The Location and Survey Unit is to provide special survey data required by the hydraulic engineer for the design study. The type and presentation format of this data is provided in the Locations Units’ "Hydraulic Survey Guidelines". For specialty or unusual projects the Location Engineer will coordinate with the Hydraulics Unit to identify data requirements during the initial stage of the survey. The hydraulics engineer will supplement the location data with survey and informational data obtained during his field reconnaissance and site visit. Review of the project in the field prior to commencing detailed design is a requirement of the engineer with primary responsibility for the drainage study. The purpose of this field trip in addition to obtaining supplemental survey data is to:

• Visually acquaint the designer with conditions and constraints of the site

• Verify data obtained from other sources

• Identify ponds, lakes, reservoirs and other storage areas which affect discharge rates

• Review existing drainage features and obtain information on performance

• Review potential outlet channels for performance and adequacy

• Identify sediment sensitive areas such as lakes, ponds, and developed stream areas

• Review contributing watershed characteristics

• Review and obtain design information on environmental areas of concern such as wetlands and special fishery streams (State GIS mapping is a good resource)

• Obtain details of size, location, length, material type and condition of existing drainage structures. When existing box culverts are to be extended, top slab and center wall thickness must be obtained.

• Obtain historical flood and other stream flow information such as:(also see channel data collection, Section IX)
  • Maximum and other large flood levels at the study site, as well as up and down stream of the site
  • Dates of these occurrences
  • Very frequent flooding levels (examples: annual, 2 year, 5 year)
  • Channel scour and instability
  • Drift potential, size and quantity
  • Conveyance of existing crossings including roadway overtopping, damage and time of closure
  • Descriptive photographs of site

• Examples of additional survey data and supplemental topographical information:
  • Elevations of flooding
  • Elevation of up and down stream features which could control the design such as buildings, roads, yards, fields and other drainage structures
  • Stream bed elevations a sufficient distance up and down stream to establish local stream gradient
  • Floodplain and channel cross-sections for backwater analysis and channel realignments
  • Development and cover in floodplain for determination of flow resistance and distribution.
  • General description of stream bed and bank materials (clay, silt, sand, gravel, cobble, rock). If extensive rock is visible explore extent by probing on culvert size streams for possible footing.
  • Locate areas where berm ditches are needed.

• Additionally for urban sections:
  • Locate and obtain elevations of low areas back of proposed curb for special pickups
  • Locate small inflow systems such as roof and basement drains.

• Review and obtain the following type information for use in bridge scour analysis:
  • Description of floodplain and channel material. If sand or silt, is it fine, medium or coarse?
  • Observe existing structure for evidence of scour and condition around footings and supports.
  • Verify or obtain channel cross-sections under bridge and at locations at least two bridge lengths up and down stream.
  • Elevation and location of deepest point in channel.
  • If visible, note type and condition of existing foundation.

• Review site conditions and obtain precise limits and classification of wetlands and jurisdictional streams for permit application.

All pertinent data and facts gathered through this field reconnaissance and survey are to be documented on work plans, field notes or other forms suitable for submittal with the final project report. The section of the "Check List for Drainage Study and Hydraulic Design" - Appendix Item B, identified as field study is to be completed prior to completion of the field study.