Hydrology and Flow Management
The drainage districts employ a complex computer model to simulate storm water runoff flows, water flow in channels,and water elevations throughout the system during storm events. The ‘design storm’ for the districts is the 100-year storm over a 24-hour period. The hydrology of the drainage districts are affected by many complex variables, such as:
- The pattern of storm events: precipitation volume, duration, timing and frequency
- Soil characteristics: permeability, soil moisture and ground water elevations
- Vegetation: type and area covered
- Impervious surfaces: roads, parking lots, roofs, gravel (compacted, uncompacted), compacted dirt, and area covered
- Channel characteristics of ditches, creeks and the Columbia Slough
- Storm water storage capacities: in-channel, out-of-channel and constructed
- Drainage system infrastructure: culverts, control structures and pumping plants
- Development: the changing characteristics of land use, which affect storm water runoff during and after the development process
An overview of how the MCDD manages Columbia Slough water elevations during seasonal periods is provided below.
Summer Flows (typically June to mid-October)
- Close two 60” slide gates at NE 142nd cross levee
- Water levels maintained at elevation 8.0 – 9.0 feet NGVD – eastern basin
- Maintain elevations by pumping at pump station #4 or metering flows at cross levee – partially open gates, water flows to pump station #1
- Higher water elevations are necessary for irrigation and wetland areas
- Water elevation maintained between 5.0 to 6.0 feet NGVD by pumping at pump station #1, or until the Columbia River elevation drops below elevation 4.5 feet NGVD.
- Gravity flow water into the lower Columbia Slough once the water level of the Columbia River drops below elevation 8.0 feet NGVD
- To maintain lower elevations pumping is needed 10-11 months/year
- Control structure closed early May to fill lake for recreational use
- Water elevation in lake to reach 11.2 feet NGVD before flowing over weir dam
- Control structure reopens early October to drain back to winter elevation 8.5 -11.0 feet NGVD
Winter Flows (typically mid-October through May)
Normal Operating Procedure - Water elevations and pump stations used:
- Pre-storm cross levee remains open unless there are pumping problems at PS #1.
- Pre-storm slough is pumped to elevation 5.5 – 6.5 feet NGVD at PS #1
- Pre-storm slough is pumped to elevation 7.0 – 8.0 feet NGVD at PS #4
- Drawdown allows storage room during any power outages
- During storm water levels maintained between elevations 6.0 – 8.0 feet NGVD at PS #1
- During storm water levels maintained between elevations 8.0 – 10.0 feet NGVD at PS #4
Operation for Debris Removal
Debris removal is an ongoing operation for the drainage districts. The districts’ work with SWINE, Inverness County Jail, Columbia River Corrections, and the Columbia Slough Watershed Council in locating and removing illegally dumped debris. The debris is sorted for recycling and transported to the appropriate disposal facilities. The Metro Disposal Voucher Program works in co-operations with the District for year round clean-up.
Nuisance Animal Control
Beaver and nutria can burrow into the levees, which can lead to a levee breach. Beaver burrow about 10 to 12 feet and build their den. The dens can be anywhere from 12 to 20 feet in diameter and that serves as a conduit for water to go through the levees. The MCDD has an annual permit from the Oregon Department of Fish and Wildlife (ODFW) to control nuisance animals in and around the districts’ waterways. The district employs a licensed trapper for this effort. The districts are required to notify and file reports with the ODFW whenever animal control is used.
Equipment Operations and Spill Containment
All equipment is inspected every morning for hydraulic leaks and repaired, if needed, before the machine can be operated. All work performed on equipment is done in the shop and repair yard, where all fluids and metals are collected and disposed of in a safe manner. Spill containment compartments have been installed in all storage buildings. All trucks and excavating/water-based equipment has a spill containment kit. These kits are inspected on a monthly basis. All employees have been trained as a first responder to deal with small, non-hazardous spills.