WASTE MANAGEMENT                                  PIH-95


                    Gravity Drain Gutter Systems

Daniel J. Meyer, The Pennsylvania State University

Phil Goodrich, University of Minnesota
Gerry and Lucille Luke, Conception Junction, Missouri
Jim Moore, Oregon State University

     A gravity drain gutter is a manure handling system which has
no  mechanical  parts and requires little or no dilution water to
remove manure from a building. The liquids and solids are held in
a gutter until sufficient depth of manure is available for drain-
ing manure out  through  removable  tightly  sealed  plugs.   The
drainage interval may vary from one day in narrow gutters for big
pigs to a month in wide and deep gutters.

     Manure can be removed from a swine barn by:  (1)  manual  or
mechanical  scraping,  (2)  flushing  with dump tanks, siphons or
pumping systems with automatic or manually controlled valves, (3)
continuous  flushing,  and  (4) gravity draining.  Flushing often
requires large amounts of water (over 50 gal./ft. of gutter width
per  day).  Flushing with recirculation from treatment lagoons is
not practical in all areas because  of  odor  nuisance  potential
from  associated  lagoons and/or soil types which don't seal ade-

     Gravity drain gutter systems can be  utilized  for  handling
liquid  manure  from  swine of all ages. Some gutter shapes are a
modification of the deep, narrow gutter developed  in  the  early
1960's  (Figure  1).  Modifications  to  the original 6-inch-wide
gutters include wider top widths, rounded bottoms, flatter slopes
to the bottom, and shorter lengths. A new option on gravity drain
gutters is a reversing hairpin gutter. This is an 18  in.  to  36
in.  deep  gutter  with  a  divider  wall and two plugs which are
alternately pulled. It has drastically changed swine manure  han-
dling systems.

     The ``Y'' and ``V'' gutter gravity drain systems have disad-
vantages  when compared to slotted floors over manure storages in
that they are more complicated to build,  and  result  in  higher
total manure system costs.

     Research has shown and field experience  has  verified  that
corrosive  gas production increases with storage time and storage
temperature.  To minimize gas production, a gravity drain  gutter
should  be  sized  to  fill  and  be emptied within four days. If
manure will remain in the gutter for more  than  one  week,  some
form  of  perforated  pit  pipe  ventilation should be considered
unless adequate airflow is available to dilute the concentration.
This would be the case with bigger pigs (i.e., 30 lb. plus).

Design of Gravity Drain Gutters

     Designing a gravity drain system involves its shape,  slope,
length, and outlet.

     Gutter shapes may vary considerably (Figure 1), with a trend
toward a flat bottom hairpin gutter. Some shapes have in common a
narrow section at the bottom of the gutter which receives all the
liquids  and  part  of  the  solids. A minimum accumulated manure
depth of 12 in. is adequate to allow the manure  to  flow  toward
the  outlet  when  the plug is pulled. The total depth of Y and V
gutters varies from 12 in. to 36 in. A common  feature  in  these
modified  gutters  is the bottom section which is narrowed to 6-8
in. This limits the number of days of storage  needed  to  attain
the minimum 12-in. draining depth.

     Another type of gutter which is quite different is the  rev-
ersing  hairpin gutter. Its depth can vary from 16 in. to 36 in.,
but the most common depth is 24 in.  The width can  vary  from  2
ft.  to  12  ft.  Farrowing  and nursery gutters should have per-
forated 6 in. to 8 in. diameter pit ventilation ducts  above  the
divider wall or a central plenum under the service alley which is
connected to high RPM (2800) exhaust fans to reduce pit gas  lev-
els  in  farrowing and nursery buildings (see PIH 60 ``Mechanical
Ventilation of Swine Buildings''). The primary advantage  of  the
hairpin over Y or V gutters is the reduced construction costs.

     Two types of side slopes to the Y and V gutter are used. The
first is a self-cleaning slope with a minimum of 1 in. rise per 1
in. run for farrowing and 1 in. rise per 3/4 in. run for nursery.
These  steep  slopes  work  well for nursery pens (4 ft.) housing
single litters. However, steep slopes require excavation that  is
too  deep for farrowing crates and long nursery pens with totally
slotted floors. The second type has flatter  slopes  to  decrease
construction  difficulty and cost. Slopes being used in this case
are up to 2 in. per foot for farrowing and up to 4 in.  per  foot
for  nurseries.  Because  flatter slopes accumulate manure solids
and feed, they should be hosed or scraped off every 1-2 weeks  to
reduce  ammonia  levels and fly populations. A combination of the
first and second type of  slope  can  be  used  beneath  elevated
totally  slotted  farrowing  crates  and  nursery pens. The self-
cleaning steep slopes are placed under the slotted floor sections
where  manure  concentrates  the heaviest. The flatter slopes are
placed under the remainder of the  pens.  Gutters  should  be  at
least  3-in. below slats so the manure can fall free of the slot-
ted floor.

     Gutter length of the Y and V gutters should  not  exceed  40
ft. for farrowing or nursery barns and 70 ft. for grower and fin-
isher barns. The exception is the hairpin gutter which can be  up
to  200  ft. long for growing-finishing buildings.  The preferred
building length is about 100 ft. If center plugs  are  used,  the
length  can  be doubled since the gutters drain from both ends to
the middle. The depth should be increased from  2  to  3  ft.  to
build  up  more flush force if longer gutters are used. A minimum
of one to two inches of water should cover the entire  bottom  of
the  gutter  before  using  it the first time. This initial water
also helps longer gutters to drain cleaner and  helps  hold  down
ammonia levels longer.

     The longitudinal slope of the gutter should be about  1  in.
of  drop  in 20-40 ft.  for Y or V gutters. The bottom of hairpin
gutters should not be sloped. If the  gutter  slope  is  steeper,
solids  remain on the upper end when the liquids flow out. Expect
a small deposit of solids on the upper end of the gutter.

     The preferred slat type over the Y and V gutters is one with
a high percentage open area, such as woven wire. The high percen-
tage open area allows for easy visual checking to  see  how  full
the  gutter  is,  and  how  much manure has built up on the slope
above the gutter. This type of slotted floor also  allows  easier
slope cleaning with a hose or a high-pressure washer.

     The outlet from the gutter must be equipped  with  an  easy-
to-remove  water  tight  plug. Three types are shown in Figure 2.
Fit the plugs into a 90-degree elbow or tee  (regular  or  saddle
type).  It  is better to have an overflow as part of the plug, in
case a waterer leaks or breaks, especially where hairpin  gutters
are  placed on top of concrete slats (i.e., in an existing build-
ing with concrete slats, a thin  concrete  cap  would  be  poured
before  adding  the gutters).  The ones shown have a built-in gas
trap to prevent backdrafting of pit gases when the barn has nega-
tive  pressure  ventilation.  Locate  the plug outside the pen or
crate to keep pigs from falling into the  gutter  unless  a  per-
manent  guard  is  used.  For  a multiple room facility, consider
locating the plugs in a common alley outside  the  rooms  (Figure
3).  However,  the  access to the drain must seal tightly to keep
air from entering the room over the gutter, and interfering  with
ventilation system performance. The main sewer line can be buried
outside the perimeter of the barn in case access  is  needed  for
maintenance. If the rooms are drained individually, a 6-in. diam-
eter main sewer pipe is adequate.  This depends somewhat on  room
size,  pit  or  gutter size. If the barn has 4 or more rooms, and
all gutter plugs will be pulled in a short interval, use an 8-in.
pipe.  A  perspective  view of the reversing hairpin gutters with
two plugs is shown in Figure 4. All plugs should be  at  least  8
in. in diameter.
Floor Cross Sections of  Gravity
Drain Gutters


     Nine cross-sections for farrowing crates are shown  in  Fig-
ures 5A through 5J.  Figures 5A, 5B, and 5J are examples that can
be used in remodeling  situations  to  build  above  an  existing
floor.  The other cross sections require new sites or the removal
of portions of existing floors. Only Figure 5F  shows  the  steep
slopes  which  are  self-cleaning;  the  others  require periodic

     The example in Figure  5A  utilizes  the  reversing  hairpin
gutter  under the entire crate. The divider wall must be anchored
to the gutter floor as shown with reinforcing to prevent  tipping
over. Gutter depth can vary from 16 in. to 24 in.  The alleys can
be raised higher than the gutter bottom to reduce  leakage  under
the  wall  into the alley or a keyway (1 in. x 1 in.) can be used
to tie the floor and wall together for a better seal.  The  walls
can  be 6" concrete block or 4" of poured concrete with reinforc-

     The example in Figure  5B  utilizes  a  formed  plastic  pan
(100-150  mm  thick) under the slotted floor. A 3-6 in. clearance
is needed between the flooring and the start of the  front  slope
for  access to wash down feed and manure solids.  Adequate clear-
ance is especially critical if the flooring has only a small per-
centage  of  slotted or open area. The alternative of washing the
slope directly through the slotted flooring may splash  too  much
water  on  the pigs unless they are moved out. The crates in Fig-
ures 5A, 5B, and 5J generally are raised at least 16 in.  if  the
existing  floor  is  to be left undisturbed. Crates elevated more
than 12 in. normally require a portable ramp for the sow  to  get
in and out.

     Figure 5C shows the bottom of the rear slope starting  about
18  in.  from  the  rear  of  the crate. Manure solids accumulate
mostly in the rear 24 in. of the crate. The  steeper  1-in.  rise
per 1 in. run slope helps in washing the solids into the gutter.

     The rear section of the gutter shown in Figure 5D is half of
a  large PVC pipe (generally 24-in. diameter) which collects most
of the manure solids. The minimum  slope  of  the  front  section
toward  the  half  pipe  is 1 in. per foot, but 2 in. per foot is
preferred. Some manure solids will accumulate on the slope to the

     The gutter shown in Figure 5E is similar to those in  Figure
5F  but  easier  to construct. Generally the bottom of the V is 6
in. wide and the top 2 to 2 1/2 ft. The depth is about 12  in.  A
disadvantage of the V-shape is that it takes about three times as
long as the Y-shape for the manure  level  to  reach  the  12-in.
depth needed for good drainage.

     Figure 5F shows two precast concrete gutters side  by  side.
The slope of the sides is about 1 in. rise per 1 in. run which is
needed for self-cleaning.  These 30-in. deep gutters have a  bot-
tom  section 6 in. wide and 12 in. deep plus they need to rest on
a flat slab as  sketched.  The  high  cost  disadvantage  of  the
gutters is somewhat offset by their accurate fabrication and by a
shorter installation time.

     Both cast-in-place gutters in  Figures  5G  and  5H  have  a
square  bottom  to  simplify  construction.  Figure 5H requires a
minimum of 1 in. per foot slope toward the gutter.

     In Figure 5J concrete blocks are used to elevate  the  crate
in  order  to  install a gutter. The deep gutter is a 6- or 8-in.
PVC pipe cut in half. A disadvantage of this gutter and Figure 5A
is  that  it takes much more time to fill to the needed depth for
good drainage than any of the other options.

     Gutters shown in Figures 5B and 5F can be purchased  commer-
cially whereas all the others must be cast in place.

Nursery Pen Gravity Gutter Design

     Five cross-sections for nursery pens are shown in Figure  6.
Figures  6A,  6B, and 6E adapt well for remodeling barns where it
is desirable to build above an existing floor. The  slope  toward
the  gutter should be a minimum of 1 in. per foot, but 3 to 4 in.
per foot is preferred. The gutter in  Figure  6A  is  constructed
using  two 8-in. blocks to form its bottom. It could also be con-
structed with a round instead of a  square  bottom  for  slightly
better  cleaning. The legs of the pen frame should be 3 in. above
the concrete block  stands  to  allow  access  for  cleaning  the
slopes.  The nipple waterers should be located over the gutter to
encourage pigs to drop manure there. The sides of the pen  toward
the  alleys  should  be  solid  up  to 16 in. high to keep manure
inside the pen. Prefabricated plastic is shown for the gutter and
the sloping area next to it. The plastic should be supported with
2 x 4's unless sand fill is used under the  plastic  for  support
(check manufacturer's recommendations).

     Figure 6C shows a narrow pen (4 ft.) with a Y-shaped  gutter
underneath. For self-cleaning, the slope should be 1 in. rise per
3/4 in. run. This would require a 3 1/2 ft. depth to  the  bottom
of  the gutter, assuming it has a 12-in.  deep bottom section. It
is critical that the pen flooring have ample open area  when  the
pen  is not elevated above the existing alley floor (for cleaning

     The gutter shown in Figure 6D can  be  cast  in  place  more
easily  than the Y- shaped gutter in Figure 6C.  A portion of the
area nearest the gutter is sloped more steeply  because  most  of
the  manure solids will fall through the floor at this end of the
pen (usually the end opposite the feeder). The 6-in. square  bot-
tom is also easier to construct than the rounded bottom Y- shaped
gutter in Figure 6C.

     The example shown in Figure 6E is similar to  the  farrowing
cross section in Figure 5A. The design and construction are simi-
lar. It is a simpler design than the other cross sections to con-
struct and cheaper to build.

Growing-Finishing Barn

     Figure 7 shows a sloped solid floor pen with 1 or 2  gutters
at  the  lower  end of the pen. Floor slopes, pen partitions, and
air flow patterns are critical considerations  for  keeping  pigs
resting  on the upper end and dunging near the lower end. Dunging
generally occurs in the open  partition  areas  where  the  floor
slope  is steep ( 1 in. per foot recommended). It is important to
have a 2-4 in. stepdown from the  resting  area  to  the  dunging
area. The dunging section should be a minimum of one-third of the
pen length. The depth of the gutter in Figures 7A and  7B  should
be  24  in. A pipe grating or guard over the gutter in Figures 7A
and 7B should be installed to protect small pigs. Square  gutters
work as well as semicircular gutters in finishing units.

     In Figure 7C, the floor between  the  gutters  has  a  steep
slope  (1  in.  per  foot)  for self-cleaning. This increases the
effective slotted floor area.

     Another option is shown in Figure 7D. The manure is held  in
2-ft.-deep  gutters, which are drained after the manure reaches a
12-in. depth. These gutters are the reversing hairpin type.  They
can work best in partially slatted pens. The maximum gutter width
is 12 ft. This requires a divider wall  unless  the  gutters  are
recharged  with  extra  water from a two stage lagoon. The recom-
mended maximum length is 100 ft. (200 ft.  of  draining  length).
High  moisture cracked corn feed can cause these gutters to drain
poorly. Wet feeders and gravity gutters do not work well together
due  to  the  reduced waterer spillage or dilution water. Grower-
finisher gutters fill faster than farrowing-nursery  gutters  and
can be drained more frequently so pit pipe or duct ventilation is
not as necessary.

     Reversing hairpin gutters  can  be  sealed  tighter  between
rooms  than  buildings  with  scraper systems. This is especially
important in naturally ventilated buildings.  A pressure  treated
hinged  door  works well below room divider walls to minimize air
exchange between rooms.

Manure Storage

     Manure can be stored in a concrete or glass-clad steel tank,
earthen structure, or an earthen treatment lagoon (the latter two
should  be  properly  sealed).   Note:  Storages  are  overloaded
lagoons  and  smell much worse in warm weather than cool weather.
At least 60 days of storage  time  (180  days  is  preferred)  is
recommended. Check state regulations for minimum storage criteria
and odor stipulations. Refer to PIH-67, ``Swine Waste  Management
Alternatives,''  for manure production per day and storage alter-

     Caution should be exercised when draining or pumping into  a
storage under another building or in the existing building if the
pit is capped since this will agitate  that  manure  and  release
gases. One of those gases is methane. If the drain plugs are left
out during cleaning and if the manure in  shallow  pits  above  a
deep  pit  is  drained out and if manure in the deep pit is being
emptied, the possibility of fire exists from  methane  gas  since
most  heaters are unvented or have open flames. A negative venti-
lation system is essential in the pit to reduce  gasses  released
into  the  building  or room connected to the storage via a drain
plug or drain pipe.

Manure Transfer Systems

     If possible, design the system so that manure flows  to  the
storage  by  gravity.  The drain pipes for the plugs should be at
least 6 in. for farrowing and nursery buildings to prevent  plug-
ging,  with  the  exception  being  the reversing hairpin gutters
which should have a minimum  8  in.  diameter  pipes.  Eight-inch
drain    pipes    are   suggested   for   finishing   barns   and
gestation/breeding buildings.  Slope the 6-inch and  8-inch  pipe
at  least  1%  (1/8  in./ft.) to 2% (1/4 in./ft.) to achieve good
cleaning velocities. The maximum distance  between  cleanouts  in
the drain pipe should not exceed 300 ft. The storage inlet should
be at least 3 ft. above the bottom since solids  tend  to  settle
out at the point where the manure enters the storage.

     To obtain sufficient slope for gravity transfer  of  manure,
it  may  be  necessary to construct the barn floor on extra fill;
otherwise, storage capacity is lost  by  not  using  all  of  the
available height. Another alternative is a collection sump with a
pump to lift the manure into the storage (for  sump  information,
see  PIH-91, ``Pumping Liquid Manure from Swine Lagoons and Hold-
ing Ponds''). Use a pump large enough to handle 1 1/2 in.  diame-
ter solids.

Gutter Construction

     The gutters can be (1) assembled from commercially available
prefabricated  plastic, fiberglass, or precast concrete sections;
(2) cast-in-place concrete or (3) a  combination.  The  Y  and  V
gutters  are  more costly to construct than the reversing hairpin
gutters because of the steeper slope involved.

Prefabricated and Precast

     The plastic gutter sections are joined together with a seal-
ing  tape  or  caulking compound and bolts or channel brackets at
the joints. Installation of below-floor plastic gutters  requires
inner bracing to prevent the sand backfill or fresh concrete from
pushing in the form, and weights or temporary bracing to keep the
gutter in place.

     Precast concrete gutters also are used in below-floor appli-
cations.  Minimal  excavation is needed with the precast concrete
sections. They are set on a sloped footing and are stable without
bracing  or  anchoring.  The  sections  are  mortared together to
prevent leaks.


     Commercial steel forms, which are available  for  Y-gutters,
can  be set in excavated trenches and anchored to the surrounding
concrete floor with lag bolts or weighted with sandbags. Concrete
for  the  alleys  is placed before the trench is excavated with a
small backhoe. Commercial plywood forms can also be set in  exca-
vated  trenches.  They are temporarily braced to the roof trusses
to prevent uplift. When gutter forms are used,  the  concrete  is
generally  poured  in  one  step  and  should be well vibrated to
ensure a smooth finish without voids.

     Generally, the bottom of cast-in-place concrete  gutters  is
constructed  first,  using the excavated soil as the outside form
(Figure 8). An inner frame with short spacer blocks will form the
inner  wall.  The wood grain should run vertically so that blocks
can be split and removed. Fresh concrete should  be  vibrated  to
fill  the space beneath the inner frame, to prevent water leakage
from the gutter, and to provide a smooth surface. A  semicircular
bottom  can  be  constructed by cutting a 6- or 8-in. PVC pipe in
half lengthwise and nailing the half-pipe in the  bottom  of  the
inner frame.

     Two methods have been used to form the steep slope in the V-
or  Y-shaped gutters (3 in. to 12 in. per foot). The first method
utilizes reinforcing bars (3/8 in.) placed vertically every 4 ft.
in  the gutter and extended up the sideslope.  The soil forms the
sideslope for the underside of the concrete form. If the concrete
is  very  stiff  and  reinforcing  mesh is placed over the rebars
(above the soil), then the concrete sideslope can be troweled  in
place. This is a time-consuming method, but it requires no forms.

     The second method for the steep slope construction is to use
existing  soil  or fill for the underside form. Stakes are driven
as shown in Figure 8. A piece of wood is nailed to the top of the
stakes  to  form  a slat ledge ( make it the same as the depth of
the slats). Then, plywood is nailed to this piece  of  wood.  The
plywood  is  braced  to  the  roof trusses or weighted to prevent
uplift.  After the concrete has set 1-2  hours,  the  plywood  is
taken  off and the concrete steel troweled. Another way to give a
quick, smooth finish with little troweling is to line the plywood
with 4-6 mil polyethylene plastic or its equivalent.


     When remodeling requires new concrete  on  top  of  existing
concrete,  the  minimum thickness of the new concrete should be 2
1/2 in. if reinforcing wire mesh is used or  3  1/2  in.  without
reinforcement.  Use  seven bags of cement per cubic yard, and pea
gravel (1 in. maximum) for the thinner concrete.

Foundation Insulation

     When gutters are placed next to an outside wall  foundation,
insulation  is needed to minimize freezing in the gutters in cold
climate areas. At least 2 in. of a water-resistant  foam  insula-
tion  along  side  the  foundation  or  in the foundation wall is
recommended (see PIH-65 on ``Insulation for Swine Housing'').

Management of the Gravity Gutter


     A biological slime must form on the Y and V gutter sides and
bottom  to  get good cleaning action when the gutter contents are
emptied. This will naturally occur in 3-4 weeks. If solids remain
in  the  upper end of the gutter during this initial period, they
should be removed manually or hosed down.

Draining Gutter

     It is important to have the gutter filled to at least  an  8
in.  to  12  in.  depth  before emptying the contents in order to
scour solids from the upper end. When replacing the plug or gate,
wiggle  it  in  the slot or seat to be sure the outlet is tightly
closed. The Y and V gutters should be drained at least every week
to  ensure lower barn odor levels and good bottom scouring action
in the gutter.  The hairpin gutters  which  are  drained  at  2-4
weeks  will  have more odor than Y and V gutters unless pit ducts
are used above or on the side of the gutters.  With adequate air-
flow  in  larger  pig buildings (grower and finisher) the odor is
very minimal especially with partial slat  building  where  insu-
lated  sidewall ventilation doors or insulated curtains are used.
The reversing action of  pulling  alternate  plugs  keeps  solids
buildup  minimal.  If  the producer wants to completely clean the
gutter of manure, he will need to be able to add water on the end
opposite the plugs.  There should not be a lip at the plug.

Water in Gutter

     Adding one inch or more of water to the gutter after  drain-
ing will facilitate better drainage of the gutter next time, par-
ticularly if it is greater than 40 ft.  long.  A  nipple  waterer
over  each  gutter  ensures  having  extra  dilution water in the
gutter. This is especially critical in reversing hairpin gutters.
This  can  be  done  by  staggering  the waterers in the dividers
between pens.  ``Wet'' feeders where nipple waterers are over the
feed  trough  minimize  waterer spillage. Wet feeders and gravity
manure systems do not mix! The manure will be too thick  to  flow
unless extra water is always added initially.

|                                                                  |
|                                                                  |
|Safety                                                            |
|                                                                  |
|     Do not enter collection sumps, manure storages,  or  hauling |
|tanks, unless they have been and are being well-ventilated. Also, |
|do not enter these structures without a self-contained  breathing |
|apparatus  or  an  air  line.  In addition, a body harness with a |
|lifeline should be used, with two  people  standing  by  who  are |
|capable of lifting a person from the storage.                     |

Meyer, D. J. and J. C. Converse. Gas Production vs. Storage  Time
on Swine Nursery Manure. ASAE Paper 81-4512.

Avery, G. L., G. E. Merva, J. B. Gerrish. Hydrogen  Sulfide  Pro-
duction in Swine Confinement Units. Trans. ASAE 1975. p. 149-151.

Figure 1. Typical gravity drain gutters.

Figure 2. Alternative watertight plugs for gutter outlets.

Figure 3. Detail of main sewer line connection to gutter plugs.

Figure 4. Perspective view of reversing hairpin gutter.

Figure 5. Alternative farrowing crate floor cross-sections  using
gravity drain gutters.

Figure 6. Alternative  nursery  pen  floor  cross-sections  using
gravity drain gutters.

Figure 7. Alternative finishing  pen  floor  cross-section  using
gravity drain gutters.

Figure 8. Cross-section 0f a Y-gutter form for cast-in-place (two
stage process)

NEW 12/90 (5M)

Cooperative Extension Work in  Agriculture  and  Home  Economics,
State  of Indiana, Purdue University and U.S. Department of Agri-
culture Cooperating. H.A. Wadsworth,  Director,  West  Lafayette,
IN. Issued in furtherance of the Acts of May 8 and June 30, 1914.
It is the policy of the Cooperative Extension Service  of  Purdue
University  that  all  persons  shall  have equal opportunity and
             access to our programs and facilities.