The
NJ Department of Protection recently proposed a new, statewide
nitrate dilution model in their revised rules for Water
Quality Management Planning.
It
will use a 2.0 mg/L nitrate standard to determine how closely septic
systems can be constructed. This was widely criticized because a
one-size-fits-all standard will not steer growth away from
environmentally sensitive land. For example, it is about ten times
the groundwater standard of 0.21 mg/L for forested areas in the
Preservation Area of the NJ Highlands.
Less
noted was that regional differences will be further obscured by
scale, because nitrate dilution will be modeled using large HUC11
stream basins instead of smaller HUC14s. Since they aggregate so many
individual watersheds, there are often distinct differences in the
geology of the upper and lower portions of major HUC11 basins.
Geology determines the natural chemistry of groundwater and surface
water, and its vulnerability to erosion and pollution. That will be
invisible to planners as long as the DEP encourages them to apply
one standard to such a large area.
Hydrologic
Unit Codes
A
true watershed is bounded by a ridgeline
that directs all surface drainage to a single point, usually where
the stream or river exits the watershed. The Continental
Divide is the principal ridgeline
of the Americas, dividing
watersheds
that drain into the Pacific Ocean from those that drain into the
Atlantic Ocean.
Hydrologic
Units Codes is a planning tool developed by the US Geological Survey
that nests watersheds. As the HUC
number gets larger, the drainage area gets smaller.
The
largest scale is the multi-state HUC2 regions. NJ is part of the Mid
Atlantic region,
that stretches from the Canadian border in NY and Vermont to southern
Virginia. Watersheds become nested within counties at the HUC8
scale. One HUC8 in NJ includes all the watersheds that drain into the
Atlantic Ocean in the counties of Monmouth, Ocean and Atlantic, from
Sandy Hook to the southern boundary of the Barnegat Bay watershed
(page
2, Figure 1).
HUC11s
are generally scaled to one or more watershed of rivers or large
streams, while HUC14s are scaled to single or grouped tributaries.
There are 150 HUC11s and 921 HUC14s in NJ (page
2 and Figures 2 and 3 on page 3).
The
Manasquan River Watershed: HUC11 vs HUC14
The
most accurate surface and groundwater model would be one that
acknowledges the diversity of the geology,
the soils
and rates
of recharge, and the topography (slide
4) within the watershed. It would be scaled to the level of
single or grouped tributaries rather than single or grouped
watersheds: HUC14, not HUC11 basins.
The
Manasquan River in Monmouth County is only one HUC11 watershed, but
it is ten HUC14 basins (shown in the map at the beginning of this
blog drawn with the DEP's online GEOWEB mapper). Here is what you miss when you use the wrong scale.
The
Manasquan River begins at the end of the Inner
Coastal Plain and ends in the beginning of the Outer
Coastal Plain. It starts out in green clay and ends up in beach
sand.
Its
headwater streams in Freehold and Howell downcut as they erode
through glauconitic
soils until the channels can no longer overflow their banks into
adjacent wetlands. Runoff stays trapped in the channel during storms
where it destabilizes
embankments.
Tributaries
flowing through the Kirkwood-Cohansey sands in the lower watershed in
Howell and Wall erode laterally. They are more stable than the
downcut headwaters because they can still overflow into wetlands.
Wetlands release excess stormwater back to the main channel
gradually, while downcut streams keep it in the channel.
There
are different stream morphologies: you will find more Rosgen
“F” streams in the upper watershed and more Rosgen “C”
streams in the lower watershed (page
TSE-3, Figure TS3E–1, and this 2002
Rosgen assessment). There are different freshwater habitats,
because the clay and silt fines of the Inner Coastal Plain blanket
the streambed and degrade macroinvertebrate
habitat more than the sandy soils of the Outer Coastal Plain
(slide
24).
You
can't build septic systems, or wish you hadn't, in the impermeable
Marlton
and Kresson clays in Freehold. Septics don't drain there, they
overflow. But downstream in Wall, the pebble-sands of the Kirkwood
Cohansey outcrop can be too porous for septic systems. When you
excavate a new drainage field you may need to mix the sand with
fine-grained fill to slow down the drainage so the septic system
doesn't pollute the groundwater.
Generally,
groundwater moves slowly and surface water moves quickly in the upper
watershed , then does the opposite in the lower watershed. The
Manasquan starts out as one river and ends up as another. But that is
moot when the rules only recognize the watershed as one continuous
HUC11.
Another
Override
There
was a lot more to dislike about these recent rule proposals by the NJ
Department of Protection: expanding
sewer capacity to 100% based on an unpublished study; weakening
protections in the Highlands; doing all this with a 20
year old Water Supply Master Plan. The Legislature should reject
the WQMP and
Capacity Assessment Plan rules.
Just
like the Senate, but not the Assembly has
done with an earlier DEP proposal that weakened core protections for
streams and rivers.
