8195

• UCREFRP Catalog Number: 8195
• Author: Richter, B. D., J. V. Baumgartner, J. Powell and D. Braun
• Title: A Method for Assessing Hydrologic Alteration within Ecosytems
• USFW Year: 1996
• USFW - Doc Type: Conservation Biology
• Copyright Material: YES

Richter et al. Assessing HPdrologicAlteration 1171
Table 2. Results of the Indicators of Hydrologic Alteration analysis for Roanoke River at Roanoke Rapids, North Carolina.

HA group
Streamflouf'
(m•1/sec)
Pre- Post-
impact impact Means

Deviation'
magnitude/"%

onfidence limits
(lots-high)

re-
impact

Coefficients of variation
Post- Deviation' Confidence limits
impact magnitude/"?. (low-high)
Group 1: Monthly magnitude
October 162 .166 4/3 -58-66 0.90 0.70 -0.17/-19 -0.36-0.02
November 156 184 28/18 -19-75 0.56 0.60 0.04/7 -0.10-0.17
December 225 211 -14/-6 -71-43 0.62 0.48 -0.14/-23 -0.27--0.01
January 337 270 -67/-20 -149-1 0.64 0.44 -0.21/-32 -0.34--0.07
February 350 293 -57/-16 -119-7 0.40 0.42 0.02/5 -0.08-0.12
March 361 303 -58/-16 -139-22 0.47 0.56 0.09/19 -0.03-0.21
April 314 315 1/0 -76-79 0.37 0.64 0.27/72 0.15-0.39
May 222 296 74/33 4-144 0.43 0.62 0.20/46 0.07-0.32
June 184 206 22/12 -2-65 0.47 0.48 0.01/3 -0.10-0.12
July 195 156 -39/-20 -93-14 0.68 0.62 -0.05/-8 -0.21-0.16
August 201 150 -51/=26 -118-15 0.97 0.39 -0.58/-60 -0.75--0.41
September 164 150 -17/-10 -71-37 0.90 0.49 -0.41/-45 -0.57--0.24
Group averages` 15% 28%
Group 2: Magnitude and duration of annual extremes
1-day minimum 45 28 -17/-37 -23--11 0.39 0.20 -0,750 -0.27--0.13
3-day minimum 48 40 -8/-16 -15-0 0.39 0.28 -0.11/-28 -0.19--0.03
7-day minimum 51 55 4/7 -4-12 0.39 0.29 -0.10/-24 -0.17--0.01
30-day minimum 68 81 13/19 1-24 0.34 0.31 -0.03/-8 -0.11-0.05
90-day minimum 116 125 9/7 -11-28 0.40 0.30 -0.10/-25 -0.18--0.02
1-day maximum 2209 602 -1607/-73 -1958--1256 0.47 0.30 -0.17/-36 0.26--0.08
3-day maximum 1924 581 -1343/-70 -1650--1038 0.47 0.32 -0.15/-32 -0.25--0.06
7-day maximum 1338 552 -786/-59 -1002--572 0.46 0.36 0.10/-22 -0.20-0.00
30-day maximum 633 477 -156/-25 -250--63 0.30 0.44 0.14/47 0.05-0.23
90-day maximum 423 363 -60/-14 -121-79 0.25 0.42 0.17/70 0.09-0.25
Group averages` 21% 34%
Group 3: Timing of annual extremes
Julian date of annual
, minimum 264.0 360.7 96.7/37 75.7-117.6 0.17 0.12 -0.05/-29 -0.08--0.02
Julian date of annual
maximum 71.9 137.8 65.9/92 17.7-114.1 0.72 0.70 -0.78/-53 -1.05--0.51
Group averages` 65% 41%
Group 4: Frequency and duration of high and low pulses
Low pulse count 11.0 36.4 25.5/232 21.4-29.4 0.43 0.29 -0.13/-31 -0.22--0.05
High pulse count 15.6 22.7 7.1/45 4.1-10.1 0.28 0.34 0.06/23 -0.01-0.14
Low pulse duration 7.4 3.2 -4.2/-57 -5.5--3.0 0.48 0.36 -0.12/-25 -0.22--0.02
High pulse duration 6.0 4.9 -1.1/-18 -2.3-0.1 0.41 0.51 0.10/24 -0.01-0.21
Group averages` 88% 26%
Group 5: Rate and frequency of change in conditions
Fall rate -55.1 -59.6 -4.5/8 -11-2 -0.27 -0.21 0.06/-21 0.00-0.11
Rise rate 90.0 60.2 -29.8/-33 -39--20 0.29 0.18 -0.11/-38 -0.17--0.05
Fall count 67.7 90.9 23.2/34 19.8-26.6 0.11 0.88 -0.03/-30 -0.06--0.01
Rise count 60.9 91.6 30.7/50 27.0-34.4 0.14 0.07 -0.07/-50 -0.10--0.05
Group averages` 31% 35%
"Daily mean streamflotvs in cubic meters per second.
'The deviations represent the Indicators of Hydrologic Alteration.
`Group averages are computed as the tnean of all deviations (in absolute values) upithin the group
of hydroelectric power at Roanoke Rapids Lake. An ob-
vious impact of flood control operations on the Roanoke
is the virtual elimination of high-magnitude flooding
(Fig. 4). Floods in excess of 8500 cros (- 30,000 cubic
feet per second) occurred in only five of the post-clam
years, whereas floods greater than this size occurred in
every pre-dam year. Multi-day maxima are likewise af-
fected by the flood-control operations (Table 2).
The pulsing behavior of the Roanoke River has been
severely affected because both high and especially low
pulses (Fig. 5) now occur with substantially greater fre-
quency. The average duration of pulses, on the other
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