Morris Township Detention Basin

Many existing stormwater detention basins do not reach achievable results of non-point-source pollutant loading reduction. This is mainly due to the fact that the dry detention basin was initially designed for the sole purpose of flood-control. It is this correctable situation that has prompted watershed organizations, such as the citizen group the Great Swamp Watershed Association, as well as the local planning organization, the Ten Towns Great Swamp Watershed Management Committee, to call for the implementation of retrofitting measures to meet local water quality protection and improvement goals. The Great Swamp Watershed, an ecological region in Morris and Somerset County 55 square miles in size, contains a number of such basins.

The original demonstration project, started in 1996 by Nanping Zhang under the guidance of Dr. Q. Guo, was undertaken with the goal of providing solid data on the cost and effectiveness of retrofitting existing stormwater detention basins for water quality improvement. State regulators and regional planning boards need such data as an example to encourage similar retrofitting. In our previous studies by the water resources branch of Rutgers University’s Department of Civil and Environmental Engineering, it was determined that modification of the existing single-purpose basin in Morris Township, New Jersey off of Harter Road (Exit 33, Route 287) into an extended dry basin will achieve the most desirable non-point source (NPS) pollution (Want to know more about NPS? Click HERE) reduction results and is most acceptable to local communities. An extended dry basin detains a large portion of entered stormwater runoff to physically settle out particulate pollutants, and it retains a small portion of entered stormwater in a low marsh area to biologically remove dissolved pollutants. This greatly differs from the original design as it achieves longer detention times and greatly improves removal as the original 15 inch diameter outlet was modified to a 3 inch diameter outlet.

A floating riser, based on a similar water quality device used by the Ocean County Soil Conservation Service, has been added to improve the particulate settling efficiency at the outlet leading from the dry detention basin. The floating riser (pictured below) is an inexpensive, common sense approach to the improvement of the dry detention facility. As the dry detention portion of the extended dry basin relies nearly solely on settling for pollutant removal, it is desirable to remove the stormwater most near the surface at all times. A floating outlet connection will achieve this for the duration of the storm, in the end settling back to the basin floor to allow complete stormwater evacuation.

To distribute the stormwater between the proposed subsurface wetland or open marshland system and the dry detention system, a flow splitter has been designed. This innovative approach allows the first-flush of a typical design storm to enter the wetland area. The first-flush, theoretically the most pollutant laden, is then given the maximum possible treatment. The remainder of the storm is diverted for standard treatment in the dry detention facility. Both areas of the basin have been maximized for their given function: the first compartment for biological treatment and the second, physical removal.

We propose to implement our selected retrofitting technique in two linked flood-control basins in Morris Township. These basins have been in place for many years without maintenance or enhancement. Retrofitting these basins will reduce non-point source (What is NPS pollution? Click HERE!) pollutant loading to the Great Swamp National Wildlife Refuge and to the Passaic River and directly benefit the local ecological community. The Great Swamp watershed has become a major example of watershed protection on both the government and grassroots level and serves as an ideal location for retrofit application studies. The performance of the enhanced basins will be monitored rigorously with state-of-the-art, American Sigma automatic samplers, flow meters and rain gages and the monitored results will be presented in a manner that can be used to guide other basin retrofitting efforts.

As an equally important, additional objective of the project, we propose to develop two types of educational materials as well as take part in community outreach with local watershed government and citizen groups. The first collection of educational materials contains a general description of the retrofitting technique and will be targeted toward a wide spectrum of stakeholders as to inform them of the benefits and the relative simplicity of retrofitting existing systems for enhancement. The second includes in-depth technical materials that will be incorporated into our undergraduate and graduate curriculum and in our continuing education program at Rutgers University. This additional education component will accelerate the statewide NPS pollution reduction effort.

The first goal of the proposed continuation of the implementation project is to retrofit two connected dry flood control basins for non-point-source pollutant loading reduction. The achieved benefits from this cost-conscious set of modifications will serve as a model to the local watershed committee and to watershed groups across the state. This leads to the second and equally as important goal of providing a solid example for the statewide retrofitting effort and simultaneously generate technically sound educational materials.

The above six groups have been working effectively in the current demonstration project and will continue the joint efforts in the implementation phase of the project.

Data was, and will continue to be taken with two Sigma 950 Flow Meters used in conjunction with two Sigma 900 Portable Samplers. A flow meter and sampler is put at both the inlet and the outlet and both are triggered automatically. The inlet is equipped with a Sigma Rain Gauge which begins the sampling process and the outlet is activated by a preset flow level. The samplers both hold (24) 1000 ml polyethylene bottles which are filled in pairs at a preset interval for the duration of flow activity. One bottle in each pair is later "fixed" with acid (0.25 ml H2SO4) to preserve the samples. Once taken, the samples are immediately picked up by QC, Inc. in Pennsylvania.

The flow meters have the ability to record rainfall, sample times, flow, velocity, and water depth. All of these parameters are extremely valuable in the analysis of the water quality improvement. The flow-weighted mean concentration (FWMC) is based on this collected data and, as the name implies, bases the importance of each sample's characteristics on the volume of water represented by the sample (i.e. the volume of water to pass by the flow meter since the last sample).

This page was created on June 3rd, 1998 by Nicholas Agnoli, a graduate student within the Civil and Environmental Engineering Department at Rutgers, The State University of New Jersey. This page updated by Jud Wible on June 30, 2001.

All data and information on this page is the property of Rutgers, The State University of New Jersey.


Both the Sigma 900 Portable Sampler and the Sigma 950 Flow Meter used in conjunction at the outlet (picture taken before modification to 3 inch outlet and addition of floating riser) for the long term continuous monitoring of urban runoff quantity and quality