DIS Design

Site Locations

Three experimental DISs have been installed within the dunes in Kure Beach, NC. Kure Beach is located in New Hanover County, south of Wilmington, NC. The project sites are located along Atlantic Avenue, near the sections with K, L, and M Avenues, as shown below. Click on the images for a larger view.

Figure: DIS Site Locations within Kure Beach, N.C.

Sites L and M

The Site L and M DISs were designed to capture all of the runoff from their associated watersheds during a 0.5 in/hr storm event. The design of each DIS was based on its watershed characteristics, shown below. Hydrologic analyses provided the number of chambers required to ensure that the total infiltration rate into the sand matched that of the peak stormwater runoff rate during a 0.5 in/hr rainfall event.

Table: Site L and M DIS and Contributing Watershed Information

Variable	Site L	Site M
Watershed Description	Mixed urban and residential	Mixed urban and residential
Watershed Area (ac)	4.7	8.0
Watershed CN	88	69
Watershed Rational C	0.80	0.70
Stormwater Beach Outfall Diameter(s) (in)	15	24
DIS Invert Elevation (ft)	9.35	11.40
Total Number of Chambers	12	22

Stormwater from each site was diverted, using a large concrete vault and weir, into a distribution pipe that split the flow into two sets of subsurface chambers (figure below, left). The vaults were also used to monitor the stormwater (Figure below, right).

Figure: Plan View of Site M DIS. Site L was installed similarly.	Figure: Interior View of Site M Diversion Vault. The Site L vault was similar.

The chambers, StormChambers^TM manufactured by HydroLogic Solutions, Inc., were installed approximately 2 ft below the surface and 6-8 ft above the mean water table. Their installation began with digging a trench, placing a 1 ft gravel layer on the floor of the trench, then a heavy nylon mesh, then the chambers. The chambers were then connected using screws and another layer of gravel was placed along the sides of the chamber banks. Next, a geotextile fabric was wrapped around the sides and top of the gravel and chambers. The excavated sand was then placed on top of the chambers and the dune surface was smoothed.

Figure: Generalized Profile View of the DIS.						Figure: Generalized End View of the DIS.

Lastly, dune revegetation took place during the growing season after installation (below, left). Native dune plants were planted throughout the impacted area and within one year, the density of the vegetation had returned to near the pre-construction state, shown below (right).

Figure: Dune vegetation planting (2006).						Figure: Dune vegetation re-establishment (2007).

Site K

The Site K DIS was also designed to capture the runoff from a 0.5 in/hr storm event. Overall, the design and construction of this system was similar to those at Sites L and M; however, a few modifications were made. First off, the watershed associated with Site K was a mostly urban and impervious watershed that was home to the business and tourist district. These factors produced higher stormflow, higher peak flowrates, and higher bacteria concentrations. In addition, this system was designed less conservatively to examine how the DIS would perform in a more challenging setting. The Site K DIS and watershed information is below.

Table: Site K DIS and Contributing Watershed Information

Variable	Site K
Watershed Description	Urban
Watershed Area (ac)	8.3
Watershed CN	N/A
Watershed Rational C	0.77
Stormwater Beach Outfall Diameter(s) (in)	24, 24, 15
DIS Invert Elevation (ft)	7.50
Total Number of Chambers	26

The first modification to the Site K DIS was the use of existing stormwater drop inlets, located within the street, as diversions, instead of the large concrete vaults at Sites L and M. Use of such a vault was not possible at Site K due to the dunes being lower in elevation and the considerable elevation drop associated with the vaults. In addition, the expense of purchasing and installing the vaults was much greater than modifying the existing drop inlets. As seen below (left), the existing drop inlets were modified with brick and mortar weirs walls and metal weir plates, the attachment of distribution pipes, and the installation of monitoring equipment. The existing connected stormwater beach outfalls were kept in place to act as overflows.

The second modification was the diversion of three storm pipes, instead of one, that were split into a total of four inputs (two per bank), instead of two inputs (one per bank), as seen in the figure below and to the right. This modification served several purposes: 1) Diversion of multiple outfalls into one system instead of several systems, 2) better utilization of the entire chamber banks, and 3)improved hydraulic performance. The third primary modification was placing the chamber banks lower in elevation, meaning closer to the water table. This modification was performed because 1) the dunes were lower in elevation and 2) examine impacts on hydraulic and treatment performance due to the decreased vertical separation of the system and water table

Figure: Top view of a Modified Stormwater Drop Inlet.	Figure: Plan view of the Site K DIS.

The StormChambers^TM were installed in a similar manner as those at Sites L and M. Profile and end views are shown below. However, the system was approximately only 5 ft above the mean water table. In addition, SedimenTraps^TM, manufactured by HydroLogic Solutions, Inc., were installed beneath the system at each distribution pipe input. These were used to capture sediment and trash in a confined, accessible area, instead of throughout the entire chamber floor.

Figure: Profile View of the Site K DIS.						Figure: End View of the Site K DIS.

Lastly, dune revegetation took place during the growing season after installation (below, left). Native dune plants were planted throughout the impacted area and within one year, the density of the vegetation had returned to near the pre-construction state, shown below (right).

Figure: Dune vegetation planting (2009).						Figure: Dune vegetation re-establishment (2010).