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Military

Chapter 5

Route Classification

This chapter describes how to perform the technical aspects of a route recon. Route classification is a tool that helps determine what can travel down a road network and how fast it may travel. Routes are reconned, and the results are displayed on map overlays. During war or military operations other than war (MOOTW), only the necessary and essential facts about a route are gathered as quickly and safely as possible. (This information is placed on a route-classification overlay and supplemented by additional reports.) During peacetime operations, detailed route-classification missions are performed to obtain in-depth information for future use.
Route classification may be conducted in a high-threat environment. The same tenets that guide tactical recons apply to technical recons. All recons must be coordinated with the supported unit. Combined-arms support should be planned and rehearsed to support the recon.
The first step in understanding the technical portions of a route recon is understanding what information is needed to complete a route-classification overlay.

ROUTE-CLASSIFICATION OVERLAY

A route-classification overlay graphically depicts a route's entire network of roads, bridge sites, and so forth. (These items are reconned, and the data recorded as support documentation for the complete route.) A route classification gives specific details on what obstructions will slow down a convoy or maneuver force along a route. Engineers are the experts on route classification.

As a minimum, the following information will be included on the route-classification overlay (see Figure 5-1):

  • The route-classification formula.
  • The name, rank, and social security number (SSN) of the person in charge of performing the classification.
  • The unit conducting the classification.
  • The date-time group (DTG) that the classification was conducted.
  • The map name, edition, and scale.
  • Any remarks necessary to ensure complete understanding of the information on the overlay.

Figure 5-1. Route-classification overlay

ROUTE-CLASSIFICATION FORMULA

A route classification must include every alternate road on which movement can be made and what type of vehicle and traffic load that specific portion of the route can handle. Routes are classified by obtaining all pertinent information concerning trafficability and applying it to the route-classification formula. DA Forms 1248, 1249, 1250, 1251, and 1252 are designed to help organize recon data. These forms are covered in greater detail later in this chapter. The route-classification formula is derived from the information gathered during the route recon. The formula is recorded on the route-classification overlay (see Figure 5-1) and consists of the following:

(1) Route width, in meters.

(2) Route type (based on ability to withstand weather).

(3) Lowest military load classification (MLC).

(4) Lowest overhead clearance, in meters.

(5) Obstructions to traffic flow (OB), if applicable.

(6) Special conditions, such as snow blockage (T) or flooding (W).

Example:5.5/Y/30/4.6(OB)(T or W)
 (1)(2)(3)(4)(5)(6)

Route Width

The route width is the narrowest width of traveled way on a route (see Figure 5-2). This narrow width may be the width of a bridge, a tunnel, a road, an underpass, or other constriction that limits the traveled-way width. The number of lanes is determined by the traveled-way width. The lane width normally required for wheeled vehicles is 3.5 meters; for tracked vehicles it is 4.0 meters.

Figure 5-2. Route Widths

According to the number of lanes, a road or route can be classified as follows:

  • Limited access--Permits passage of isolated vehicles of appropriate width in one direction only.
  • Single lane--Permits use in only one direction at any one time. Passing or movement in the opposite direction is impossible.
  • Single flow--Permits the passage of a column of vehicles and allows isolated vehicles to pass or travel in the opposite direction at predetermined points. It is preferable that such a route be at least 1.5 lanes wide.
  • Double flow--Permits two columns of vehicles to proceed simultaneously. Such a route must be at least two lanes wide.

Route Type

The route type is determined by its ability to withstand weather. It is determined by the worst section of road on the entire route and is categorized as follows:

  • Type X--An all-weather route that, with reasonable maintenance, is passable throughout the year to a volume of traffic never appreciably less than its maximum capacity. This type of route is normally formed of roads having waterproof surfaces and being only slightly affected by rain, frost, thaw, or heat. This type of route is never closed because of weather effects other than snow or flood blockage.
  • Type Y--A limited, all-weather route that, with reasonable maintenance, is passable throughout the year but at times having a volume of traffic considerably less than maximum capacity. This type of route is normally formed of roads that do not have waterproof surfaces and are considerably affected by rain, frost, thaw, or heat. This type of route is closed for short periods (up to one day at a time) by adverse weather conditions during which heavy use of the road would probably lead to complete collapse.
  • Type Z--A fair-weather route passable only in fair weather. This type of route is so seriously affected by adverse weather conditions that it may remain closed for long periods. Improvement of such a route can only be achieved by construction or realignment.

Military Load Classification

A route's MLC is a class number representing the safe load-carrying capacity and indicating the maximum vehicle class that can be accepted under normal conditions. Usually, the lowest bridge MLC (regardless of the vehicle type or conditions of traffic flow) determines the route's MLC. If there is not a bridge on the route, the worst section of road will determine the route's overall classification.

In cases where vehicles have a higher MLC than the route, an alternate route may be sought or an additional recon of the roads within the route may be necessary to determine whether a change in traffic flow (such as single-flow crossing of a weak point) will permit heavier vehicles on the route. When possible, ensure that the route network includes a number of heavy-traffic roads, as well as average-traffic roads. This helps staff planners manage heavy-traffic loads to decrease the bottleneck effect.

The entire network's class is determined by the minimum load classification of a road or a bridge within the network. These are the broad categories:

  • Class 50--average-traffic route.
  • Class 80--heavy-traffic route.
  • Class 120--very heavy-traffic route.

Overhead Clearance

The lowest overhead clearance is the vertical distance between the road surface and any overhead obstacle (power lines, overpasses, tunnels, and so forth) that denies the use of the road to some vehicles. Use the infinity symbol () for unlimited clearance in the route-classification formula. (Points along the route where the minimum overhead clearance is less than 4.3 meters are considered to be an obstruction.)

Route Obstructions

Route obstructions restrict the type, amount, or speed of traffic flow. They are indicated in the route-classification formula by the abbreviation "OB." If an obstruction is encountered, its exact nature must be depicted on the route-classification overlay. Obstructions include--

  • Overhead obstructions such as tunnels, underpasses, overhead wires, and overhanging buildings with a clearance of less than 4.3 meters.
  • Reductions in traveled-way widths that are below the standard minimums prescribed for the type of traffic flow (see Table 5-1). This includes reductions caused by bridges, tunnels, craters, lanes through mined areas, projecting buildings, or rubble.
  • Slopes (gradients) of 7 percent or greater.
  • Curves with a radius of 25 meters and less. Curves with a radius of 25.1 to 45 meters are not considered to be an obstruction; however, they must be recorded on the route-recon overlay.
  • Ferries.
  • Fords.

Table 5-1. Traffic-flow capability based on route width

 

Limited
Access

Single
Lane

Single
Flow

Double
Flow

Wheeled At least 3.5 m 3.5 to 5.5 m 5.5 to 7.3 m Over 7.3 m
Tracked and combination vehicles At least 4.0 m 4.0 to 6.0 m 6.0 to 8.0 m Over 8 m

Snow Blockage and Flooding

In cases where snow blockage is serious and is blocking traffic on a regular and recurrent basis, the symbol following the route-classification formula is "T." In cases where flooding is serious and is blocking traffic on a regular and recurrent basis, the symbol following the route-classification formula is "W."

EXAMPLES OF THE ROUTE-CLASSIFICATION FORMULA

The following are examples depicting the use of the route-classification formula:

  • 6.1m/Z/40/--A fair-weather route (Z) with a minimum traveled way of 6.1 meters, and an MLC of 40. Overhead clearance is unlimited () and there are no obstructions to traffic flow. This route, based on its minimum traveled-way width, accommodates both wheeled and tracked, single-flow traffic without obstruction.
  • 6.1m/Z/40/(OB)--A fair-weather route (Z) similar to the previous example, except there is an obstruction. This obstruction could consist of overhead clearances of less than 4.3 meters, grades of 7 percent or greater, curves with a radius of 25 meters and less, or fords and ferries. A traveled way of 6.1 meters limits this route to one-way traffic without a width obstruction. If the route is used for double-flow traffic, then 6.1 meters of traveled way is considered an obstruction and is indicated in the formula as an obstruction.
  • 7m/Y/50/4.6(OB)--A limited, all-weather route (Y) with a minimum traveled way of 7 meters, an MLC of 50, an overhead clearance of 4.6 meters, and an obstruction. This route width is not suitable for double-flow traffic (wheeled or tracked). This width constriction is indicated as OB in the route-classification formula if the route is used for double-flow traffic.
  • 10.5m/X/120/(OB)(W)--An all-weather route (X) with a minimum traveled-way width of 10.5 meters, which is suitable for two-way traffic of both wheeled and tracked vehicles; an MLC of 120; unlimited overhead clearance; an obstruction; and regular, recurrent flooding.

CURVE CALCULATIONS

The speed at which vehicles move along a route is affected by sharp curves. Curves with a radius of 25 meters and less are obstructions to traffic and are indicated by the abbreviation "OB" in the route-classification formula and identified on DA Form 1248. Curves with a radius between 25.1 and 45 meters are recorded on the overlay but are not considered obstructions.

MEASURING METHODS

There are several ways to measure curves: the tape-measure, triangulation, and formula methods.

Tape-Measure Method

A quick way to estimate the radius of a sharp curve is by using a tape measure to find the radius (see Figure 5-3). Imagine the outer edge of the curve as the outer edge of a circle. Find (estimate) the center of this imaginary circle; then measure the radius using a tape measure. Start from the center of the circle and measure to the outside edge of the curve. The length of the tape measure from the center of the imaginary circle to its outer edge is the curve's radius. This method is practical for curves located on relatively flat ground and having a radius up to 15 meters.

Figure 5-3. Tape-measure method

Triangulation Method

You can determine a curve's approximate radius by "laying out" right triangles (3:4:5 proportion) at the point of curvature (PC) and point of tangency (PT) locations (see Figure 5-4). The intersection (o), which is formed by extending the legs of each triangle, represents the center of the circle. The distance (R) from point o to either point PC or PT represents the curve's radius.

Figure 5-4. Triangulation method

Formula Method

Another method of determining the curve's radius (see Figure 5-5) is based on the formula (all measurements are in meters)--

R = (C2/8M) + (M/2)

where--

R = radius of curve

C = distance from the centerline of the road to the centerline of the road at the outer extremities of the curve

M = perpendicular distance from the center of the tape to the centerline of the road

NOTE: When conditions warrant, set M at 2 meters from the centerline, then measure C 2 meters from the centerline. Use this method when there is a time limitation or because natural or man-made restrictions prevent proper measurements.

Figure 5-5. Formula method

Example: If C is 15 meters and M is fixed at 2 meters, the formula becomes--

R = (152/16) + 2/2

The result of this calculation would be an obstruction to traffic flow, and "OB" would be placed in the route-classification formula.

CURVE SYMBOL

Sharp curves with a radius of 45 meters or less are symbolically represented on maps or overlays by a triangle that points to the curve's exact map location. In addition, the measured value (in meters) for the radius of curvature is written outside the triangle (see Figure 5-6). All curves with a radius of 45 meters are reportable and need to be noted on DA Form 1248.

Figure 5-6. Curve symbols

SERIES OF SHARP CURVES

A series of sharp curves is represented by two triangles, one drawn inside the other. The outer triangle points to the location of the first curve. The number of curves and the radius of curvature for the sharpest curve of the series are written to the outside of the triangle (see Figure 5-6).

SLOPE ESTIMATION

The rise and fall of the ground is known as the slope or gradient (grade). Slopes of 7 percent or greater affect the movement speed along a route and are considered an obstruction. The percent of slope is used to describe the effect that inclines have on movement rates. It is the ratio of the change in elevation (the vertical distance to the horizontal ground distance) multiplied by 100 (see Figure 5-7). It is important to express the vertical distance and the horizontal in the same unit of measure. Report all slopes greater then 5 percent on the route-classification overlay.

Figure 5-7. Percent-of-slope formula

PERCENT OF SLOPE

The following methods are used for determining the percent of slope:

Clinometer Method

A clinometer is an instrument that directly measures percent of slope. It can be found in engineer survey units, as part of an artillery compass, and as part of an engineer platoon sketch set. Follow the instructions included with the instrument.

Map Method

Use a large-scale map (such as 1:50,000) to estimate the percent of slope quickly. After identifying the slope on the map, find the difference in elevations between the top and bottom of the slope by reading the elevation contours or spot elevation. Then, measure and convert the horizontal distance (usually road distance) to the same unit of measurement as the elevation difference. Substitute the vertical and horizontal distances in the percent-of-slope formula and compute the percent of slope (see Figure 5-8).

Figure 5-8. Map method to determine percent of slope

Pace Method

The pace method is a quick way to estimate percent of slope. Determine, accurately, the height and pace of each soldier for each member of a recon team before using this method. As a rule of thumb, the eye level of the average soldier is 1.75 meters above the ground. The pace of the average soldier is 0.75 meter.

Perform the following procedures for the pace method:

  • Stand at the bottom of the slope with head and eyes level.
  • Sight a spot on the slope. This spot should be easily identifiable. If it is not, another member of the team should go forward to mark the location.
  • Walk forward and stand on the marked spot. Record the number of paces. Repeat this procedure until you reach the top of the slope (estimate fractions of an eye level).
  • Compute the vertical distance by multiplying the number of sightings by the eye-level height (1.75 meters). Compute the horizontal distance by totaling the number of paces and converting them to meters by multiplying by 0.75 (or the known pace-to-meter conversion factor).
  • Calculate the percent of slope by substituting the values into the percent-of-slope formula (see Figure 5-9). Because this method considers horizontal ground distance and incline distance as equal, you can obtain reasonable accuracy only for slopes less than 30 percent. This method requires practice to achieve acceptable accuracy. A line level and string can be used to train this method.

Figure 5-9. Pace method to determine percent of slope

Angle-of-Slope Method

The angle-of-slope method is a quick way to estimate the percent of slope. The angle of slope is first measured by using an elevation quadrant, an aiming circle, an M2 compass, or binoculars with a standard reticle. If the instrument used to take the angle of measurement is mounted above ground level, the height difference must be compensated for by sighting above the slope a corresponding, equal distance. (The corresponding distance is the distance the instrument is above the ground.) You must conduct the angle of measurement at the base of the slope. Once you obtain the angle of measurement, refer to Table 5-2 and enter the column corresponding to the measured angle of slope. You can read the percent of slope directly from Table 5-2 (see Figure 5-10).

Table 5-2. Conversion of degrees and mils to percent of slope

Degrees of Slope

Mils of Slope

Percent of Slope

1

18

1.7

2

36

3.5

3

53

5.2

4

71

7.0

5

89

8.7

10

175

17.6

15

267

26.7

20

356

36.4

25

444

46.6

30

533

57.7

35

622

70.0

40

711

83.9

45

800

100.0

50

889

108.7

55

978

117.6

60

1,067

126.7

Figure 5-10. Angle-of-slope method to determine percent of slope

SLOPE SYMBOL

Most vehicles negotiating slopes of 7 percent or greater for a significant distance will be slowed. Such slope characteristics must be accurately reported. The symbols illustrated in Figure 5-11 are used to represent various slopes.

Figure 5-11. Percent-of-slope symbols

DESCRIPTION OF SLOPE SYMBOLS

A single arrowhead along the trace of a route pointing in the uphill direction indicates a grade of at least 5 but less than 7 percent. Two arrowheads represent a grade of at least 7 but less than 10 percent. Three arrowheads represent a grade of at least 10 but less than 14 percent. Four arrowheads represent a grade of 14 percent or more. A symbol is not required for slopes less than 5 percent.

The percent of slope is written to the right of the arrow. When the map scale permits, the length of the arrow shaft will be drawn to map scale to represent the approximate length of the grade.

NOTE: Slopes of 7 percent or greater are obstructions to traffic flow and are indicated by the abbreviation "OB" in the route-classification formula.

CONSTRICTIONS

Reductions in traveled-way widths (constrictions) include narrow streets in built-up areas, drainage ditches, embankments, and war damage. These constrictions may limit vehicle movement; therefore, the physical dimensions of the vehicles that will be using the route must be known and considered when conducting the route classification.

Constrictions in the traveled-way width below minimum requirements are depicted on maps and overlays by two opposing shaded triangles. The width of the usable traveled way (in meters) is written next to the left triangle. The length of the constriction (in meters) is written next to the right triangle (see Figure 5-12).

Figure 5-12. Route-constriction symbol

NOTE: Constrictions of traveled-way widths below the minimum standard for the type and flow of traffic are obstructions and are indicated by the symbol "OB" in the route-classification formula.

UNDERPASSES

An underpass is depicted on a map or overlay by a symbol that shows the structure's ceiling. It is drawn over the route at the map location. The width (in meters) is written to the left of the underpass symbol, and the overhead clearance (in meters) is written to the right of the underpass symbol (see Figure 5-13).

Figure 5-13. Underpass symbols

If sidewalks permit emergency passage of wider vehicles, the sidewalks are symbolically represented. This information should be noted on DA Form 1250. The traveled-way width is recorded first, followed by a slash, then the structure's total width, including sidewalks.

NOTE: Items such as arched ceilings or irregularities in ceilings that result in a decrease in overhead clearance must be noted. In such cases, an extension of width may not mean that the structure will accommodate wider vehicles.

Both minimum and maximum overhead clearances, if different, will be recorded. The minimum will be recorded first, followed by a slash, then the maximum overhead clearance.

TUNNELS

A tunnel is an artificially covered (such as a covered bridge or a snowshed) or underground section of road along a route. A tunnel recon determines essential information such as the serial number, location, type, length, width (including sidewalks), bypasses, alignment, gradient, and cross section. A tunnel consists of a bore, a tunnel liner, and a portal. Common shapes of tunnel bores (see Figure 5-14) are semicircular, elliptical, horseshoe, and square with an arched ceiling.

Figure 5-14. Types of tunnel boxes

TUNNEL SYMBOL

Basic tunnel information is recorded on maps or overlays using symbols (see Figure 5-15). The location of the tunnel entrance is shown on a map or overlay by an arrow from the symbol to the location of the entrance. For long tunnels (greater than 30.5 meters), both tunnel entrance locations are indicated.

Figure 5-15. Tunnel symbols

For later reference, a serial number is assigned to each tunnel. (Check for an existing fixed serial number on the actual tunnel or map sheet; if there is not a serial number, assign a number based on the unit's SOP.) Serial numbers are not duplicated on any one map sheet, overlay, or document. The number is recorded inside the symbol. The traveled-way width is shown in meters and is placed below the symbol.

If sidewalks permit the emergency passage of wider vehicles, then the sidewalks are symbolically represented and the traveled-way width is written first, followed by a slash, then the total width including the sidewalks.

NOTE: Structures with arched or irregular ceilings will decrease overhead clearance. An extension of width does not always mean that the structure will accommodate wider vehicles.

OVERHEAD CLEARANCE

Overhead clearance is the shortest distance between the surface of a traveled way and any obstruction vertically above it. The measurement of overhead clearance must be accurate. Obtain the measurements shown in Figures 5-16 and 5-17 and record them on DA Form 1250.

Figure 5-16. Overhead-clearance measurements

Figure 5-17. Dimensions required for tunnels

TUNNEL RECONNAISSANCE REPORT

The following are explanations for sections of DA Form 1250 that are not self-explanatory (see Figures 5-18 through 5-19a):

  • Block 8. Record the tunnel number found on the map sheet or on the head wall (or data plate) of the actual tunnel. If there is not a number on the map or tunnel, then assign an appropriate number based on the unit's SOP. If there is a different number on the map than on the tunnel, record both serial numbers.
  • Block 13. Record the number of railroad tracks passing through the tunnel, if applicable.
  • Block 15. Record the vertical clearance (the shortest clearance from the road surface in the tunnel to the lowest point on the ceiling above the traveled way). Also, record the distance from the sidewalk to the ceiling if traffic can travel on the sidewalks.
  • Block 15 (continued). Record the horizontal clearance. It is the roadway width or the roadway width and sidewalks/emergency lanes (where vehicles can move through the tunnel without striking the top or sides).
  • Block 16. Record the internal tunnel grade. Record the grade of the tunnel entrances in Block 27.
  • Block 17. State whether the tunnel is straight or curved. Record curves that may restrict traffic flow.
  • Block 19. Record a description of what the tunnel entrances (portals) look like and their composition.
  • Block 22. Mark the applicable box. Some tunnels are chambered for demolition. This means that the tunnel has predesigned locations for placing demolitions to destroy the tunnel and deny use by the enemy.
  • Block 23. Record the date the tunnel was constructed.
  • Block 29. Inspect the rock or soil at the tunnel's entrances. If there is a chance of a rock or mud slide, record the location and possible solution to the problem.

Figure 5-18. Sample Tunnel Reconnaissance Report (front)

Figure 5-19. Tunnel Reconnaissance Report (back)

Figure 5-19a. Portal view of tunnelTunnel symbols

STREAM RECON

A stream-crossing site is a location at a body of water where vehicles can "swim" across and not touch the bottom. Identify and report locations that permit smooth traffic flow and reduce route obstructions as much as possible. When conducting a recon of a stream-crossing area, record the stream's depth, width, approaches, velocities, and natural and man-made obstacles (see Figure 5-20).

Figure 5-20. Dimensions required for streams

MEASUREMENTS

Stream depth is usually measured using field-expedient devices such as poles or weighted ropes. Measure the depth every 3 meters along the planned stream-crossing route. Recheck depths and currents frequently during inclement weather. As a result of sudden, heavy rainfall, a sluggish stream or river may become a torrent very quickly, particularly in tropical and arid regions. Monitor weather reports of the surrounding area. Storms occurring miles away can cause flash flooding. Always consider the importance of upstream dams and locks that may cause elevated levels or flooding when opened or destroyed. NOTE: The actual depth you measure is recorded as normal depth when there is little time to recon.

PREEXISTING DATA

In developed areas of the world, special water-navigation maps containing water-body data are available through government agencies. The S2 can obtain copies of such maps. However, always check the actual site when possible; there is no substitute for an actual recon.

STREAM WIDTH

Determine the stream width by using the compass method; an aiming circle, azimuth indicator, or alidade; or a GPS or by taking a direct measurement.

Compass Method

Determine stream width by using a compass to take an azimuth from a point on the near shore and close to the water's edge to a point on the opposite shore and close to the water's edge (see Figure 5-21). On the near shore, establish another point that is on a line and at a right angle to the azimuth selected. The azimuth to the same point on the far shore is + or - 45 degrees (800 mils) from the previous azimuth. Measure the distance between the two points on the near shore. This distance is equal to the distance across the stream.

Figure 5-21. Measuring stream width with a compass

Aiming Circle, Azimuth Indicator, or Alidade

Use an aiming circle, azimuth indicator, or alidade to measure the angle between two points that are a known distance apart on the near shore and a third point directly across the river from one of these points (see Figure 5-22). Using trigonometric relationships, compute the distance across the stream.

Figure 5-22. Measuring stream width with a surveying instrument

Global Positioning System

Calculate the distance using two known grid points (from the GPS).

Direct Measurement

Measure short gaps with a tape measure or a dark rope that is marked and accurately measured.

CURRENT VELOCITIES

Current velocities vary in different parts of a stream. Velocity is usually slower near the shore and faster in the main channel. Perform the following procedure to determine stream velocity:

  • Measure a distance along a river bank.
  • Throw a light floating object (not affected by the wind) into the stream.
  • Record the time of travel it takes for the object to travel the measured distance. Repeat the procedure at least three times. Use the average time of the test in the following formula (see Figure 5-23) to determine the stream's velocity:

Figure 5-23. Finding stream velocity

Stream velocity, in meters per second = measured distance, in meters/ average time, in seconds

STREAM APPROACHES

Gently sloping stream approaches are desirable for fording and swimming operations. Slope is expressed in percent. Ensure that the slope-climbing capability is considered for the vehicles that are expected to ford/swim the stream. This information is found on the vehicle's data plate or dash plate or in the vehicle's technical manual (TM). When considering slope-climbing capability, consider the degrading effects of weather, the condition of the vehicle's tires or tracks, and the condition of the ground surface of both sides of the stream. When bank improvements are necessary, include the amount and type of work on DA Form 1711-R. See Appendix D for further details on engineer reconnaissance and DA Form 1711-R. A blank DA Form 1711-R is provided at the back of this publication; it can be locally reporduced on 8 1/2- by 11-inch paper.

Consider and avoid the following obstacles during stream-crossing operations:

  • High, vertical banks.
  • Mines and booby traps that are located at the entrance and exit or at likely approaches, submerged, or attached to poles and floating logs.
  • Debris and floating objects such as logs and brush, poles, or floating logs with wire attached (which will foul propellers and suspension systems).
  • Ice crusts.

FORDS

A ford is a location in a water barrier where the current, bottom, and approaches allow personnel and vehicles and other equipment to cross and remain in contact with the bottom during crossing. Fords are obstructions to traffic flow and are shown by the abbreviation "OB" in the route-classification formula (detailed information is recorded on DA Form 1251).

During high-water periods, low-water bridges are easily confused with paved fords because both are completely submerged. It is important to know the difference between this type of bridge and a paved ford because of corresponding military load limitations.

Fords are classified according to their crossing potential (or trafficability) for pedestrians or vehicles. Fordable depths for vehicular traffic can be increased by suitable waterproofing and adding deep-water fording kits. These kits permit fording depths up to an average of 4.3 meters. Check vehicle TMs for further fording information.

Record the composition of the approaches. They may be paved or covered with mat or trackway, but they are usually unimproved. The composition and the slope of the approaches to a ford should be carefully noted to determine the trafficability after fording vehicles saturate the surface material of the approaches. Identify the ford's left and right approaches when looking downstream.

Record the current velocity and the presence of debris to determine their effect, if any, on the ford's condition and passability. Estimate the current as--

  • Swift (more than 1.5 meters per second).
  • Moderate (1 to 1.5 meters per second).
  • Slow (less than 1 meter per second).

The ford's stream-bottom composition largely determines its trafficability. It is important to determine whether the bottom is composed of sand, gravel, silt, clay, or rock and in what proportions. Record whether the ford's natural river bottom has been improved to increase the load-bearing capacity or to reduce the water depth. Improved fords may have gravel, macadam, or concrete surfacing; layers of sandbags; metal screening or matting; or timber (corduroy) planking. Note if there is material nearby that may be used to improve the ford. Record limited ford information (such as the following) on maps or overlays using a symbol as shown in Figure 5-24.

Figure 5-24. Ford symbols

  • The ford's geographic location is shown by an arrow from the symbol to the ford location on a map or overlay. The symbol is drawn on either side of the stream.
  • A serial number is assigned to each ford for reference (if the map sheet has a preassigned serial number, use it). Follow the unit's SOP in assigning serial numbers. They must not be duplicated within any one map sheet, overlay, or document.
  • The type of ford is determined by bottom conditions, width, and water depth. Use the letters "V" for vehicular or "P" for pedestrian to show the ford type. Approaches are not considered in determining the ford type.
  • The stream's normal velocity is expressed in meters per second. Seasonal limiting factors follow the stream-velocity notation and are shown by the letters--

-- X = no seasonal limitations except for sudden flooding of limited duration (such as flash floods).

-- Y = serious, regular, or recurrent flooding or snow blockage. NOTE: If the Y symbol is used, the route type in the route-classification formula automatically becomes type Z.

  • The length of the ford, expressed in meters, is the distance from the near to far shores. The width of the ford is the traveled-way width of the ford's bottom.
  • The nature of the bottom is indicated by the most appropriate letter symbol:

-- M = mud.

-- C = clay.

-- S = sand.

-- G = gravel.

-- R = rock.

-- P = artificial paving.

  • The normal depth is the depth of water at the deepest point, expressed in meters. During a hasty recon, the actual water depth is used.
  • A stream's left and right banks are found by looking downstream. Imagine yourself in the middle of the stream and looking downstream. Your left arm would indicate the left bank and the right arm the right bank. In drawing this portion of the symbol, pay attention to the direction of the stream flow. A difficult approach is shown by irregular lines placed on the corresponding side of the basic symbol.

All elements of the ford symbol are separated by slashes. If you do not know or cannot determine any item of the ford symbol, substitute a question mark for the required information. (Record ford information on DA Form 1251. See Figures 5-25 and 5-26.)

Figure 5-25. Sample Ford Reconnaissance Report (front)

Figure 5-26. Sample Ford Reconnaissance Report (back)

UNDERWATER RECON

In deeper water, divers may have to determine bottom conditions. Diving teams trained and equipped for underwater recons select deep-water fording sites. When the divers cannot easily span the distance between banks, inflatable combat rubber recon craft or bridge-erection boats enter the water at a selected entrance and drop off teams at regular intervals. Unless the area is under enemy fire or observation, the craft remain in the water during the recon and pick up divers when the operation is completed. Helicopters may be used to drop teams in the water or place teams on the far shore if the situation permits. Engineer light diving teams routinely conduct river recons at night.

To assist underwater recon teams in maintaining direction, weighted lines (transverse lines) may be placed across the bottom of the water obstacle. Buoys or other floating objects are attached to the lines to indicate the survey area for the underwater recon team(s). When the current is greater than 1.3 meters per second, underwater recon personnel will have difficulty maintaining a position along the line selected. To assist divers, another transverse line, parallel to the original line and with lateral lines connecting both lines, may be placed upstream.

Bottom conditions are easily determined during periods of good visibility and when the water is clear. However, under blackout conditions or when the water is murky, the recon is much slower because swimmers must feel their way across. If the tactical situation permits, diver's may use underwater lanterns.

Environmental conditions (such as depth, bottom type, tides and currents, visibility, and temperature) have an effect on divers, diving techniques, and equipment. The length of time that divers can remain underwater depends on water depth, time at depth, and equipment used. When conducting a recon in a current, swimmers expend more energy, tire more easily, and use their air supply more quickly. In water temperatures between 73° and 85°F, divers can work comfortably in their swimsuits, but will chill in one to two hours if not exercising. In water temperatures above 85°F, the divers overheat. The maximum water temperature that can be endured, even at rest, is 96°F. At temperatures below 73°F, unprotected divers will be affected by excessive heat loss and become chilled within a short period of time. In cold water, the sense of touch and the ability to work with the hands are affected. Air tanks vary in size and govern how long divers can operate. Extra tanks should be available for underwater recon teams, and the facilities to recharge equipment should be located close enough to respond to team requirements.

Units may develop a river-recon report to transmit important information about the river's location, near- and far-shore characteristics, and river characteristics. A sample report is shown in Figures 5-27 and 5-28.

Figure 5-27. Sample River Reconnaissance Report (front)

Figure 5-28. Sample River Reconnaissance Report (back)

(Chapter 5 Countinued)



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