking South - June 20, 2009 after fire hydrant break

Looking South – Jan. 31, 2010 after some winter rains Looking North – June 20, 2009 after fire hydrant break

Erosion, apparently from fire hydrant incident, and progression of erosion around boulder from normal rain. Boulder is now in precarious top heavy location.

South Toward Property Line

South at fence line – June 18, 2009 South at fence line – January 31, 2010

June 18, 2009 after the fire hydrant break. In later photo, note erosion and rocks missing on the right and a buildup of transported on the left. 2X4 is for reference and is 45 inches long. No previous measurement was made but

distance from fence to ground appears to have increased.

North To Property Line Fence

January, 2008 June 20, 2009

Jan. 31, 2010 Survey stake in January, 2008 image indicates location of current fence. In January, 2008 area was well organized fragmented rock. After the fire hydrant break it eroded down to a mess of soil and rocks washed down from upstream. Most recent photo shows continued erosion from normal rainfall. Note transport of rock and soil as well as erosion on left and newly exposed tree roots. As of January 31, 2010, there was 31 ½ inches from fence wire to ground. This appears to be more than previous. This area appears to have reached another layer of somewhat well organized fragmented rock.

BOULDER 2January, 2008 June 20, 2009

January 31, 2010 Boulder 2 is approx. 50 feet South of property line.

Compared to January, 2008 there was a large buildup of rock and debris after the fire hydrant break. See additional scour of the vegetation mat and surface soil to the left.

Photo from January 31, 2010 shows effect of rainfall since June, 2009. Note the debris has been washed downstream along with additional erosion into what was the area of scour.

Continued downhill rock transport is obvious.

BOULDER 2 – April 14, 2010Sometime between January 31, 2010 and April 14, 2010 Boulder 2

toppled over. Now blocking previously eroded channel. Further erosion is inevitable.

LOWER BRUSH AREA

Looking North - June 20, 2009 after hydrant break Looking North – January 31, 2010

This area, about 150 feet South of property line, appears to have been deeply eroded by fire hydrant incident. Note still moist soil, jumbled rock and newly exposed roots.

More recent photo, after normal rainfall shows many rocks previously in the background and left have been washed downstream. The fractured rock in the lower left has been broken up and begun to be moved downstream, exposing a new level of fractured rock.

See new large boulder in center of later photo and further erosion in the upper / center and lower / right.

 

RIPRAP AREA BELOW CULVERT END STRUCTURE

Photo on left, January 31, 2010, shows 3+ foot eroded channel to West of riprap area just below culvert end structure during January rains.

On Friday, February 12, 2010 a truck from O’Connell Landscape Maintenance parked on the culvert access road and filled this channel with rocks. There were no additional rocks brought to fill in this area. The larger rocks used were slid over from the existing riprap area. This exposed areas of silt and soil which have built up within the existing riprap. The smaller rocks used for this filling job appear to have been gathered from the hillside nearby. This has exposed additional soil on the steep hillside to erosion in future storms. No filter fabric was used under this new riprap area.

This cosmetic fix extends the riprap area beyond the width of the City easement for drainage maintenance into the open space lot. This increased width, to approximately 24 feet, could not possibly be safely conveyed to the 2 foot wide pre-development channel at Carr property line.

Conclusion – June, 2010 Reports by Gary Piro and Soroosh Sorooshian address the damage that has already occurred and the potential for damage once further development takes place in the Line ‘N’ watershed.

Various reports supplied by San Elijo Hills state obvious, irrelevant information and avoid the main issues. These reports do acknowledge a 13 times increase in flow over Carr property due to drainage diversion.

Every rain brings further damage to the rip rap area, further erosion of the hillside, expansion of the historically very small watercourse channel and more sediment to the pond.