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environmental | Maydale Nature Center Water Quality Restoration
Maydale Nature Center Water Quality Restoration, Montgomery County, MD
The Maydale Nature Center Ponds are unique ponds which were not originally designed for the purposes of a stormwater management facility; however, the ponds do provide attenuation of discharges due to the riser structures and principal spillways. The ponds are in series with the upper pond being a fish stocked wet pond fed by a 4-inch diversion pipe from the Paint Branch Stream. This pond drains via a riser and principal spillway into the lower pond being a shallow retention with wetland fringes, which then discharges back into Paint Branch via a riser and principal spillway. The Paint Branch Stream is classified as a Use 3 stream. The approximate drainage area to the pond is 120 acres.
This project was unique since it is a visible/recreation nature facility visited by schools, nature lovers and the community, which used the Nature Center as a park. Due to trees along the lower 
pond existing embankment, and piping along the existing lower pond principal spillway the Maryland Department of the Environment-Dam Safety Division required that the trees be removed or the lower pond be breached. Due to strong community opposition of the trees being removed, the M-NCPPC decided to breach the lower pond.
The design consisted of the breach of the lower pond, removal of the riser and principal spillway, the provision of a natural spillway/spillway ditch conveyance system back to Paint Branch and the re-grading of the lower pond to provide a meandering wet pool, with plantable islands and benches. In order to lower the water temperature prior to entering Paint Branch the spillway ditch location was discussed with DNR and was designed through a lightly wooded section, in which the larger trees at the edges provided shading. In addition, a fish ladder comprised of drop log 
structures was designed to allow fish to migrate upstream in Paint Branch due to an existing four foot concrete weir wall, across the stream, that affected fish migration upstream.
Hydrology: Hydrologic modeling was performed for the stream, for the design of the fish ladder and determination of the 100-year floodplain and for the ponds to determine the existing release rates to mimic. From 1"=200' County topographic mapping, drainage areas were determined. RCN's, and Tc's were determined using SCS'sTR-55 Urban Hydrology for Small Watersheds. Discharges for the 1-, 2-, 10, 50- and 100-year storm events were determined using the TR-55 data and TR-20 Project Formulation-Hydrology model.
Fish Ladder Design: Discharges were developed using the same methodology as used for the ponds. Discharges were determined for the 1-, 2-, 5-, 50-, and 100-year storm events and the base flow determined by field measurements and the Mannings formula. A 100-year floodplain analysis was completed for the determination of the 100-year floodplain limits, various water surface elevations, velocities and shear stresses. This information was used to design/set the elevation of the log drop fish ladder structures. The log drop structures consisted of a notched log set across the stream with rock pools on either side. This enables the migration of the fish upstream. DNR reviewed and approved the analyses through the log drop structures.
Permits: Permits obtained included 404 Joint Permit (MDE, DNR, COE); Montgomery County Department of Permitting Services for Stormwater Management and Erosion/Sediment Control; M-NCP&PC for Natural Resource Inventory/Forest Stand Delineation (NRI/FSD); MDE Dam Safety approval and approval from DNR fisheries.
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