ABSTRACT

1
ABSTRACT Spearfish Creek flows in a narrow,
incised canyon in the northern Black Hills
resulting in high velocity flows that place
increased stress on channel banks and bottom.
Potential results include damage to existing
roadways and bridges as well as channel widening
and damaged fish habitat. Thus, it would be
desirable to predict locations where increased
bank and/or channel stress would be expected
under varying flow conditions. An approximately
1.6 km reach was surveyed using a laser-digital
transit. Channel cross-sections were measured
every 30 m producing a detailed topographic map
of the channel, banks, and limited floodplains.
Flow modeling was performed using discharges that
were based on current stream-flow and known
historic flood flows. The stream was modeled as
segments, using SMS, where inflow to each segment
occurred at the upstream boundary. The segment
containing Squaw Creek tributary had two inflow
boundaries. Results indicted high stress at
numerous points along the entire stream channel
as a function of river channel morphology. Areas
of concern included sections that contained bends
or narrowing of the channel. Where the highway
was closest to the potential channel scour zones,
damage might be expected under severe flow
conditions causing immediate damage to the
fishery. These results will allow highway
engineers and fisheries personnel to maximize
efforts to sustain existing roadways and to
provide and maintain quality fisheries within
Spearfish Canyon.

• SUBSTRATE CHARACTERISTICS
• Water in Spearfish Creek is super-saturated with
  respect to calcium and magnesium owing to its
  source from the Madison Limestone. Water
  temperature plays a key role in the precipitation
  process since calcium has a decreased solubility
  in cold water. Thus, colder water temperatures
  favor precipitation of the cement rind and warmer
  waters favor weakening and dissolution of the
  cement rind. Rind thickness varies throughout
  the study reach from less than 1/8 to more than
  2 (Fig. 2).
• Consequences of the rind are two-fold
• Cementing of the bottom sediment and subsequent
  reduction in available fish spawning habitat
• Immobility of the sediment at shear stresses
  which would remove it were the cement not
  present
• Thus, determining required shear stress and
  effect sediment mobility had on fish habitat were
  explored.

• PROJECT GOALS
• This project focused on potential effects that
  physical and mechanical channel properties
  (channel substrate, flow conditions, and banks
  and other structures) had on fish habitat. Three
  primary project goals were
• model potential effects of increased discharge
  on fish habitat
• determine behavior of substrate (scour and
  deposition of sediment)
• identify potential locations of increased bank
  stress
• GEOLOGICAL SETTING
• The study area was located approximately 10 miles
  south of the city of Spearfish on Spearfish Creek
  between Homestake Mining Co. (now Barric Mining
  Co.) Hydroelectric Power Plant Number Two (Hydro
  No. 2) and Maurice intake, a diversion tunnel
  supplying Hydro No. 1 in Spearfish (Fig. 1). Two
  streams flow through the study area. Spearfish
  Creek (the larger of the two) originates from
  springs emanating from the Mississippian Madison
  Limestone and flows northward within the confines
  of Spearfish Canyon. Squaw Creek (the smaller
  tributary stream) enters Spearfish Creek about
  1/3 mile below Hydro No. 2 and sources from
  springs and seeps within the Cambrian Deadwood
  formation aquifer east of Spearfish Canyon and
  flows westward. The stream flows north out of
  the Black Hills crossing saturated and
  unsaturated Paleozoic and Mesozoic strata prior
  to emptying into the Belle Fourche River.
  Numerous Tertiary intrusions and other structural
  features, such as faults, also contact the stream
  channel. As a result, net groundwater
  contributions and losses are realized from
  springs and seeps and high permeability zones
  between Hydro No. 2 and Maurice Intake (Table 1).
• Spearfish Creek is a low sinuosity single channel
  within the study reach although it does meander
  through the bedrock of the canyon through which
  it flows. State Highway 14A, located immediately
  to the west of the main channel, is stabilized by
  using gabion structures (wire mesh baskets filled
  with cobbles and boulders) to armor the road side
  channel bank which effectively constrains the
  creek from natural meandering and bank
  adjustments during high flows. Thus, increased
  shear stress generated during high flows would
  primarily be directed toward the gabions and the
  channel bottom promoting scour. Potential loss
  to fish habitat under these conditions would be
  high. In addition, under extreme flow events,
  gabions could easily be washed out causing bank
  and possible road failure, both of which would
  exacerbate loss of fish habitat.

Sediment transport sites shown in Figure 3 and
4. 90 Bend 300 Marker Hydro 2
Locations of discharge measurements shown in
Table 1. A B C
Figure 1. Study reach on Spearfish Creek.
Digital elevation model created using survey
data and SMS (Boss, Int.)
software.
2
Study Methods and results A 3-D numerical flow
model, Surfacewater Modeling System, was used to
evaluate potential effects of various flow
conditions on the banks and substrate of
Spearfish Creek. The model was run on a
topographic base map (Fig. 1) that was prepared
for this study from detailed surveys of the
channel, banks, floodplains, and surrounding
areas (Fig. 5). Head loss along the main channel
of Spearfish Creek was 80ft (4463 ft at Hydro No.
2 to 4383 ft at Maurice intake). Model
limitations for maximum head loss of lt25 ft
forced the study reach to be segmented for flow
analysis. For the study reach, 3 material types
were designated 1) channel, 2) vegetated bank,
and 3) engineered bank. Each of these materials
were assigned an erodibility factor (Manning
roughness coefficient) with in-channel erosion
also controlled through an eddy viscosity value
(transverse flow). Adjustment of parameter
values were based on actual physical conditions
at the stream and from published data. Flow
modeling was performed using the mean average
discharge (60 cfs), or the 50 probability flow
(Fig. 6), and a medium flood event discharge (250
cfs), or a 0.5 probability flow. Results from
the 250 cfs event for the confluence is shown in
Figure 7. The arrows represent flow magnitude
vectors, the larger the arrow, the higher the
velocity. At the upstream edge, flow is spread
across the entire segment and is flowing out of
the main channel. At this location, erosion on
the vegetated and engineered banks is low due to
the velocity slowing due to bank roughness and
vegetation. In the main channel above the
confluence, sediment is securely cemented forming
a mostly impenetrable bottom. flow impinging on
the outer, west-side bank, increases in velocity,
and thus, shear stress as well. A 1994 flood
event had an estimated discharge of 1200 cfs
(based on water elevations and cross-sections)
and undercut and eroded gabion structures along
the entire study reach (Fig. 8). Significant
channel erosion occurred as well as the cement
was broken by the high shear stresses generated
by this magnitude of flow. In 2000, damaged
gabions were removed and portions of the channel
were re-engineered.
Summary These results form a preliminary
assessment of channel and bank erosion for
Spearfish Creek indicate areas of concern exist
from both a fisheries and a highway standpoint.
During increased flow, increased bank stress (and
the potential for bank failures) exists at
several points along the highway side of the
channel. Many of these banks are protected by
gabion structures which in effect, transfers the
stress to the channel bottom which can reduce or
eliminate fish spawning habitat in these areas.
In extreme events, complete failure of the
highway side bank is possible by under-washing of
the gabions.