Historic Dams and Local Streams, Lancaster County, PA By Matthew W. Kofroth Lancaster County Conservation District What Do Most Lancaster County Streams Look Like Today? Furnace Run Hammer Creek Little Chiques Creek Mill Creek Where Does All That Sediment Go? Sediment Plume from Hurricane Ivan 9/21/04 Lancaster County Susquehanna River Sediment Plume Chesapeake Bay ~60,000 Mills in 1840 US Census in Eastern US Lancaster County Chesapeake Bay Watershed Mill Density, #/km2 0.0-0.015 Piedmont 0.015-0.03 Physiographic 0.03-0.06 Province 0.06-0.09 0.09-0.12 0.12-0.15 0.15-0.18 0.18-30.00 0 500 Km PA COUNTY #MILLS, 1840 MILL DENSITY/SQ MI Montour 75 0.57 Sullivan 250 0.55 Wyoming 210 0.52 Montgomery 247 0.51 Fulton 225 0.51 Carbon 185 0.48 Northampton 179 0.46 Union 139 0.43 Chester 323 0.42 Philadelphia 60 0.41 Lancaster 383 0.40 Lehigh 126 0.37 Bridgen’s 1864 Atlas Mascot Mill Dam On Mill Creek Lititz Run Mill Creek Mill Creek Mill Dam Bridgen’s 1864 Map Impact of Water-Powered Mills on Sediment Storage Impact of Water-Powered Mills on Sediment Storage Impact of Water-Powered Mills on Sediment Storage Impact of Water-Powered Mills on Sediment Storage Impact of Water-Powered Mills on Sediment Storage dam Longitudinal Stream Profiles with Mill Dams and Mill Ponds, Lancaster Piedmont, PA Mill Creek W. Br. L. 170 Little Conestoga Conestoga and Swarr Run 130 Levan’s Mill Denlinger’s Mill 90 Conestoga River Elevation, meters VE ~ 333 x 50 Distance Downstream, km Average Dam Height 2.4 m Actual Dam Height (actual height unknown) Levan’s and Stoneroad Mills, Little Conestoga Creek, 1938 Air Photo Stoneroads Dam & Levan’s Dam & USGS Gage Levan’s Mill Dam Little Conestoga Creek Dam built in 1856, 8 ft (2.4 m) high dam- induced riffle 1.5 m 3 m legacy 0.5 m sediment eroding upstream of breached dam Legacy Sediments near Levan’s Mill Dam, L. Conestoga Creek Buried Colonial road Buried and saw mill Pre-Colonial Waterway (9,000 to 300 BP) Buried tree stump Denlinger’s Mill, W. Br. Little Conestoga Creek 0~2 km Denlinger’s Mill Bridgen’s 1864 Atlas of Lancaster County, Manor Township Mill Pond Reservoir Sediment Stack 5 m thick Denlinger’s Mill—Remnants of 18th century dam downstream Top of Bank Silty Clay 5 m (pond sediment) (20 ft) Leaf Mat Peat 1660-1810 AD 1510-1660 AD Creek Denlinger’s Mill, W. Br. Little Conestoga Cr. Core Sites & Mill Dam (20 ft high) ca. 1736 Legacy Sediment Buried Dam Big Spring Run Mill Dam Gypsy Hill Road, Near Mouth at Mill Creek Big Spring Run, West Lampeter Twp Meandering path of Big Spring Run developed after dam breaching downstream. Big Spring Run Big Spring Run Buried pre-settlement valley bottom SWARR RUN, LITTLE CONESTOGA WATERSHED (under stream restoration) Trench Perpendicular to Stream Peat 380 ± 60 yrs BP Basal angular gravel layer >1000 to 9000 yrs BP Implications for Stream Restoration Reach 3 Post-settlement Conditions Reach 2 Reach 1 Restored (~pre-settlement) Conditions Flood Flow Root Zone 2 - 10’ Legacy Sediments Flood Flow Historic Floodplain Historic Floodplain Base Flow Base Flow Gravel Gravel Bedrock Bedrock Chester County Stream Pumping Station Dam on Hammer Creek How Do You Fix It? Leave it Alone Approach Engineered or Hard-Armor Approach Work With What You Have in a Natural Approach Plant the Heck Out of it Approach Historic Natural Approach (lots of engineering required) Thank You Questions? .