Reservoir Capacity: Another Reason for Low Impact Development

NJ American Water is sending a brochure with their bills: "More people. More sprinklers. More Demand. Same water supply." Same water supply?

NJAW offers a number of water-saving tips to avoid rate hikes for building a desalination plant or a new reservoir. The population in Monmouth County grew from 95,000 to 630,000 in the last hundred years, and the Swimming River Reservoir isn't big enough anymore - especially during the summer. It’s lacks capacity.

NJAW concludes: "Monmouth County has been blessed with steady growth, but is essentially using the same water supply that was in place decades ago." No it's not.

Flashy Streams = Less Holding Time in the Reservoir = Less Capacity

The water supply to the reservoir became smaller as woods changed into impervious surface – as the Swimming River Watershed was developed over the last several decades . (The SRR watershed is mapped here to the left of the words "Navesink River", and here on slide 8 to the left of the Navesink Estuary).

As fields are replaced by roads, roofs, and lawns, up to sixteen times more runoff drains into streams when it rains, according to Thomas Schueler of the Center for Watershed Protection. That means that only one-sixteenth of the rainfall is available to soak into the ground and become groundwater.

Because streams in the Swimming River watershed have become flashy, the reservoir fills up and empties faster than it did when the area was woods and fields. When rain is able to soak into the water table, it seeps into wetlands, then into streams, and then those streams flow into the reservoir, and out of it - over a longer period of time. That's crucial during a drought – increasing reservoir capacity by increasing holding time.

You can make graphs at this website of the rainfall from May 16-20 that was measured by a USGS gage at the Swimming River Reservoir. The second graph, titled "Gage height, feet", shows that it took about the same time for the reservoir to fill to “105% of capacity” as it did to lose it: half a day. It took only two more days for the reservoir levels to return to what they were before the storm.

In and out. Over the dam to the Navesink River and the ocean.

Low Impact Development, Ten Years Later

The 2004 Stormwater Regulations only required new, large construction projects in NJ to reduce runoff and redirect stormwater into the ground. The regulations were not fully implemented until 2007, according to Changes in Groundwater Recharge Resulting From Development in Atlantic, Mercer, and Sussex Counties, NJ, 1995 – 2007, by the NJDEP Geological and Water Survey.

Bill Wolfe, who recently spoke at the Brookdale Community College Environmental Club, has blogged about this report, which shows how successful the Stormwater Regulations could be for turning stormwater into groundwater. Runoff in these three counties from 2002-2007 (Table 8) could have been reduced by 35-88%, if New Jersey Stormwater Best Management Practices had been fully implemented.

That's for new construction. There is no mandate for all the homes and businesses built before 2007 to build a rain garden, or install pervious pavers in the driveway, or to use any other of the Low Impact Development practices. That would be expensive; many people do not have the money to do this, so LID is not likely to be mandated in the foreseeable future. It would be a hard sell - each individual would have to take responsibility for reducing the stormwater from their own property, just as everyone now has to collect and drag their recyclables to the curb.

Two Easy Ways to Reduce Runoff

NJAW suggests one LID technique, collecting rain from downspouts into a Rain Barrels and using it to water the lawn.

Another easy one is called downspout disconnection, according to the report "Barnegat Bay LID" by Princeton Hydro. Instead of letting the rain gutters drain down the driveway to the storm drain, you can reroute them so that they drain onto your lawn, at a reasonable distance from the foundation, where the rain will seep into the ground instead of becoming runoff. To work, the lawn has to have sandy soils that drain well and is graded so that rain flows away from the house.

These practices are not as effective as building a rain garden or installing pervious pavers, but collectively, the reduction in runoff would still be significant. In 2008, the Monmouth County Office of Geographic Information Systems predicted that one inch of rain produces about 3 million gallons of runoff just from the roofs on buildings east of Route 71 in Spring Lake, Spring Lake Heights, and Sea Girt.

The Front End: “Development Diminishes and ‘Takes’ Public Water Supplies”

That’s a quote from Bill Wolfe, who concludes that the NJDEP-GS report “makes the case for both stronger policies, in terms of stricter land use controls and storm water regulations, and some form of economic compensation (i.e. impact fees) by developers for the loss of groundwater recharge caused by development.”

He explains that the “loss of recharge is essentially ‘taking’ public property that should be paid for by the developer in terms of some form of impact fee, e.g. based on calculated loss of recharge or area of impervious surface and the value of [natural capital] consumed and permanently lost.”

He also recommends that “towns need to do build out capacity based land use planning and zoning that reflects the capacity of water resources. Towns like Hopewell (Mercer County) have done exactly this and provide a model.”

1+1=2

Wolfe concludes that none of this is going to happen soon. So here's what's left: “As our water supplies, ecosystems, and physical infrastructure become increasingly stressed and financial deficits magnify, all water users must begin to pay their fair share for “consumption”, whether at the back end use from the tap, or on the front end in terms of loss of recharge to source waters.”

So for now it’s still just the back end – NJAW customers may end up paying for new infrastructure to expand reservoir capacity due in large part to the loss of groundwater recharge.

Since dredging is not mentioned in the brochure, it's apparently not cost effective for expanding capacity. Why would NJAW want to pay for dredging when the reservoir is just going to silt in again because past land use practices are causing streams to erode?

That’s why any discussion of dredging needs to include LID. The NJDEP offers an easy way to begin.

Since LID can "reduce an existing [storm] water quantity issue", it can be included by a town or county as a nonbinding "Optional Measure" in their Stormwater Pollution Prevention Plan, as described in section NJAC 7:14A-25.6(i) of the 2004 Stormwater Regulations.

Voluntary LID, written into the municipal or county plan, for existing land use, nonbinding:

“Failure to implement an [Optional Measure] identified in the [Stormwater Pollution Prevention Plan] shall not be considered a violation of the NJPDES permit or this section.” It’s a start.

"Sunset" Period Changed to Seven Years in 2011

N.J.A.C. 7:14A, including Chapter 25, the Municipal Stormwater Regulation Program, looks like it was readopted on 1/5/2009. So if I am reading this correctly, it will come up for public comment in 2016. N.J.A.C. 7:8 (Stormwater Management) was last amended on April 19, 2010, so it should come up for public comment in 2017.

Worth following, because LID can reduce flooding too.