[Code of Federal Regulations]
[Title 40, Volume 24]
[Revised as of July 1, 2005]
From the U.S. Government Printing Office via GPO Access
[CITE: 40CFR230.45]

[Page 269-270]
 
                   TITLE 40--PROTECTION OF ENVIRONMENT
 
         CHAPTER I--ENVIRONMENTAL PROTECTION AGENCY (CONTINUED)
 
PART 230_SECTION 404(b)(1) GUIDELINES FOR SPECIFICATION OF DISPOSAL 
SITES FOR DREDGED OR FILL MATERIAL--Table of Contents
 
          Subpart E_Potential Impacts on Special Aquatic Sites
 
Sec. 230.45  Riffle and pool complexes.

    (a) Steep gradient sections of streams are sometimes characterized 
by riffle and pool complexes. Such stream sections are recognizable by 
their hydraulic characteristics. The rapid movement of water over a 
coarse substrate in riffles results in a rough flow, a turbulent 
surface, and high dissolved oxygen levels in the water. Pools are deeper 
areas associated with riffles. Pools are characterized by a slower 
stream velocity, a steaming flow, a smooth surface, and a finer 
substrate. Riffle and pool complexes are particularly valuable habitat 
for fish and wildlife.
    (b) Possible loss of values: Discharge of dredged or fill material 
can eliminate riffle and pool areas by displacement, hydrologic 
modification, or sedimentation. Activities which affect riffle and pool 
areas and especially riffle/pool ratios, may reduce the aeration and 
filtration capabilities at the discharge site and downstream, may reduce 
stream habitat diversity, and may retard repopulation of the disposal 
site and downstream waters through sedimentation and the creation of 
unsuitable habitat. The discharge of dredged or fill material which 
alters stream hydrology may cause scouring or sedimentation of riffles 
and pools. Sedimentation induced through hydrological modification or as 
a direct result of the deposition of unconsolidated dredged or fill 
material may clog riffle and pool areas, destroy habitats, and create 
anaerobic conditions. Eliminating pools and meanders by the discharge of 
dredged or fill material can reduce water holding capacity of streams 
and cause rapid runoff from a watershed. Rapid runoff can deliver large 
quantities of flood water in a

[[Page 270]]

short time to downstream areas resulting in the destruction of natural 
habitat, high property loss, and the need for further hydraulic 
modification.

    Note: Possible actions to minimize adverse impacts on site or 
material characteristics can be found in subpart H.