CON/SPAN® i-Series™

CON/SPAN® i-Series™

An ecological four-sided culvert. The CON/SPAN i-Series Culvert provides and maintains a natural streambed with its engineered and tested invert technology. It stands apart from traditional culverts that are typically designed to pass flood discharge without consideration for stream ecology impacts.

Find your local Contact

Our local contacts are experts who are ready to help

A legacy of innovative technologies is blended into the CON/SPAN i-Series, an ecologic hyporheical culvert.

There are over 10,000 CON/SPAN installations since 1983. CON/SPAN Bridge Systems have been used by more state DOTs than any other system.

With a history of innovation and experience, Contech has taken precast culverts to the next level with the CON/SPAN® i-Series. Integration of the i-Series invert technology promotes sedimentation of natural streambed material. This creates a natural bottom, open to the hyporheic zone below.  The engineered bottom enhances the stream biology and ecology as well as provides areas of low velocity to allow for fish passage through the culvert. Spans range from 12’ to 24’.

Benefits of the CON/SPAN i-Series System:

  • The i-Series™ allows design engineers to HARMONIZE the biological interests of the fish with the hydraulic requirements of a culvert installation.
  • Stream-simulated Culvert Design – Meets expected outcomes of a successful stream-simulated culvert design, including flood conveyance, fish passage, profile continuity, hydraulic diversity, sediment transport continuity, low flow continuity, margin habitat, debris transport, connectivity to the subgrade (hyporheic zone).  See chart below for comparison to traditional culverts.
  • Modular Culvert System - Rapid installation results in reduced overall project costs, delays and detours.
  • Designed “Site Specific” - Meets your site needs in full compliance with AASHTO design standards for highway use.
  • PROVEN Design Methodology – extensive testing performed at Colorado State University
  • Total Reliability

Industry Research & Comprehensive Testing

The Washington State Department of Fish and Wildlife (WDFW) published a stream-crossing guideline which enumerates nine expected outcomes of a successful stream-simulation culvert design. Hyporheic connectivity differentiates the ecological bottom culvert from traditional culvert options. Of these ten outcomes, nine are expected to be fulfilled by the ecological invert technology, as supported by the results of the testing program (available upon request). The tenth outcome, bed gradation continuity, can be achieved by manual filling of the culvert at installation with natural bed sediments.

Successful Culvert Design Outcomes

  • Flood conveyance is the ability for the culvert to pass the required design flood.
  • Fish passage is the ability for fish to have appropriate resting areas to allow migration through the culvert.
  • Profile continuity is the preservation of the reachwise stream slope through the culvert. Maintaining slope is achieved by maintaining a natural bed through the culvert which reflects changes in the upstream and downstream reaches, and preventing outlet perching and degradation of the bed inside the culvert.
  • Hydraulic diversity is the presence of zones of low, zero, or negative (upstream) flow velocities within the culvert along with regions of higher velocities. These zones provide resting habitat for aquatic organisms inside the culvert.
  • Sediment transport continuity means that bed material transported through the upstream reach is continuously supplied to the culvert bed and supplied by the culvert to the downstream reach at an equivalent rate, allowing the culvert to reflect the bed structure of the stream reach.
  • Low flow continuity is the maintenance of a channel for fish passage during low-flow events.
  • Margin habitat is the existence of areas of low velocity and turbulence along and near the banks of a stream where fish, especially juveniles, can use for migration. In the ecological bottom culvert, it is a consequence of developing a low-flow channel in the culvert.
  • Debris transport is the ability for the culvert to pass large woody debris or miscellaneous detritus.
  • The hyporheic zone is the region beneath and alongside the streambed where there is interaction between the groundwater and the surface water. The hyporheic zone provides ideal habitat for microbes and invertebrates which are critical to the overall health of the stream.
  • Bed gradation continuity is the maintenance of a bed material grain size distribution through the culvert which is equivalent to the grain size distribution of bed material upstream and downstream of the culvert. This criteria can be addressed by manual filling of the culvert at installation with natural bed sediments.
Successful Culvert
Design Outcomes
i-Series™ Culvert Traditional Culvert w/ Invert
(may include buried invert)

Flood Conveyance

Fish Passage

Profile Continuity

Hydraulic Diverity

Transport Continuity

Low Flow Continuity

Margin Habitat

Debris Transport

Connectivity to Subgrade
(hyporheic zone)

Bed Gradation Continuity


Technical information for this product is centrally located in the technical guides section.

Technical Guides

The Contech Advantage

Agency/Regulatory Guidance

Our team is ready to provide you with expert advice and assistance on local regulatory requirements, resulting in faster approvals.


Solution Development

Our engineers can review your requirements, weigh all options, and recommend the optimal solution to integrate with your site designs.

Technical Expertise

Our engineers can assist by providing product specific engineering calculations such as hydraulics, buoyancy, foundation reactions, and unit sizing.

Cost Estimates

We can quickly provide engineer’s cost
estimates to assist with your solution
selection process.

Site Specific Drawings

Our engineers can provide site-specific drawings for proposals, project meetings, and submittals, helping you be more efficient with your time.

On-site Assistance

Contractors know time is money, so we provide preconstruction meetings, delivery coordination, and on-site installation support to ensure a timely, smooth installation.