A bridge site survey drawing is the foundation of every bridge design project. Before a single structural calculation is run, the survey team must capture a precise picture of the site — the river channel, approach topography, existing utilities, soil conditions, and hydraulic behaviour.
Why Bridge Site Surveys Differ from General Topographic Surveys
A standard topographic survey captures what exists. A bridge site survey goes further — it must capture what the river does: flood behaviour, scour potential, bed material, seasonal water levels, and the hydraulic corridor both upstream and downstream. This data drives foundation type, span length, deck elevation, and scour protection design before the engineer begins calculations.
The Survey Drawing Sheet Set
- Cover / Key Map Sheet — project location, sheet index, general notes, datum and coordinate reference, legend
- Survey Control Sheet — horizontal and vertical control network, benchmarks, traverse points
- Site Plan / Topographic Plan — plan view at 1:500 or 1:1000 showing the full river corridor, approach roads, and proposed bridge axis
- Longitudinal Profile Sheet — river bed and water surface along the bridge centreline, 150m upstream and 75m downstream
- Cross-Section Sheets — sections at the bridge axis, at each abutment, and at regular intervals upstream and downstream
- Soil Boring / Geotechnical Sheet — boring locations on plan, borehole logs, subsurface stratigraphy
- Hydrological / Hydraulic Data Sheet — flood frequency data, water surface elevations, drainage area map
Required Field Data
Control and Reference Data
- Horizontal control: coordinate system, traverse points, GPS control monuments
- Vertical control: datum, minimum two benchmarks on opposite banks
- Ground surface elevation of all existing and proposed drill holes
- Existing survey monuments within 500m of the site
Topographic Data
- Contour survey at 1m interval, covering 200–500m upstream and downstream and 100m beyond each bank
- Spot elevations at all grade breaks, structures, and drainage features
- Existing road alignment and profile for approach roads up to 500m either side
- Location and dimensions of all existing structures
- Vegetation type and extent
- Angle of skew if the bridge crosses the waterway at an angle
River and Waterway Data
- River bed profile along the bridge centreline
- At least three cross sections of the stream — one at or near the centreline and one at each end of the stream profile
- Normal water level (NWL), low water level (LWL), and high flood level (HFL) with dates
- Bed material description and particle size
- Evidence of meandering, bank erosion, or channel migration
- Drainage area upstream of the bridge site
Geotechnical Data
- Boring at each critical foundation element location
- Borehole logs with soil classification, stratigraphy, and rock depth
- Groundwater level at time of boring and estimated seasonal range
- Standard penetration test (SPT) results or equivalent
Hydraulic and Hydrological Data
- Catchment area delineation and area measurement
- Flood frequency analysis (2-year, 10-year, 50-year, 100-year return periods)
- FEMA flood zone designation if applicable
- Manning’s n roughness values for channel and floodplain
Existing Infrastructure
- All underground utilities within the survey corridor
- Overhead lines with vertical clearances
- Existing bridge or culvert dimensions, condition, and foundation type
- Adjacent property boundaries and ownership
Legend — Bridge Site Survey Symbols
| Category | Symbol | Description | Style |
|---|---|---|---|
| Control | BM-1 (triangle) | Benchmark, vertical control | Orange triangle, elevation label |
| Control | CP-1 (circle+cross) | Horizontal control point | Circle with cross, coordinates |
| Control | + 48.250 | Spot elevation | Cross with elevation, 0.3mm |
| Control | CL dash-dot | Bridge centreline / axis | Long dash-dot, 0.7mm |
| Waterway | NWL dashed | Normal water level | Blue dashed, 0.2mm |
| Waterway | HFL dash-dot | High flood level | Red dash-dot, 0.2mm |
| Waterway | LWL dotted | Low water level | Blue dotted, 0.15mm |
| Waterway | Bank line | River bank top edge | Solid blue, 0.35mm |
| Waterway | Flow arrow | Direction of flow | Arrow along channel |
| Waterway | XS-1 dashed | Cross-section cut line | Grey dashed, 0.2mm |
| Topography | Minor contour | 1m or 0.5m interval | Green thin dashed, 0.15mm |
| Topography | Index contour | 5m or 10m labelled interval | Green medium, 0.25mm |
| Topography | Property line | Land boundary | Heavy solid, 0.7mm |
| Topography | ROW line | Road right-of-way | Dotted, 0.2mm |
| Structure | ABT-L / ABT-R | Left and right abutment | Heavy rectangle, brown fill |
| Structure | P1, P2 | Bridge pier (proposed) | Solid filled rectangle |
| Geotechnical | BH-1 (circle) | Borehole location | Circle with cross, brown |
| Geotechnical | TP-1 (X mark) | Test pit location | X symbol, labelled |
| Utilities | W | Water main | Solid blue, W label repeated |
| Utilities | G | Gas main | Dashed yellow, G label |
| Utilities | SS | Sanitary sewer | Dashed brown, SS label |
| Utilities | E | Underground electric | Dashed red, E label |
| Utilities | OHE | Overhead electric line | Solid with pole symbols |
CAD Layer Setup
| Layer | Description | Colour | Weight |
|---|---|---|---|
| C-SURV-CTRL | Survey control and benchmarks | Orange | 0.35mm |
| C-TOPO-MAJR | Major index contours | Green | 0.25mm |
| C-TOPO-MINR | Minor contours | Lt green | 0.15mm |
| C-WATR-BNKL | River bank lines | Blue | 0.35mm |
| C-WATR-LEVL | Water level lines NWL/HFL/LWL | Blue/Red | 0.20mm |
| C-BRDG-AXIS | Bridge centreline | Black | 0.70mm |
| C-BRDG-ABUT | Abutments proposed | Brown | 0.70mm |
| C-BRDG-PIER | Piers proposed | Grey | 0.50mm |
| C-GEOT-BORH | Borehole locations | Brown | 0.35mm |
| C-PROP-LINE | Property and ROW boundaries | Magenta | 0.70mm |
| C-ANNO-TEXT | General annotations | Black | 0.18mm |
Survey Scales
The topographic map is plotted at 1:500 with 1m contour intervals. The longitudinal section is drawn at 1:50 vertical and 1:500 horizontal. Cross sections are drawn at 1:100 with data taken at 20m intervals upstream and downstream of the bridge axis.
Free CAD Resources
Several sources provide free DWG files for bridge survey drawings. dwgmodels.com/bridges hosts AutoCAD bridge drawings including plan views, sections, and structural details. caddetails.com provides bridge CAD details in 2D and 3D formats. Always verify the licence terms before using downloaded files commercially.
Conclusion
A bridge site survey drawing set must capture the physical site, the hydraulic behaviour of the waterway, subsurface conditions, and existing infrastructure in a single coordinated package. Get the control right, shoot every cross section the hydraulic analysis will need, and document water levels with dates — those are what reviewers check first.