HISTORY AND BACKGROUND

River Influenced City - City Influenced River

The Smoky Hill River is an integral part of the City of Salina's history - from power, navigation, local commerce, recreation and travel, the river has had a major impact on the city. However, due to a growing population and increased infrastructure development, the river has been impacted. 

In 1951, the City of Salina saw a 500-year flood event. After the Federal Levee System was established, 6.8 miles of perennial river channel flow through downtown was cutoff. The original Flood Risk Management plans included provisions to maintain nominal flow in the Old Channel for potable water and flood attenuation through the intake structure. 

In 2010, the City of Salina approved the Smoky Hill River Master Plan after soliciting public input. The project was converted from a CAP Section 1135 to a General Investigations Study in July 2024. 

THE PROBLEM

Loss of natural flow regime:

Diversion of the Smoky Hill River into the 1.1-mile cut-off channel resulted in loss of a natural flow regime and sediment transport function in the Old Channel. Before the cut-off channel, the Old Channel would have received runoff from 8,341 square miles of drainage, contributing 80,000 acre-feet of water annually. Currently, the Old Channel receives run-off from a 4.6 square mile urban drainage that contributes 6,300 acre-feet of runoff. Current flow is insufficient for maintaining quality aquatic and riparian habitat. 

Sedimentation in Old Channel: 

The upstream culvert is filled entirely with sediment and inhibits free discharge of flows (only 1-2 cfs of water seeps through.) Reduced flow has caused sedimentation, which further reduces channel capacity and flow rates. It's easy for sediment to deposit because reduced flows can't remobilize sediment and the channel has a very mild slope. Sedimentation has degraded stream habitat function and features, including loss of stream flow areas, loss of stream depth and loss of riffle/pool sequences. Sediment deposition upstream of the weir is about seven feet deep. 

Loss of quality habitat and connectivity: 

Aquatic, wetland and riparian habitat features have been degraded or eliminated by loss of flow and sedimentation. Floodplain encroachment and development has had an adverse impact on habitat and connectivity, resulting in loss of riparian forest and off-channel emergent wetland habitats. There is currently limited connectivity between the wetlands and Lakewood Lake and the Old Channel, which has resulted in loss of aquatic passage. 

FUTURE WITHOUT PROJECT CONDITIONS

• Continued lack of flow within the Old Channel from FRM project (1-2 cfs below South Ohio Street culvert.)
• Emergent wetland and in-stream aquatic habitat quality and quantity will continue to be low and degrade.
• Old Channel will continue to have poor water quality, will support little aquatic life, offer no aquatic habitat, and have channel and bank erosion.
• Regional analyses indicate that future weather patterns will be more variable resulting in the potential for more extreme droughts and precipitation events.

PROBLEM MEASURES

Sediment capture:

• Sediment Forebay
  • Construct sediment forebay near the upstream end of the Old Channel.
  • Designed to slow incoming water and facilitate capture of coarser particles.
  • Bottom-hinged crest gate to help manage sediment delivery to restored channel. Diverts water from the top of the water column.
  • Periodic cleanout required.
• Benefits
  • Isolates sediment to an accessible location to facilitate easy access for maintenance and removal.
  • Prolong the life of the project and reduce future Old Channel sedimentation.
  • Beneficial ecological functions.
  • City also discontinuing use of sand to streets and installing devices to capture trash. 

Wetland habitat:

• Old Channel Connected Wetlands
  • 1.7 acres of connected wetland shelves.
• Lakewood Lake Wetlands
  • 35-36 acres of emergent wetland.
• Benefits
  • Provides habitat for wildlife, flood storage, pollution filtration and enhance water quality, and opportunities for recreation.
  • Beneficial ecological functions.

Stream and habitat connectivity: 

• Remove Western Star Mill Weir
  • Replace with 5 step pools.
  • Step pools composed of channel-spanning pools with boulder or cobble steps.
  • Convey flow all year round to ensure fish passage through pools.
• Benefits
  • Restores aquatic life connectivity and passage in Old Channel.
  • Moderates slope difference and allows for aquatic passage.
  • Steps allow fish to move from one pool to the next.