Implementing Subsurface DrainageCorrectly implementing subsurface drainage in
an area serviced by open ditches requires more
than simply installing a minimum-sized culvert.
A proper analysis is necessary to determine
what effects introducing subsurface drainage
will have on the surrounding area, not simply
one parcel. The volume of water a ditch
conveys during and following rainfall must be
addressed. This requires consideration of the
characteristics of not only the proposed site
but upstream and downstream factors as well.
This information cannot be obtained by visiting
one residence and employing sound judgment.
It is possible and likely that areas miles away
will be affected.
Existing Driveway Culverts
Existing driveways throughout the parish
present a problem for the installation of
subsurface drainage. It is not uncommon for a
driveway culvert to be inadequately sized and
sloped. To correctly implement subsurface
drainage, installation must meet the elevation
of any existing culverts and provide for
appropriate flow. These requirements can be
contradictory when a system is constructed in
a piecemeal fashion.
Existing Subsurface Drainage
Subsurface drainage installed prior to 2008 has
created some problems. Many of the structures are
not graded properly, and some are partially or
completely filled with debris, substantially damaged
or continually hold water. Adding to a problematic
system without addressing the existing problems will
cause additional system failures.
Available Capacity
As Figure 1 demonstrates, installation of a pipe
into an existing ditch may reduce both capacity
and storage of the system. This further
demonstrates why a systematic approach to
drainage is necessary as opposed to
intermittent installation.
Legality
The parish has obtained legal guidance stating that
it may not expend funds on individual aesthetic
improvements to private property. This includes
the cost of hiring engineers or using parish
employees to size individual culverts to replace
existing drainage, as well as the actual installation
of said culverts.
Unless the parish is undertaking an improvement
that will result in the betterment of the parish,
such as improving the drainage for an entire
street or basin or rectifying a safety issue, such as
a roadway that is unsafe due to steep shoulder
slopes, the resident must undertake the cost to
both design and install the aesthetic improvement
in question.
“St. Charles Parish is prohibited from donating
public funds for the engineering of subsurface
drainage for the sole benefit of certain private
landowners. St. Charles Parish may, however, fund
these engineering costs if such an expenditure will
be in the best interest of the parish as a whole and
not just the private landowners who may receive
an indirect benefit of the engineering services.” – Attorney General of Louisiana, James Caldwell
Summary
The improper installation of subsurface
drainage can worsen parishwide systematic
drainage issues and reduce storage capacity.
The funds required to properly design and
install a subsurface drainage system makes it
a costly undertaking. Because a drainage
system needs to be designed as a whole, and
not just at a single residence, the design
needs to encompass an entire street, if not a
large area.
Additionally, the cost to maintain a closed
system is higher than the cost to maintain an
open ditch sytem. An open ditch can be redug
relatively quickly and cheaply, while a culvert
must be cleaned out with specialized
equipment.
Finally, the parish cannot legally expend funds
on subsurface drainage for aesthetic
purposes as described by the attorney general
of Louisiana, James D. Caldwell.