Billion Gallon Border: Part I - The Red Clay Creek Proposal

I'm excited and proud to present here another Guest Post from Robert Wilhelm. Bob has done some great research into the origins and construction of Hoopes Reservoir, and in this post and the next relates to us the story of how it came about. But first, this post tells the story of the reservoir that wasn't -- the proposed Red Clay Creek reservoir. I think you'll agree they ended up making the right call.

-- Researched and written by Robert E. Wilhelm, Jr

Hoopes Reservoir today

The centerline of the Red Clay Creek serves as the border between Mill Creek Hundred and
Christiana Hundred. During most days, the creek is only a few tens of feet wide. In the late 1920s, a proposal was seriously considered that would have changed the Red Clay Creek’s width to hundreds of feet for nearly a third of the creek’s length within Delaware. The City of Wilmington, needing another potable water reservoir to support a growing population and industry, studied flooding much of the Red Clay Creek Valley north of Wooddale for a reservoir that spanned both Mill Creek and Christiana Hundreds.

By the early 1900s, it was apparent to Wilmington Council members that any number of events might place the city’s reliance on the Brandywine Creek for potable water in jeopardy. While the city had reservoirs, they were proving inadequate. A study, commissioned in 1919, recommended an additional reservoir of at least a billion gallons be added to the city’s water systems for use during drought, Brandywine Creek contamination, or for emergency use.

In 1924, Wilmington commissioned a study as the first step for a project to eventually construct a large reservoir outside of city limits to store water for augmenting the Brandywine’s supply. Wilmington Water Department engineers considered multiple natural landscape locations associated with the Brandywine, White Clay, Christina, Pike, Red Clay, and Mill Creeks where land might be purchased for a new reservoir. Northern New Castle County’s Piedmont stream valleys are rich in spring-fed tributaries feeding creeks. This combination results in ideal natural opportunities for the creation of water storage lakes and reservoirs.

The Red Clay Creek Valley quickly became the prime contender for a new reservoir as it offered two potential sites close to Wilmington. Two ideal dam locations just north of Wooddale allowed for reservoirs along the Red Clay Creek or its tributary the Old Mill Stream. While industrial pollution from Yorklyn paper and fiber mills along with other infrastructure presented a concern for the Red Clay Creek Valley location, the fact that the Red Clay Creek is fed from numerous Pennsylvania springs and had the reputation as “that never-ending stream”, certainly made the Red Clay Creek Valley attractive for a reservoir. To provide the required minimum billion-gallons of storage capacity, the Old Mill Stream Valley, the eventual location chosen for the present Hoopes Dam and Reservoir, presented little infrastructure but required a massive dam to be constructed.

1927 B&O Valuation Image of Wooddale

1927 B&O Valuation Image of Spring Valley

Baltimore & Ohio Railroad photographs from 1927 show the potential dam site as well as an upstream flooded area of Mill Creek and Christiana Hundreds. With the guidance and assistance of Piedmont Geologist William ‘Sandy’ Schenck and Geologist Daniel Warner of the Delaware Geological Survey (DGS) at the University of Delaware, and access to DGS Light Detection and Ranging (LIDAR) two-foot topology data for northern Delaware, computer software now allows simulated flooding of the Red Clay Valley for a reservoir.

Wooddale & Spring Valley Topology with blue Hoopes Reservoir (top),
Detailed 2’ resolution LIDAR Topology Map of Wooddale (bottom)

Satellites and airplanes create LIDAR data for mapping the Earth’s surface in ultra-high accuracy three-dimensional form. The above upper image is DGS LIDAR terrain elevation data overlaying a Google terrain map. The LIDAR data gives a flat-looking Google terrain map of the Red Clay Valley north of Wooddale some 3D depth. The blue area is the present Hoopes Dam and Reservoir while the green areas are parks.

LIDAR data, when interpreted by computer, allows the generation of 3-dimensional topographic maps that include lines of equal elevation called a topo-lines. The topo-lines for a given elevation may be extracted and provide highly accurate length and area information among other useful data. The above lower image is a close-up of the Hoopes Reservoir and Dam region showing the LIDAR topographic lines at two-foot spacings used for this study.

The computer-generated image below is based on a Google terrain map of the subject area with digital overlays of roads, streams, and watersheds from FirstMap Delaware added for reference. Hoopes Reservoir is the prominent light blue area at the right in each image. Added to the map for 3-dimensional analysis is DGS LIDAR data providing a sense of the rolling piedmont landscape the Red Clay Creek flows across. The short red line (center bottom) between two large rock formations is where a proposed dam would have been located. The creek level at this point is 100-feet above sea level.

140-foot (top, lime green) and 150-foot (bottom, pale blue) Elevation Flood Contours

Using the 140-foot topo-line, we define an irregular shape (lime green in the above top image) which represents a water surface level of 140-feet above sea level (a dam with a spillway weir 40-feet above the dam’s base at creek level). From the dam at Wooddale, a reservoir would extend to the vicinity of the iron railroad bridge at Ashland next to the Creek Road (Route 82) road bridge. Based on LIDAR data, summing the calculations of volumes contained between elevation levels, the dam creates a reservoir pool of approximately 1.16 to 1.21 billion gallons of water. The results were verified against DGS calculations using 3^rd order mathematical equations for calculating estimated water volume. Creating a 40-foot deep pool of water behind a dam at Wooddale on the Red Clay provided the minimum reservoir the City of Wilmington required.

Adding five feet of height to the dam’s spillway weir would provide a deeper and larger storage pool of water and would flood some of the Ashland area where the Sharpless flour mills were operating at the time. Depending on the dam’s weir elevation, the mills might require relocation along with Ashland railroad station. Approximately 1.6 billion gallons of water might have been retained at full reservoir capacity.

The most likely proposed reservoir, flooding the valley to Sharpless Road, would have placed the spillway weir at 150-feet above sea level (pale blue area in above lower image) and provided roughly 2-billion-gallons for the City of Wilmington which would be equivalent to the present Hoopes Reservoir capacity when constructed (it was increased to 2.2-billion-gallons in 2008)

The proposed Red Clay reservoir required a dam just above Wooddale crossing both B&O tracks and Barley Mill Road (Route 82) between two high rocky bedrock features. A dam approximately 65-feet high physically, and spanning approximately 550-feet, with a spillway 50-feet above the creek-bed would have been needed. A reservoir pool stretching 2½ miles upstream to Sharpless Road and stretching to more than 2,500 feet wide in several locations would result. The Red Clay Valley storage pool would have a surface area of 315 acres (the present Hoopes Reservoir’s water surface area is 187 acres; both holding nominally 6,300 acre-feet of water). The Red Clay spillway would experience continuous flow from the Red Clay Creek as well as flow from Burrows Run and several other up-stream tributaries.

Unlike the present Hoopes Dam where little spillway water flows, a Red Clay dam spillway would always be active and even more impressive when frozen during winter months. A larger spillway in a Red Clay dam would have been designed to handle not only the 35,000 gallons per minute average flow of the Red Clay at Wooddale, but peak flows as high as 40,500 gallons per minute during most storms. In the 21^st century, the Red Clay at Wooddale has experienced flow rates at high as 140,000 gallons per minute. This flow rate would have probably overwhelmed a 1924 designed spillway causing the reservoir to pour over the top of the dam and endangering its structural stability.

The big detractors for the Red Clay Creek proposal were a $1-million price tag (nearly $14,750,000 today) the Baltimore & Ohio Railroad submitted as an estimated cost in 1928 to relocate their Landenberg Branch around the proposed reservoir. Additionally, relocating residents and closing down industry settled along the creek at Wooddale (Leach Quarry), Mt. Cuba (Speakman mills) and possibly Ashland (Sharpless mills) would be equally as expensive.

With a decision to relocate the infrastructure surrounding Ashland, the reservoir planners might have chosen to flood the valley an additional ten feet to the 160-foot elevation above sea level. This would have placed the flood pool in the vicinity of Garrett’s Lower Snuff Mill adjacent to Creek Road (Route 82). A 3.2-billion-gallon reservoir could have provided water storage for most of New Castle County well into the foreseeable future (image below, gray area represents the 160-foot elevation flood area) had this option been selected.

160-foot (top, gray) and 190-foot (bottom, dark blue) Elevation Flood Contours

The Red Clay Creek’s above sea level elevation as it crosses from PA into DE is 190-feet. Flooding of the Red Clay with a spillway at 190-foot above sea level elevation (dark blue in the lower image above) provides nearly 10-billion-gallons of water storage. The 190-foot elevation image provides additional useful information related to the general flow of the Red Clay Creek.

Downstream of Yorklyn where Garrett’s Lower Snuff Mill was located, as well as downstream of Ashland and the railroad’s iron truss bridge, the creek valley narrows significantly. When huge storms dump high volumes of rain within the Red Clay Watershed (watershed borders shown with red lines), the Red Clay tends to pool upstream of these natural restrictive locations. A severe downpour or multiple days of heavy rain saturating the ground causes the Red Clay Creek to rise and flood more land area due to the restrictions along its path at Yorklyn, Ashland, and where a dam was proposed at Wooddale. The sequence of images below step through the flood levels at ten-foot intervals starting with the creek’s level at the dam (100-foot elevation above sea level) to 190-feet above sea level. In the upper left corner is the elevation in feet above sea level.

In the next post, we'll look at the alternate location to the Red Clay reservoir, Old Mill Stream.