Hydraulic Design of
Stepped Spillways
James Ruff 
and 
Jason Ward 
Project Background 
* Continuation of Dam Safety Research 
- Cooperative agreement between CSU & USBR 
- spillway overtopping flows 
- near prototype scale test facility 
* Stepped Spillway Phase 
- Start of construction July 1999 
- Two summers of testing 
- Data analysis and report 2000-2001 
Overtopping Facility 
* Near-prototype scale 
* 2H:1V Slope 
* 100 ft concrete chute 
* 50ft height 
* 10ft wide 
 reduced to 4 ft 
* 5 ft deep 
 7 ft extended height 
* Horsetooth water supply 
approx. 120 cfs max 
Objective 
Collect data on the characteristics of stepped spillway 
flow and develop a hydraulic design procedure. 
Experimental Program 
* Air concentration data 
* Velocity data 
* Visual Observations 
* Range of discharges & locations 
* Two step heights 
Test Series 
Stepped Spillway Tests 
* Horizontal Steps 
* Constructed of lumber and 
plywood 
Smooth Spillway Tests 
* Steps removed 
* Comparison data 
* First Series 
- 4 ft tread length 
 2 ft riser height 
- 25 two-foot steps 
* Second Series 
- 50 two-foot steps 
- 2 ft tread length 
 1 ft riser height 
* Third Series 
 Steps removed 
 Comparison data 
4
Flow Classification 
Nappe Flow 
Skimming Flow 
Observations 
h = 2.0 ft 
Transition 
Q = 40 cfs 
Window # 4 
Nappe 
Q = 20 cfs 
Window # 4 
Skimming 
Q = 60 cfs 
Window # 3 
5
Observations, contd 
h = 1.0 ft 
Nappe 
Q = 7.1 cfs 
Window # 2 
Skimming 
Q = 21 cfs 
Window # 2 
h = 1.0 ft 
Q = 60 cfs 
6
Friction Factor 
Darcy Friction Factor f versus k/dw 
f 10.00 1.00 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 
DE/Eo h = 1 ft h = 2 ft smooth eqn. (6-21) f = 0.30 eqn. (6-21) f = 0.25 eqn. 
(6-21) f = 0.079 0.020.040.060.080.0100.0 Present Study, h = 1ft Present Study, 
h = 2 ft Gaston (1995) Chamani et. al. equation (2-23) Present Study, smooth (k 
= 0.01 ft) Chamani et. al. (1999) Tozzi equation (2-16)equation (6-16) 8S gd wf1 
dw 15.2 log 85. 0 k = roughness height dw = clear water depth avg 
Energy Dissipation, contd 
Energy Dissipation versus Nh/yc 
Nh/yc 
Energy Dissipation 
f 3 cosq 1 f 3
1 sin 8 q 2 sin 8 q
DE Eo E1 E Nh 3 o 
N = number of steps oo y 2 
h = step height
yc = critical depth
Hydraulic Design Procedure 
* Assume given information 
- Total discharge, Q 
- spillway width, b 
- spillway height, H 
- spillway slope, q = 26.6 
- select step height, h (1.0 ft or 2.0 ft) 
* Design Charts: 
- friction factor f = f (H, q) versus Nh/yc 
- bulking coefficient e = f (H,q) versus Nh/yc 
* Water surface profile computation with f 
 dw, Uavg 
* Compute energy dissipation 
Hydraulic Analysis
of
Articulated Concrete Blocks
Christopher Thornton, Steven Abt, 
Chad Lipscomb and Michael Robeson 
Recent Developments in the Research and Development 
of Articulating Concrete Blocks for Embankment 
Overtopping Protection 
9
10
Purpose 
* To evaluate the performance of commercially 
available embankment protection systems under 
various hydraulic conditions 
* To develop design criteria for ACB systems 
* To determine the effect of a drainage medium under 
ACB systems 
ACB Mats
Placement 
12
Placement 
Un-Vegetated 
13
Vegetated 
Vegetated 
14
Block Overtopping Tests 
Flume Setup 
1 3 2 
Overtopping Testing 
15
Overtopping Testing 
Threshold Levels 
16
Threshold Levels 
Force Balance 
FR Fi FD FG2 FL FG1 Flow 
Stabilizing Forces 
FR = Interblock resistance 
FG2 = Gravity force normal to slope 
Destabilizing Forces 
Fi = Impact force (projecting block) 
FL = Lift Force 
FD = Drag Force 
FG1 = Gravity force parallel to slope 
17
Design Curves 
0 2 4 6 8 10 12 14 16 18 20 22 24 26 
Velocity (ft/sec) 02468 10 12 14 16 18 20 22 24 26 28 30 
Weight A Weight B Shear Stress (lbft^2) Articulated Concrete Blocks 
Results 
* Drainage layer has pronounced effect on 
system performance 
* At high flows, velocity appears to be 
dominant force 
* Performance values consistent between 
overtopping and channelized test protocols 
Design Criteria
for
Rounded Rock Riprap
Steven Abt 
and 
Humberto Gallegos 
Purpose 
* Develop design criteria for rounded/angular 
rock riprap in overtopping flow 
* Expand the database of rounded rock riprap to 
include higher embankment slopes 
* Increase the understanding of the behavior of 
rounded rock riprap in overtopping flow 
Flume Setup 
From pump # 1 Pump # 2 Rock baffle Riprap Filter layer Soil embankment Main sump 
Lab floor Video platform Wave suppressor Top of flume wall Flow 
Flume Setup 
20
Testing Matrix 
Cumulative Database 
21
Analysis 
y = 0.8505x R2 = 0.9737 0.1 1 10 0.1 1 10 5.23S0.43qf 0.56 D50 C u-0.25[1.0805%R+0.4428]-1 Rounded Angular 
Results 
D = 6.58S0.43qf 0.25(1.0805%R=0.4428) 50 u 
* Embankment Slopes: 10 to 45 % 
* Median Rock Sizes: D50 = 2.4 to 15.3 cm 
* Rounded Rock: 55 to 95 % 
* Riprap Layer Thickness: 1.5 to 3 D50 
* Coefficient of Uniformity: 1.2 to 4.0 
23
B-18
Limited Overtopping, Embankment Breach and Discharge 
Issues, Resolutions & Research Needs Related to Dam Failure Analysis: 
Oklahoma Workshop, June 26-28, 2001 
D.M.TEMPLE and G.J.HANSON, USDA-ARS-PSWCRL, 1301 N. Western, Stillwater, OK. 
74075, Phone (405) 624-4135, E-mail dtemple@pswcrl.ars.usda.gov, and 
ghanson@pswcrl.ars.usda.gov. 
ABSTRACT 
Over 10,000 flood control reservoirs constructed with the assistance of the USDA 
provide almost $1 billion in benefits each year. Sixty-two percent of these 10,000 
structures will reach age 50 by 2020. As these structures age additional trapped 
sediment may reduce the flood control capacity of the reservoir, population increases 
and changes in land in the upstream watershed may result in increased runoff, 
population encroachment on the downstream channels may result in structures that 
were designed to protect agricultural land now being depended upon to protect lives 
and homes, and many state dam safety regulatory requirements have also been 
increased since the original construction as a result of federal legislation and/or state 
laws. Because of this, public safety requires that this aging infrastructure be reevaluated 
and, in some cases, rehabilitated. A key aspect of this re-evaluation is 
prediction of the performance of existing hydraulic structures and channels during 
extreme flood events that may exceed original design conditions. This includes 
prediction of allowable overtopping, rate of embankment breach and failure, and 
resulting discharge. 
INTRODUCTION 
The drought of the 1930s, followed by flooding in the 1940s, made the U.S. agriculture 
community keenly aware of the need to keep the water and soil in place. Following 
World War II, numerous management practices to control erosion and reduce flooding 
were implemented with the assistance of the USDA. Included were the upland flood 
control structures constructed under PL-534, PL-566, Pilot, and RC&D watershed 
programs. Approximately $14 billion was invested in more than 10,000 structures that 
presently provide on the order of $1 billion in benefits annually. These flood control 
structures have become an integral part or the nations transportation and 
communications infrastructure through their protection of roadways, pipelines, etc. 
As these structures continue to age, additional trapped sediment may reduce the flood 
control capacity of many of these reservoirs. Population increases and changes in land 
use have modified the hydrologic properties of the watersheds upstream of some of 
these structures, resulting in increased runoff of water and/or sediment from a given 
storm. Increasing population and encroachment on the downstream channels have 
resulted in structures that were designed to protect agricultural land now being 
depended upon to protect lives and homes. Many state dam safety regulatory 
requirements have also been increased since the original construction as a result of 
federal legislation and/or state laws. Essentially all of the state dam safety laws were 
written or significantly revised after dam safety concerns were raised in the 1970s 
following the failure of Teton and Tacoa Falls Dams. Over 70% of USDA-assisted 
projects were in place by that time. Conflicts between the design of the older dams and 
the new dam safety rules are inevitable. Public safety requires that the aging 
infrastructure that includes these dams be re-evaluated and, in some cases, the dams 
rehabilitated and/or modified if they are to continue to serve public needs. 
The Hydraulic Engineering Research Unit of the ARS Plant Science and Water 
Conservation Research Laboratory is conducting research to address the problems 
associated with rehabilitation of the watershed flood control structures and channels, 
and identified as research objectives. Key identified knowledge deficiencies related to 
rehabilitation of watershed flood control structures and channels may be expressed in 
the form of research objectives as: 1) determination of the extent of overtopping that 
may be sustained by a vegetated earth embankment, such as a dam, without resulting 
in embankment breach, and 2) quantification of the processes associated with breach 
such that timing, rate, and geometry of breach may be predicted, and 3) quantification 
of the discharge hydrograph and peak discharge as a result of an embankment breach. 
The results of this research will be incorporated into evaluation tools and software, 
design criteria, and management practices that will allow the continued service and 
increased benefit of the nations agricultural watershed flood control infrastructure. 
EARTH EMBANKMENT EROSION RESEARCH 
Although the detailed data on embankment overtopping have been very limited, 
substantial data have been gathered from vegetated spillways, which have experienced 
flood flows. Analyses of these data, combined with laboratory tests and analyses, have 
led to the development of a procedure for evaluation of earth spillway performance 
(NRCS, 1997). The model used in this procedure divides the erosion process into three 
phases. These phases are: 1) the failure of the vegetal cover, if any, and the 
development of concentrated flow, 2) erosion in the area of concentrated flow leading to 
the formation of a vertical or near vertical headcut, and 3) the upstream advance of the 
headcut leading to breach which may also be accompanied by further widening and 
deepening. The three phases describing progressive spillway erosion have also been 
observed for erosion of overtopped earth embankments when the embankment material 
exhibits even a small amount of cohesion (Hanson et al 2001). Therefore, even though 
caution is appropriate in attempting to extend this model directly to prediction of 
embankment breach, the breakdown of the process into these same three phases 
would be appropriate. Because of the short distance through the crest or an 
embankment dam, the concept of allowable overtopping is practically limited to the first 
two phases. 
Tests have been conducted to evaluate the effectiveness of un-reinforced vegetation for 
overtopping protection and the applicability, on steep slopes, of the analysis tools of the 
first two phases of the three phase spillway model (Temple and Hanson, 1998; Hanson 
and Temple, 2001). It was found that the vegetation could provide substantial 
protection and that the relations used for phase 1 and phase 2 erosion of spillways 
could be effectively applied to the steeper embankment slopes. Differences observed 
were associated primarily with the reduced flow depth on the steeper slopes. This 
reduction in flow depth reduced the interaction of the vegetal elements with the turbulent 
flow field as a result of the turbulent scales being less than the length of the individual 
elements. However the effect of this on the flow resistance or protective action of the 
grass appeared to be minor. It was also observed that the decrease in flow depth 
emphasized the effects of discontinuities in the cover or surface. The importance of this 
effect on predicting breach or time to breach is shown by the curves of Figure 1 
(reproduced from Temple and Hanson, 2001). 
The equations used in the development of the curves of Figure 1are those documented 
in NRCS (1997) for the limits of phase 1, vegetal, failure. All curves are based on 
computations for a 3:1 embankment slope. Curve a represents a very high quality 
bermudagrass cover over a soil having a plasticity index of 15. Curve b is for that same 
condition except that the cover or surface exhibits minor discontinuities. A minor 
discontinuity is one that is large enough for the turbulent flow to directly impact the 
erodible material, but small enough that the flow does not concentrate within the 
discontinuity. This would normally imply a maximum dimension of the discontinuity 
parallel to flow on the order of flow depth and/or stem length. Curve d is for the same 
condition except that the discontinuity is large enough to allow the flow to fully 
concentrate, thereby negating any protective effect of the vegetal cover. Curve c is 
added to illustrate the relative importance of the material erodibility. Conditions for 
curve c are the same as for curve b except that the plasticity index of the material is 
reduced to zero to represent a highly erodible condition. The effect is substantially less 
than that indicated by adding discontinuities to the cover or surface. In all cases the 
curves represent failure on the slope and do not address the effects of the impacts of 
high velocity flow on toe or berm areas. Figure 1 illustrates that un-reinforced 
vegetation may be effective in providing overtopping protection, but attention must be 
given to maintenance. 
Figure 1. Potential allowable embankment overtopping based on the point of vegetal 
cover failure for: (a) a good cover of Bermuda grass and a material plasticity index of 15; (b) 
a grass cover with minor surface discontinuities and a material plasticity index of 15; (c) 
a grass cover with minor surface discontinuities and a material plasticity index of 0; 
and (d) a grass cover with major discontinuities and a material plasticity index of 15. 
For homogeneous earth embankments, phase 2, concentrated flow erosion, will usually 
represent only a very brief portion of the hydrograph. The combination high stresses 
and low flow depth on the steep embankment slope means that once the flow becomes 
concentrated in the developing discontinuity, erosion to the point of development of a 
vertical or near vertical headcut is normally quite rapid. This phase received some 
attention in the research conducted on steep slopes (Hanson and Temple 2001) and 
embankment overtopping (Hanson et al 2001). These tests verified that phase 2 is 
typically very brief and that the relations used in the spillway model are adequate. An 
important point that was brought out in Hanson and Temple 2001 is that erodibility of 
any given soil may vary several orders of magnitude depending on compaction density, 
and moisture content (Figure 2); indicating that proper measurement of erodibility is 
essential in predicting embankment performance. Erodibility is typically defined by two 
soil parameters, critical stress t c and the detachment coefficient kd. The erosion is 
assumed not to begin until the effective hydraulic stress t e exceeds t c. Once the critical 
stress is exceeded the rate of erosion, de /dt is assumed to occur at a linear rate 
described by the excess stress equation: 
ddt e= kd (t e t - c ) [1] 
t c0 1 2 t ck d (m 3 yl (Pa) Ave =0.55 Pa /N-h) 0.0001 0.001 0.01 0.1 
Laborator Compacted Samples of Soil A 
Embankment Jet Samples 
Estimated Value Based on post test samples 
40 50 60 70 80 90 100 1.4 1.5 1.6 1.7 1.8 1.9 
Saturation % Dry unit wt (Mg/m3) 
Figure 2. Relationship of a) kd and saturation, b) kd and dry unit weight, c) tc and 
saturation, and d) tc and dry unit weight for laboratory jet tests, and embankment jet 
tests. 
Phase 3, headcut deepening and advance, is a critical part of the breaching process. 
The purpose of the spillway model is the determination of the potential for breach to 
occur. Although this is an important consideration for overtopped embankments, the 
time of breach and the outflow from the breach are also important considerations. This 
means that a two-dimensional model (width of eroded area not considered) is not 
adequate, and erosion following the initial breach needs to be considered. This will 
require the addition of a model component to track headcut width during breach 
development and the quantification of at least two additional phases. These additional 
phases are the downward erosion of the crest of the vertical following submergence of 
the headcut and the widening of the headcut following complete local removal of the 
embankment in the vicinity of the breach. Research presently underway includes 
breaching of embankments such as that shown in Figure 3, and will assist in quantifying 
the action that occurs during these additional phases. Laboratory tests confirm that 
material properties may have a major impact on the rate of headcut advance, and 
therefore time to breach and breach rate. The headcut erodibility index based relations 
used in the spillway erosion model are semi-empirical and were developed to cover a 
broad range of geologic conditions. They were also developed without consideration of 
such things as pore water changes with position of the headcut. Therefore, as 
discussed by Hanson et al 2001, it should be possible to either refine the relations for 
application to embankment conditions or to replace this approach with an alternate. 
Work is continuing in this area. The focus to date has been on homogeneous 
embankments, but plans are being made to expand the testing program to include other 
types. 
t = 0 min t = 6 min t = 12 min t = 51 min t = 27 min t = 39 min 
Figure 3. Time series of an embankment breach test of a homogeneous non-plastic 
sandy soil conducted at the ARS Hydraulic Laboratory, Stillwater, OK. 
SUMMARY 
Research efforts at the ARS Plant Science and Water Conservation Research 
Laboratory have resulted in an increased understanding of the erosion processes 
applicable to an overtopped earth embankment. Advances in predicting performance of 
vegetated earth spillways form a point of beginning for quantifying the breach process 
for embankments in a fashion that includes prediction of the extent of overtopping that 
may occur without breach, and the time of breach when breach does occur. However, 
the present spillway model is not considered adequate for this application. 
Additional research is being conducted to allow existing erosion models to be refined 
and extended. With respect to the earth spillway erosion model discussed, this 
involves refinement of existing headcut erosion components and development of 
additional components to address the latter stages of breach development, breach 
widening and breach discharge prediction. Research presently underway will contribute 
to development of these components. 
Research on the ability of un-reinforced vegetation to protect embankment faces has 
shown that grass can substantially increase the time to breach. However, taking 
advantage of this capability will require that attention be given to maintenance of the 
cover and to protecting areas of concentrated attack such as the slope toe. 
Although the research described in this paper focuses on the performance of smaller 
dams of the type constructed with the assistance of the United States Department of 
Agriculture, the results may also be used to better understand the response of larger 
earth dams and will compliment results of research on breach of large dams such as 
that being carried out under the CADAM project (European Commission, 1998a, 1998b, 
1999a, 1999b, 2000). This report discusses the approach being used in USDA 
research, some of the key underlying physical processes that must be considered, and 
the progress being made. 
REFERENCES 
European Commission (1998a) CADAM Concerted Action on Dam Break Modeling, 
Proceedings from the Wallingford Meeting, March 2-3, 1998. 
European Commission (1999b) CADAM Concerted Action on Dam Break Modeling, 
Proceedings from the Munich Meeting, Oct. 8-9, 1998. 
European Commission (1999a) CADAM Concerted Action on Dam Break Modeling, 
Proceedings from the Milan Meeting, May 6-7, 1999. 
European Commission (1999b) CADAM Concerted Action on Dam Break Modeling, 
Proceedings from the Zaragoza Meeting, Nov. 18-19, 1999. 
European Commission (1999b) CADAM Concerted Action on Dam Break Modeling, 
Project Report, H. R. Wallingford. Sept. 2000. CD-ROM. 
Hanson, G. J., Cook, K. R., and Hahn, W. (2001) Evaluating Headcut Migration Rates of 
Earthen Embankment Breach Tests. ASAE paper no. 01-012080. 
Hanson, G. J. and Temple, D. M. (2001) Performance of Bare Earth and Vegetated 
Steep Channels Under Long Duration Flows. ASAE paper no. 01-012157. 
Natural Resources Conservation Service. (1997) Earth spillway erosion model. Chapter 
51, Part 628, National Engineering Handbook. 
Temple, D.M. and Hanson, G.J. (1998) Overtopping of Grassed Embankments. 
Proceedings of the Annual Conference of State Dam Safety Officials, Las Vegas, NV, 
October 11-16, 1998. CD-ROM 
Temple, D.M. and Hanson, G.J. (2001) Water Over the Dam. Prepared for 
Proceedings of the 7th National Watershed Conference, National Watershed Coalition, 
Richmond, VA, May 21-23, 2001. 
B-19
HEC Models for
Dam Break Flood Routing
by
Michael Gee, Ph.D., P.E.
Corps of Engineers Hydrologic Engineering Center 
609 2nd Street, Davis, CA 95616 
(530) 756-1104 
Michael.gee@usace.army.mil 
www.hec.usace.army.mil 
June 2001 Hydrologic Engineering Center 
Hydrologic Engineering Center Mission 
Technical Assistance 
Research and Development 
Training and Software Support 
Center of expertise in hydrologic engineering and planning analysis 
executing a balanced program of research, training and 
technical assistance. Located in Davis, California. 
Hydrologic Engineering Center 
HEC Products
* Hydrologic engineering software; Corps, 
Public, International 
* Technical Methods and Guidance 
* Technical Assistance 
* Prototype studies, Research and Applications 
* Training Courses, Workshops and Seminars 
Some HEC History
* 80s - Simplified techniques, test routing methods 
* 90s 
- NexGen HEC-RAS development for 1-D steady flow 
- UNET (Mississippi Basin Modeling System for 
forecasting) 
- R & U (Alamo Dam, used combination of DAMBRK & 
HEC-RAS 
* 2000s 
- HEC-RAS (unsteady flow) 
- CWMS (Corp Water Management System)
References Hydrologic Engineering Center 
In the early 80s HEC looked at using the TVA explicit model for unsteady 
flow applications. At that time, a geometric pre-processing program (GEDA) 
was developed to compute data tables of geometric properties for USTFLO 
from HEC-2 format cross-sections. This capability was later expanded to 
prepare DAMBRK and DWOPER geometric data from HEC-2 cross sections. 
Research was conducted regarding selection of appropriate flood routing 
procedures (HEC, 1980a) and generalized solutions to dam break flood routing 
(HEC, 1980b). 
UNET (HEC, 2001) has been routinely utilized throughout the Corps for 1-D 
unsteady flow modeling for at least the last fifteen years. Many features have 
been developed by Dr. Barkau for local needs (HEC, 1998). Of particular 
interest and continuing research are issues related to calibration - both 
hydrology related (what is the real flow hydrograph) and hydraulics related 
(what is the appropriate roughness function for the observed stage hydrograph 
and input flow hydrograph). Major developments to UNET (levee breach 
connections to off-channel storage areas, etc.) were prompted by large floods in 
the Mississippi-Missouri system in 93. 
Current HEC work involves incorporation of the UNET unsteady flow equation 
solver into HEC-RAS. This allows the more complete geometric description of 
the river used by RAS to be used as well as RAS graphical displays and data 
editing capabilities. RAS unsteady flow modeling will support the Corps Water 
Management System (HEC, 2000b). 
Schematic of the Alamo Dam study area. A DAMBRK model had been 
developed of this system by the Seattle Dist. Of the Corps (for the L.A. Dist.). 
This model was used to evaluate additional failure scenarios. The DAMBRK 
cross sections were converted into RAS sections so that overbank depths and 
velocities could be computed. RAS was run as a steady flow model using peak 
flows at each section computed by DAMBRK (RAC, 1999). 
Steps to Develop RAS Data
* Start a New Project 
* Enter Geometric data 
* Enter Flow and Boundary data 
* Establish a Plan and Run 
* Evaluate model results 
* Adjust model, as necessary 
Hydrologic Engineering Center 
HEC-RAS Geometric Data 
* River 
* Reach 
* Junctions 
* River Stations 
* Cross section data entry 
Cross-section Data Editor 
* Option: Add Section 
* River-Reach-Station 
* Input section data 
- Station/Elevation Data 
- Reach lengths 
- Mannings n 
- Bank Stations 
- Contract/Expand Coef. 
Hydrologic Engineering Center 
Cross-section Plot 
Profile Plot 
XYZ Perspective Plot 
Use of GIS/DEM data 
RAS cross section data can be developed from a digital terrain model using 
HEC-GeoRAS, which is an extension to ArcView (HEC, 2000a). This figure 
illustrates how the stream centerline and cross section strike lines are chosen by 
the user. This example is Las Vegas Wash. 
Results of HEC-RAS computations can be viewed using the GIS/DEM data 
representation that was used to construct input data. The results that can be 
displayed (mapped) include traditional inundated areas for flows modeled as 
well as depth and velocity distributions. Ongoing work to extend HEC-RAS for 
sediment transport analysis will utilize this information to compute and display 
transverse distributions of bed shear stress and stream power (based upon the 
local grain size). This example is the Salt River near Phoenix, AZ. 
RAS Unsteady Flow
* Overview 
* New Geometric Features for RAS 3.0 
* Geometric pre-processor 
* Boundary and initial conditions 
* Unsteady flow simulation manager 
* Post-processor 
* Additional graphics/tables to view results 
Hydrologic Engineering Center 
Overview
* Common geometry and hydraulic 
computations for steady & unsteady flow 
* Using the UNET equation solver (Dr. 
Robert Barkau) 
* Can handle simple dendritic streams to 
complex networks 
* Able to handle a wide variety of hydraulic 
structures 
* Extremely fast matrix solver 
New Geometric Features for 
HEC-RAS 
* Existing Geometric 
Features all work for 
unsteady flow (XS, 
bridges, Culverts, inline 
weirs/spillways) 
* Lateral Weirs/Spillways 
* Storage Areas 
* Hydraulic Connections 
(weirs, gated spillways, 
and culverts) 
Hydrologic Engineering Center 
All of the existing hydraulic analysis features in the previous steady flow 
versions of HEC-RAS work within the new unsteady flow computation. The 
following new features were added to work with unsteady flow, but they also 
work in the steady flow simulation: 
* Lateral weirs/gated spillways.
* Storage areas: used to model areas of ponded water. 
* Hydraulic connections: use to exchange water between storage areas, storage 
areas and a river reach, and between different river reaches. 
Pre-processing Geometry 
* For unsteady flow, geometry is pre
processed into tables and rating curves 
- Cross sections are processed into tables 
of area, conveyance, and storage 
- Bridges and culverts are processed into a 
family of rating curves for each structure 
- Weirs and gated structures are calculated 
on the fly during unsteady flow calculations 
- Pre-processor results can be viewed in 
graphs and tables 
Hydrologic Engineering Center 
The pre-processor is used to process the geometric data into a series of hydraulic 
properties tables and rating curves. This is done in order to speed up the 
unsteady flow calculations. Instead of calculating hydraulic variables for each 
cross-section during each iteration, the program interpolates the hydraulic 
variables from the tables. The pre-processor must be executed at least once, 
but then only needs to be re-executed if something in the geometric data has 
changed. 
Cross Section Properties Plot 
Cross sections are processed into tables of elevation versus hydraulic properties 
of areas, conveyances, and storage. Each table contains a minimum of 21 points 
(a zero point at the invert and 20 computed values). The user is required to set 
an interval to be used for spacing the points in the cross section tables. The 
interval can be the same for all cross sections or it can vary from cross section to 
cross section. This interval is very important, in that it will define the limits of 
the table that is built for each cross section. On one hand, the interval must be 
large enough to encompass the full range of stages that may be incurred during 
the unsteady flow simulations. On the other hand, if the interval is too large, the 
tables will not have enough detail to accurately depict changes in area, 
conveyance, and storage with respect to elevation. 
Bridge Hydraulic Properties Plot 
Hydraulic structures, such as bridges and culverts, are converted into families of 
rating curves that describe the structure as a function of tailwater, flow and 
headwater. The user can set several parameters that can be used in defining the 
curves. 
Boundary and Initial Conditions
* Boundary conditions must be established 
at all ends of the river system: 
- Flow hydrograph 
- Stage hydrograph 
- Flow and stage hydrograph 
- Rating curve 
- Normal depth
The user is required to enter boundary conditions at all of the external 
boundaries of the system, as well as any desired internal locations, and set the 
initial flow and storage area conditions in the system at the beginning of the 
simulation period. 
Boundary and Initial Conditions
* Interior boundary conditions can also be 
defined within the river system: 
- Lateral inflow to a node 
- Uniform lateral inflow across a reach 
- Ground water inflow 
- Time series of gate openings 
- Elevation controlled gate 
- Observed internal stage and/or flow hydrograph 
Unsteady Flow Simulation Manager 
1. Define a Plan 
2. Select which 
programs to run 
3. Enter a starting and 
ending date and time 
4. Set the computation 
settings 
5. Press the Compute 
button 
Once all of the geometry and unsteady flow data have been entered, the user can 
begin performing the unsteady flow calculations. To run the simulation, go to 
the HEC-RAS main window and select Unsteady Flow Analysis from the Run 
menu. 
The unsteady flow computations within HEC-RAS are performed by a modified 
version of UNET (HEC, 2001). The unsteady flow simulation is actually a three 
step process. First a program called RDSS (Read DSS data) runs. This software 
reads data from a HEC-DSS file and converts it into the user specified 
computation interval. Next, the UNET program runs. This software reads the 
hydraulic properties tables computed by the preprocessor, as well as the 
boundary conditions and flow data from the interface and the RDSS program. 
The program then performs the unsteady flow calculations. The final step is a 
program called TABLE. This software takes the results from the UNET 
unsteady flow run and writes them to a HEC-DSS file. 
Post-processing Results
* Used to compute detailed hydraulic 
information for a set of user-specified 
times and an overall maximum water 
surface profile. 
* Computed stages and flows are passed 
to the steady flow program for the 
computation of detailed hydraulic results 
The Post Processor is used to compute detailed hydraulic information for a set 
of user specified time lines during the unsteady flow simulation period. In 
general, the UNET program only computes stage and flow hydrographs at user 
specified locations. If the Post Processor is not run, then the user will only 
be able to view the stage and flow hydrographs and no other output from 
HEC-RAS. By running the Post Processor, the user will have all of the 
available plots and tables for unsteady flow that HEC-RAS normally produces 
for steady flow. 
When the Post-Processor runs, the program reads from HEC-DSS the maximum 
water surface profile (stages and flows) and the instantaneous profiles. These 
computed stages and flow are sent to the HEC-RAS steady flow computation 
program SNET. Because the stages are already computed, the SNET program 
does not need to calculate a stage, but it does calculate all of the hydraulic 
variables that are normally computed. This consists of over two hundred 
hydraulic variables that are computed at each cross section for each flow and 
stage. 
Viewing Unsteady Flow Results
* All of the output that was available for 
steady flow computations is available for 
unsteady flow (cross sections, profile, and 
perspective plots and tables). 
* Stage and flow hydrographs 
* Time series tables 
* Animation of cross section, profile and 
perspective graphs 
Stage and Flow Hydrographs 
The stage and flow hydrograph plotter allows the user to plot flow hydrographs, 
stage hydrographs, or both simultaneously. Additionally, if the user has 
observed hydrograph data, that can also be plotted at the same time. The plot 
can be printed or sent to the windows clipboard for use in other software. 
Animation of Profile Plot 
Hydrologic Engineering Center 
The HEC-RAS software has the ability to animate the cross section profile. 
When the user selects Animation, the plot steps thought the computed results in 
a timed sequence. The user can control the speed of the animation, as well as 
step through individual time steps. 
Application of HEC-RAS 
to a Dam Break Situation 
Hydrologic Engineering Center 
HEC-RAS (or UNET) can be used to simulate the unsteady routing of flood 
hydrographs resulting from breaching of dams or levees. The user has many 
methods available within the programs to generate the hydrographs. In this 
example, a gate operation is used to mimic the failure of a dam embankment. 
UNET has the ability to compute flows through levee and embankment 
breaches. 
Gate Section 
Gate Operation 
Computed Hydrographs 
Future Work
* Dam & Levee Breaching 
- Overtopping
* Initiation via 
- Water surface elevation 
- Clock (simulation) time 
* Growth rate 
- Linear 
- Exponential 
* Use weir equations with submergence 
Hydrologic Engineering Center 
Weir Type Breach 
Future Work (cont.)
* Dam & Levee Breaching 
- Piping
* Initiation via 
- Water surface elevation 
- Clock (simulation) time 
* Progression 
- Box until top collapses (when top elev. > W.S.) 
* Orifice flow transitioning to weir flow 
Hydrologic Engineering Center 
Piping Type Breach 
Product Availability
* Internal testing (Teton, MBMS etc.) this 
summer 
* General release of HEC-RAS 3.1 - Fall 
of 2001 
* Same breaching algorithms to be used 
in HEC-HMS 
Hydrologic Engineering Center 
REFERENCES 
HEC, 1977, Guidelines for Calculating and Routing a Dam-Break Flood, Research 
Document No. 5, U.S. Army Corps of Engineers, Davis, CA, January 1977. 
HEC, 1980a, Comparative Analysis of Flood Routing Methods, Research Document 
No. 24, U.S. Army Corps of Engineers, Davis, CA, September 1980. 
HEC, 1980b, Dimensionless Graphs of Floods from Ruptured Dams, Research Note 
No. 8, U.S. Army Corps of Engineers, Davis, CA, April 1980. 
HEC, 1995, HEC-DSS Users Guide and Utility Program Manuals, U.S. Army Corps of 
Engineers, Davis, CA. 
HEC, 1998, Mississippi Basin Modeling System Development and Application, Project 
Report No. 36, U.S. Army Corps of Engineers, Davis, CA, April 1998. 
HEC, 2000a, HEC-GeoRAS - An extension of support for HEC-RAS using ArcView, 
Users Manual, CPD-76, U.S. Army Corps of Engineers, Davis, CA, April 2000. 
HEC, 2000b, Corps Water Management System (CWMS), Technical Paper No. 158, 
U.S. Army Corps of Engineers, Hydrologic Engineering Center, June 2000.
HEC, 2001, UNET One-Dimensional Unsteady Flow Through a Full Netwok of Open 
Channels, Users manual, CPD-66, U.S. Army Corps of Engineers, Davis, CA, 
April 2001. 
HEC, 2001, HEC-RAS River Analysis System, Version 3.0 Users Manual, CPD-68, U.S. 
Army Corps of Engineers, Davis, CA, January 2001. 
RAC, 1999, Alamo Dam Demonstration Risk Assessment: Summary Report DRAFT, 
RAC Engineers and Economists and Los Angeles District, U.S. Army Corps of 
Engineers, Davis, CA, January 1977. 
USACE, 1993, River Hydraulics, Engineer Manual 1110-2-1416, Headquarters, U.S. 
Army Corps of Engineers, Washington, DC, October 1993. 
B-20
CADAM & IMPACT:
European Research Projects Investigating Dambreak
Modelling and Extreme Flood Processes
Issues, Resolutions & Research Needs Related to Dam Failure 
Analysis: Oklahoma Workshop, June 26-28, 2001 
M W MORRIS, HR Wallingford, UK 
m.morris@hrwallingford.co.uk 
SYNOPSIS 
This paper provides an overview of the CADAM Concerted Action project, 
which was completed in January 2000, and an introduction to the IMPACT 
research project which will commence November / December 2001. Both 
projects have been funded by the European Commission, with the IMPACT 
project addressing key research issues identified during the CADAM 
concerted action project. 
The Concerted Action project on Dambreak Modelling (CADAM) involved 
participants from 10 different countries across Europe and ran between Feb 
98 and. Jan 2000. The aim of the project was to review dambreak modelling 
codes and practice from first principles through to application, to try and 
identify modelling best practice, effectiveness of codes and research needs. 
Topics covered included the analysis and modelling of flood wave 
propagation, breaching of embankments and dambreak sediment effects. 
The program of study was such that the performance of modelling codes 
were compared against progressively more complex conditions from simple 
flume tests through physical models of real valleys and finally to a real dam-
break test case (the Malpasset failure). The study conclusions are presented 
in a final project report, published by both the EC and the IAHR. This paper 
provides a brief summary of the key issues identified. 
The IMPACT project (Investigation of Extreme Flood Processes & 
Uncertainty) focuses research in a number of key areas that were identified 
during the CADAM project as contributing greatly to uncertainty in 
dambreak and extreme flood predictions. Research areas include 
embankment breach (formation and location), flood propagation 
(infrastructure interaction and urban flooding) and sediment movement 
(near and far zones with respect to embankment failure). The uncertainty 
associated with current predictive models and following project research 
will be demonstrated through application to case study material. 
Implications of prediction uncertainty for end users with applications such 
as asset management and emergency planning will also be investigated. 
MORRIS
CADAM  AN INTRODUCTION 
The first legislation in Europe for dam-break risk analysis was presented in 
France in 1968, following the 1959 Malpasset dam-break that was 
responsible for more than 400 injuries. Since then, and especially more 
recently, many European countries have established legal requirements. 
However the techniques applied when undertaking the specified work can 
vary greatly. The perception of risks related to natural or industrial disasters 
has also evolved, leading to public demand for higher standards of safety 
and risk assessment studies. Considering the relatively high mean 
population density within Europe, a dam-break incident could result in 
considerable injury and damage; efficient emergency planning is therefore 
essential to avoid or minimise potential impacts. 
Dam-break analyses therefore play an essential role when considering 
reservoir safety, both for developing emergency plans for existing structures 
and in focussing planning issues for new ones. The rapid and continuing 
development of computing power and techniques during the last 15 years 
has allowed significant advances in the numerical modelling techniques that 
may be applied to dam-break analysis. 
CADAM was funded by the European Commission as a Concerted Action 
Program that ran for a period of two years from February 1998. Under 
these terms, funding was provided only to pay for travel and subsistence 
costs for meetings, and for project co-ordination. All work undertaken 
during the study was therefore achieved through the integration of existing 
university and national research projects. HR Wallingford co-ordinated the 
project, with additional financial support from the DETR. 
The project continued work started by the IAHR Working Group 
(established by Alain Petitjean following the IAHR Congress in 1995) and 
had the following aims: 
* The exchange of dam-break modelling information between 
participants, with a special emphasis on the links between Universities, 
Research Organisations and Industry. 
* To promote the comparison of numerical dam-break models and 
modelling procedures with analytical, experimental and field data. 
* To promote the comparison and validation of software packages 
developed or used by the participants. 
* To define and promote co-operative research. 
These aims were pursued through a number of objectives: 
* To establish needs of industry, considering a means of identifying dam 
owners, operators, inspectors etc. throughout Europe. 
* To link research with industry needs - encourage participation; 
distribute newsletters to dam owners and other interested parties. 
* To create a database of test cases (analytical, experimental, real life) 
available for reference. 
* To establish the state-of-the-art guidelines and current best practices for 
dam-break modelling within the technical scope of the Concerted 
Action. This leads towards establishing recommended European 
standard methods, procedures and practices for dam-break assessments. 
* To determine future RTD requirements. 
CONCERTED ACTION PROGRAM 
The project involved participants from over 10 different countries across 
Europe. All member states were encouraged to participate, with attendance 
at the program workshops open to all and to expert meetings by 
invitation. Also, links with other experts around the world were welcomed 
to ensure that state-of-the-art techniques and practices were considered. The 
program of meetings planned for the presentation, discussion and 
dissemination of results and information were as follows: 
Meeting 1 Wallingford, UK. 2/3rd March 98(Expert Meeting) 
A review of test cases and modelling work undertaken by the group up to 
the start of CADAM, followed by a review of test cases considered during 
the previous 6 months. Typical test cases included flood wave propagation 
around bends, over obstructions and spreading on a flat surface (physical 
modelling undertaken in laboratory flumes). 
Meeting 2 Munich, Germany 8/9th October 98(Open Workshop) 
Presentations and discussion on the current state of the art in breach 
formation modelling and sediment transport during dam-break events. 
Meeting 3 Milan, Italy May6/7th 99(Expert Meeting) 
Comparison and analysis of numerical model performance against a 
physical model of a real valley (Toce River, Italy) plus an update on breach 
modelling research. 
Meeting 4 Zaragoza, Spain Nov 18/19th 99 (Symposium) 
Comparison and analysis of numerical model performance against a real 
failure test case (Malpasset failure) plus a presentation of the results and 
conclusions drawn from the work of the Concerted Action over the two-year 
study period. 
MODELLING COMPARISONS 
The program of tests progressed from simple conditions to test the basic 
numerical stability of modelling codes, through to a real dambreak test case 
 the Malpasset failure. The aim of the program was to progressively 
increase the complexity of the modelling, and in doing so to try and identify 
MORRIS
which models performed best under which conditions. Both breach models 
and flood routing models were considered during the project. 
Flood Routing Analysis 
Numerical Models The models applied in CADAM ranged from 
commercially available software to codes developed in-house by the 
various participants. Participants ranged from End User organisations such 
as ENEL (Italy), EDF (France) and Vattenfall (Sweden) to consultancy 
companies and universities undertaking research in this field. Many of the 
European participants codes were 2D codes based on depth averaged Saint 
Venant shallow water equations, but applying different numerical schemes 
utilising different orders of accuracy and source term implementations. 
Codes more familiar to the UK market included DAMBRK and ISIS (1D 
model - implicit finite difference Preissmann Scheme). 
Analytical Tests Initial test cases were relatively simple, with analytical
solutions against which the numerical modelling results could be compared.
These tests included:
* Flume with vertical sides, varying bed level and width. No flow 
water at rest. 
* Flume with (submerged) rectangular shaped bump. Steady flow 
conditions. 
* Dam-break flow along horizontal, rectangular flume with a dry bed. 
No friction used. 
* Dam-break flow along horizontal, rectangular flume with a wet bed. 
No friction used. 
* Dam-break flow along horizontal, rectangular flume with a dry bed. 
Friction used. 
These tests were designed to create and expose numerical 'difficulties' 
including shock waves, dry fronts, source terms, numerical diffusion and 
sonic points. Results were presented and discussed at the 2nd IAHR Working 
Group meeting held in Lisbon, Nov. 96 (EDF, 1997). 
Flume Tests Following the analytical tests, a series of more complex tests 
were devised for which physical models provided data (Fig 1). The aim was 
to check the ability of the numerical codes to handle firstly, specific 2D 
features, and then important source terms. These tests were: 
* Dam-break wave along a rectangular flume with 90 bend to the left. 
* Dam-break wave along a rectangular flume with a symmetrical 
channel constriction. 
* Dam-break wave along a rectangular flume expanding onto a wider 
channel (asymmetrical). 
* Dam-break wave along a rectangular flume with 45 bend to the left. 
* Dam-break wave along a rectangular flume with a triangular (weir 
type) obstruction to flow. 
The first three test cases were presented and discussed at the 3rd IAHR 
working Group meeting in Brussels (UCL, June 97) and the remaining two 
at the 1st CADAM meeting in Wallingford (CADAM, March 98). 
downstream upstream Oblique bore 
downstream 
Photos courtesy of Sandra Soares, Universit Catholique de Louvain, Belgium 
Fig. 1 Shock waves generated from dambreak flow around a 45 bend. 
Real Valley Physical Model A model of the Toce River in Italy was used 
for the analysis of model performance against real valley conditions (Fig 
2). The advantage of comparing the numerical models against a physical 
model, at this stage in the project, was that the model data would not include 
any effects from sediment or debris that might mask features of numerical 
model performance. 
Fig. 2 Digital plan model showing the Toce River model 
The model was provided by ENEL and, at a scale of 1:100, represented a 
5km stretch of the Toce River, downstream of a large reservoir. An 
automated valve controlled flow in the model such that a flood hydrograph 
simulating partial or total dam failure could be simulated. Features within 
the downstream valley included a storage reservoir, barrage, bridges and 
villages (Fig 3). 
Photos courtesy of Prof JM Hiver, Universit Libre de Bruxelles, Belgium 
Fig. 3 Bridge structure on the Toce model and a dambreak flow simulation 
Real Failure Test Case  The Malpasset Failure The Malpasset Dam failure 
was selected as the real case study for the project since: 
* The data was readily available through EDF (France) 
* It offered a different data set to the commonly used Teton failure 
* In addition to field observations for peak flood levels there were also 
timings for the failure of three power supply centres 
* Data from a physical model study undertaken by EDF in 1964 (Scale 
1:400) was also available 
Modelling focused on the first 15km of valley downstream of the dam for 
which there was field data to compare against model predictions. This 
stretch of valley included features such as steep sided valleys, side valleys / 
tributaries and bridge / road crossings. 
Breach Analysis 
One of the four CADAM meetings was devoted to breach formation and 
sediment and debris effects. A comparison of the performance of breach 
models was undertaken using two test cases. The first test case was based 
on physical modelling work performed at the Federal Armed Forces 
University in Munich. The simulation tested was for a homogeneous 
embankment represented by a physical model approximately 30cm high. 
The second test case was based on data from the Finnish Environment 
Institute, derived from past collaborative research work undertaken with the 
Chinese. This work analysed the failure of an embankment dam some 5.6m 
high (Loukola et al, 1993). 
SELECTED RESEARCH FINDINGS 
The following sections highlight some selected issues identified during the 
CADAM project: 
Flood Routing 
It was not possible to uniquely define a single best model or single best 
approach for dambreak modelling within the scope of the study since the 
various models and approaches performed differently under varying test 
conditions. Equally, a more in-depth analysis of the significant quantities of 
test data collected is now required to understand some of the performance 
features identified. It was possible, however, to identify some recurring 
features and issues that should be considered when defining best practice for 
dambreak modelling. These include (in no particular order): 
Wave Arrival time The speed of propagation of the flood wave is an 
important component of dambreak modelling since it allows emergency 
planners to identify when inundation of a particular area may be expected. 
It was found that 1D and 2D models failed to reproduce this accurately and 
that 1D models consistently under predicted the time (i.e. flood wave 
propagated too quickly) and 2D models consistently over predicted this time 
(i.e. flood wave propagated too slowly). 
Figure 4 shows wave travel times for one set of test data. The 1D models 
(left) show a scatter of results, probably due to the range of numerical 
methods applied. Results shown spread across the observed data. Later 
tests showed a tendency to under predict the wave speed. Many of the 2D 
models used similar numerical methods perhaps resulting in the tight 
clustering of data, however the results here (and repeated later) show a 
consistent over prediction of wave speed (right). 
20 20 0 0 40t [s] 1 2 3 4 6 5 
0 1020304050 0 1020304050 x [m] x [m] 1 2 3 4 5 80 60 t [s]
Fig. 4 Summary of flood wave travel times for 1D models (left) and 
2D models (right) 
Flood wave speed is poorly modeled  1D models over predict wave speed, 
2D models under predict wave speed. 
Use of 1D or 2D Models It was found that the 1D models performed well 
in comparison with the 2D models for many of the test cases considered. It 
is clear, however, that there are instances where a 2D model predicts 
conditions more effectively than a 1D model. In these situations a 2D model 
should be used or the 1D model should be constructed to allow for 2D 
effects. These situations are where flow is predominantly 2 dimensional 
and include flow spreading across large flat areas (coastal plains, valley 
confluences etc), dead storage areas within valleys and highly meandering 
valleys. Simulation of these features using a 1D model will require 
experienced identification of flow features, reduction of flow cross section 
and addition of headloss along the channel. 
A promising development that may offer a significant increase in model 
accuracy from a 1D model but without the heavy data processing 
requirements of a 2D model, is the use of a patched model. This is where 
areas of 2D flow may be modeled using a 2D approach patched within a 
1D model (Fig 5). This technique requires further development and 
validation, but seems to offer significant potential. 
In relation to the additional effort required for 2D modelling, 1D models 
perform well but cannot be relied upon to simulate truly 2D flow conditions. 
An experienced modeler is required to apply a 1D model correctly to 
simulate some 2D flow conditions. 
Reach 2 b b B Reach 1 aA C c a A c C B 
Reach 3 
Fig. 5 2D patches within a 1D model to improve model accuracy whilst 
limiting processing requirements 
Modeler Assumptions It was clear just from the test cases undertaken (and 
also supported by an independent study undertaken by the USBR (Graham, 
1998)) that the assumptions made by modelers in setting up their models, 
can significantly affect the results produced. Graham (1998) deliberately 
gave identical topographic and structure data to two dambreak modelers 
and asked them to undertake independent dambreak studies for the same 
site. The results varied significantly, and particularly in terms of flood wave 
arrival times. Variations in breach formation, valley roughness and 
simulation of structures contributed to the differences. 
Modelling assumptions can significantly affect the model results. Different 
modelers may produce different results for an identical study. Care should 
be taken to ensure only experienced modelers are used and that all aspects 
and assumptions made are considered. 
Debris and Sediment Effects It is unusual to find debris and sediment effects 
considered in detail for dambreak studies but it is clear from case studies 
and ongoing research that the movement of sediment and debris under 
dambreak conditions can be extreme and will significantly affect 
topography, which in turn affects potential flood levels. Case studies in the 
US have shown bed level variations in the order of 5 to 10m. 
Debris and sediment effects can have a significant impact on flood water 
levels and should be considered during a dambreak study. These effects 
offer a significant source of error in flood prediction. 
Mesh Convergence The definition of a model grid in 2D models, or the 
spacing of cross sections in 1D models, can significantly affect the predicted 
results. Models should be checked as a matter of routine to ensure that the 
grid spacing is appropriate for the conditions modeled and that further 
refinement does not significantly change the modelling results. 
Mesh or section spacing should be routinely checked when modelling 
Breach Modelling 
Existing models are very limited in their ability to reliably predict discharge 
and the time of formation of breaches. Figure 6 below shows a typical 
scatter of modelling results found for the CADAM test cases. Models 
comprised a range of university and commercial codes, including the NWS 
BREACH code. 
It is also clear that there is little guidance available on failure mechanisms of 
structures, which adds to the uncertainty of conditions assumed by 
modelers. 
Fig. 6 Typical scatter of model results trying to predict breach formation 
There are no existing breach models that can reliably predict breach 
formation through embankments. Discharge prediction may be within an 
order of magnitude, whilst the time of breach formation is even worse. 
Prediction of breach formation time due to a piping failure is not yet 
possible. 
The NWS BREACH model is only calibrated against a very limited data set. 
The author (Danny Fread) confirmed that it is based on approximately 5 
data sets. 
Existing breach models should be used with caution and as an indicative 
tool only. A range of parameters and conditions should be modeled to 
assess model performance and results generated. 
There is a clear need to develop more reliable predictive tools that are based 
on a combination of soil mechanics and hydraulic theory. 
End User Needs 
Throughout CADAM, the project focused on the practical needs of end 
users. Attempts were made to quantify a number of issues, both by end 
users and academic researchers alike. The initial response to the question of 
what accuracy models could offer and what was required from end users 
was limited. Without agreement on such issues it is impossible to determine 
whether existing modelling tools are sufficient or not! This perhaps reflects 
the current uncertainty of end users with regards to legislation and 
appropriate safety measures and of modelers appreciation of processes and 
data accuracy. It was suggested that the level of modelling accuracy should 
be appropriate for the site in question (i.e. more detailed for urban areas). 
Water level prediction should be appropriate to the mapping required, and 
the mapping should be at a scale sufficient for emergency planning use (i.e. 
to identify flood levels in relation to individual properties). This suggests an 
inundation mapping scale of approximately 1:5000 for developed areas. 
Inundation maps should be undertaken at a scale appropriate for use in 
emergency planning. For urban areas it is suggested that this should be at a 
scale of 1:5000 or greater. Modelling accuracy should be consistent with the 
detail of mapping required (i.e. for the end user of the data) 
Some Additional Points on DAMBRK_UK and BREACH 
During the project, work undertaken by HR Wallingford identified a number 
of potential problems with the DAMBRK_UK and BREACH software 
packages. 
Under certain conditions, it was found that the DAMBRK_UK package 
created artificial flow volume during the running of a simulation. For the 
limited conditions investigated this volume error was found to be as high as 
+13% (Mohamed (1998)). This error tended to be on the positive side, 
meaning that the flood levels predicted would be pessimistic. It may be 
assumed that similar errors exist in the original DAMBRK code. It was 
noted that model performance varied between DAMBRK, FLDWAV 
(released to replace DAMBRK) and BOSS DAMBRK. A detailed 
investigation into the magnitude and implications of these errors has not yet 
been undertaken. 
Similarly, problems were also found with the BREACH software package. 
Under some conditions, predicted flood hydrographs were found to vary 
significantly with only minor modifications to input parameters. This 
erratic behavior was discovered when considering the differences between 
piping and overtopping failure, by tending the piping location towards the 
crest of the dam. Erratic performance was also confirmed by a number of 
other CADAM members. 
Figure 7 shows a plot of flood hydrographs generated by BREACH for an 
overtopping failure and a piping failure located just 3cm below the crest. 
Logic dictates that these hydrographs should be very similar however the 
results show a significant difference in both the volume of the hydrograph 
as well as the timing. 
MORRIS 12 
Piping Vs Overtopping 
0 0 1 2 3 4 5 6 7 8 9 
Outflow (m3/s) g 500 1000 1500 2000 2500 3000 3500 4000 4500 time Piping Overrtopping
Fig. 7 Different outflow hydrographs produced by breach for an 
overtopping failure and a piping failure located 3cm below the crest. 
CADAM CONCLUSIONS 
The CADAM project has reviewed dambreak modelling codes and practice 
and identified a range of issues relating to model performance and accuracy. 
A number of these issues have been outlined above. When considering all 
aspects contributing to a dambreak study it was found that breach formation 
prediction, debris and sediment effects and modeler assumptions contribute 
greatly to potential prediction errors. 
Full details of all findings and conclusions may be found in the project 
report which has been published by both the EC and the IAHR, and which 
may also be found on the project website at: 
www.hrwallingford.co.uk/projects/CADAM 
BEYOND CADAM 
Following completion of the CADAM project, it was a logical extension of 
the work to review the recommendations and develop a program of 
research work aimed at addressing the key issues. Working within the 
European Commission 5th Framework Research Program, a major 
research proposal was developed by a new consortium of organisations, 
some of whom had worked on the CADAM project and others whom joined 
the team to provide additional and more varied expertise. This proposal was 
named SECURE (Safety Evaluation of Man Made Water Control Structures 
in Europe) 
MORRIS 13 
Funding of European research is undertaken on a competitive basis with a 
finite volume of money with which to fund projects. The original proposal 
initially failed to receive funding and required considerable reworking twice 
before funding was (informally) agreed. During this process the extent of 
the proposed research was significantly reduced. However, the final 
proposal, named IMPACT (Investigation of Extreme Flood Processes & 
Uncertainty), is now subject to contract negotiation with the European 
Commission and research work should commence towards the end of 2001. The following sections are drawn from the European Commission 
discussion documents and provide an overview of the proposed work. 
Whilst the work program is not yet final, it is unlikely to change 
significantly from the work described here. 
THE IMPACT PROJECT - OVERALL AIM 
The problem to be solved in the IMPACT project is to provide means of 
assessing and reducing the risks from the catastrophic failure of dam and 
flood defense structures. 
THE EUROPEAN NEED FOR IMPACT 
In the EU, the asset value of dam and flood defense structures amounts to 
many billions of EURO. These structures include, for example, dams, 
weirs, sluices, flood embankments, dikes, tailings dams etc. Several 
incidents and accidents have occurred which have caused loss of human life, 
environmental and economic damages. For example, in May 1999 a dam 
failed in Southern Germany causing four deaths and over 1 Billion EURO 
of damage. In Spain in 1982, Tous dam failed when still under construction 
with the result of 8 casualties, 100,000 evacuated people and economic 
losses worth 1500 MEuro. In 1997, also in Spain, a dam failed on the 
Guadiamar river, not far from Sevilla, causing immense ecological damage 
from polluted sediments released into the river valley during the failure. The 
dam failure at Malpasset (French riviera) in 1959 caused more than 400 
casualties. 
The risk posed by a structure in any area is a combination of the hazard 
created by the structure (e.g. flooding) and the vulnerability of the potential 
impact area to that hazard (e.g. loss of life, economic loss, environmental 
damage). To manage and minimize this risk effectively it is necessary to be 
able to identify the hazards and vulnerability in a consistent and reliable 
manner. Good knowledge of the potential behavior of the structure is 
important for its proper operation and maintenance in emergency situations 
such as high floods. In addition, prior knowledge of the potential 
consequences of failure of a dam or flood defense structure is essential for 
effective contingency planning to ensure public safety in such an 
emergency. 
In many areas related to structure failure our current understanding and 
ability to predict conditions is limited, so making the management of risk 
difficult. This project aims to advance the risk management process by 
improving knowledge of, and predictive tools for, the underlying processes 
that occur during and after failure. By both improving knowledge of the 
underlying processes and quantifying probability / uncertainty associated 
with these processes, the effect of these processes within the risk 
management system may be demonstrated and subsequently built into 
consideration the risk management process to improve reliability and safety. 
Many of the underlying processes proposed for research were highlighted 
during the recent CADAM European Project as areas requiring further 
research. 
A common problem integral to the failure process is that of sediment and 
debris movement. The sudden release of water from a control structure 
brings with it intensive scour in the flow downstream. Close to the 
structure, the flow is extremely destructive; it can scour aggressively 
material from the riverbed and floor of the valley, changing completely the 
shape of the valley, or even diverting the river from its natural course. The 
flow will uproot vegetation and trees, demolish buildings and bridges and 
wash away animals, cars, caravans etc. The floating debris can be 
transported for substantial distances whilst the heavier material is deposited 
or trapped once the flow velocity attenuates. At a different level, it is the 
erosion of material from an embankment or dam that occurs during 
breaching and hence dictates the rate at which flood water may be released, 
and the location at which this may occur. 
The IMPACT project is of relevance to broad communities of user 
organisations, some of which are Partners in the IMPACT project team. 
The IMPACT project is organised in several complementary and 
interdependent themes to deliver the objectives of the research. 
IMPACT: SCIENTIFIC AND TECHNICAL OBJECTIVES 
The objectives of the IMPACT project are represented schematically in 
Figure 8 below. Specific objectives are therefore to: 
1. Advance scientific knowledge and understanding, and develop 
predictive modelling tools in three key areas associated with the 
assessment of the risks posed by dam and flood defense structures: 
a. the movement of sediment (and hence potential pollutants) generated 
by a failure 
MORRIS 15 
Breach 
Formation 
Flood 
Propagation 
Sediment 
Movement 
Risk Assessment 
Combined inputs with associated 
uncertainty demonstrated through 
case study application 
Implications for End User 
Applications 
Project Co-ordination 
Fig. 8 Structure of the IMPACT work program 
b. the mechanisms for the breaching of embankments (dams or flood 
control dykes) and factors determining breach location 
c. the simulation of catastrophic inundation of valleys and urban areas 
following the failure of a structure 
2. Advance the understanding of risk and uncertainty associated with the 
above factors and combine these factors through a single system to 
demonstrate the risk / uncertainty associated with application of the end 
data (i.e. asset management, emergency planning etc.) 
These objectives will be undertaken with careful reference to past and 
ongoing research projects related to these topics, including the CADAM and 
RESCDAM projects. 
An important subsidiary objective of the IMPACT Partners is to ensure end-
user relevance, acceptance and implementation of the outputs of the 
research. To this end, the IMPACT project Partners will develop the 
methodologies using demonstration sites and applications wherever 
appropriate. The project will include: 
* breaching of large scale test embankments (6m high embankments) to 
investigate breach formation mechanisms and the relationship between 
prototype and laboratory simulation 
* field assessment of sediment movement following large scale 
embankment failure 
* simulation of catastrophic flooding through the streets of a European 
city 
* a combined assessment of extreme flood conditions and prediction 
uncertainty for a real or virtual site comprising dam / flood defense and 
urban area. 
MORRIS 16 
IMPACT: BENEFITS OF THE RESEARCH PROJECT 
The successful completion of the IMPACT project is expected to lead to: 
* improved scientific knowledge and understanding of extreme and 
aggressive flood flows following the catastrophic failure of a water 
control structure 
* Specific scientific knowledge and understanding relating to breach 
formation through dams and flood defense structures, movement of 
sediment under extreme flood conditions and the simulation of flooding 
in urban areas 
* improved understanding of the risk associated with the potential failure 
of dams and flood defense structures ultimately leading to reduced risks 
of failure and hence a reduction in long-term costs 
* improved understanding of the uncertainty associated with the 
prediction of extreme flood conditions and processes 
* improved public safety through emergency planning and community 
disaster preparedness in the event of a failure 
* enhanced prospects for EU-based consultancies in the International 
Water and Hydropower markets 
IMPACT: OVERVIEW OF WORK PROGRAM 
As shown in Figure 8, the IMPACT project has been structured according to 
5 Theme Areas. These Theme Areas are: 
Theme 1 Project Integration, Co-ordination and Delivery 
Theme 2 Breach Formation 
Theme 3 Flood Propagation 
Theme 4 Sediment Movement 
Theme 5 Combined Risk Assessment & Uncertainty 
The objectives and proposed work for each of these Theme Areas is 
presented in more detail below: 
Theme 1 Project Integration, Co-ordination and Delivery 
The IMPACT project involves 9 organizations drawn from 8 European 
countries and thus will require careful attention to the management of the 
research to ensure that it delivers it outputs. The project integration, coordination 
and delivery is a core management function of the project Coordinator. 
The project integration will be achieved through facilitation of 
communication between each of the project themes and the researchers 
engaged in the work packages. There will be a regular meeting of the 
Theme leaders approximately every four to six months. Where possible, 
these meetings will be scheduled with other project meetings to minimize 
the travel costs. Full team meetings will be held at project workshops, of 
which four are scheduled during the 36-month period. These workshops will 
provide opportunities for representatives of all the research teams to discuss 
their findings and future approaches. The Co-ordinator (M Morris: HR 
Wallingford) will use the project workshops to review progress and define 
the detailed work program for the coming months. 
The Co-ordinator will establish a project Internet site with public and 
private areas. The public area will give information on the definitive project 
outputs, whilst the private site with an FTP area will be the main vehicle for 
electronic communication of data, software and results between the 
IMPACT project team members. An Internet based email database will be 
established to allow any interested parties to register their email address for 
receipt of project newsletters, meeting details etc. The Co-ordinator will 
take final responsibility for the documentation and reporting of the project. 
Project team members will be encouraged to publish the results of the 
research in refereed scientific journals and conferences as appropriate. 
Public outputs from the project will be recorded and made available through 
the public area of the project Internet site. 
Theme 2 Breach Formation 
The problem to be solved in this theme is the lack of quantitative 
understanding of the modes and mechanisms involved in the failure of dams 
and flood defense structures. Without such understanding, the rate of 
outflow from a failed structure cannot be assessed and hence the risks posed 
by the structure cannot be assessed with confidence. The approach to the 
research proposed in the IMPACT project is a combination of experimental 
and theoretical investigations, leading to a new modelling procedure for the 
failure of embankments. Three components of failure modes will be 
investigated, internal erosion, overtopping and slope stability during the 
breach enlargement. The methods will be validated as far as possible 
against data from the physical experiments as well as actual failures. The 
large-scale experimental facilities available to the IMPACT partners will 
allow the factors that govern the initiation and growth of breaches to be 
studied under controlled conditions. However, the issue of scaling from the 
laboratory to the prototype scale must be addressed. A novel part of the 
experimental program is the rare opportunity to include field tests at 
large scale. A test site has been identified in Norway located between 
existing dams where a 6m high embankment may be constructed and then 
tested to failure using controlled flow released from the upper dam. Five 
failure tests are planned. The location and test program means that no 
damage to infrastructure will occur, also with minimal environmental effect. 
Individual work packages within this Theme Area include: 
* Breach formation processes  controlled failure of 6m high 
embankments to identify key processes 
* Breach formation processes  laboratory physical modelling of 
embankment failure to identify key processes 
* Model development and comparison -development and comparison of 
breach model performance through use of a common modelling 
framework 
* Breach location  development of a methodology / prototype tool for a 
risk based approach to identifying breach location 
Theme 3 Flood Propagation 
The problem to be solved in this theme is to produce reliable modelling 
methods for the propagation of catastrophic floods generated by the failure 
of a water-control structure (often called the dam-break problem). The 
intensity of the flood will depend upon the initial difference in depth 
between the impounded level behind the control structure and the land level 
on the other side. Hence the research in this theme will concentrate upon 
the dam-break flood problem but the techniques will also be applicable to 
the failure of flood embankments. The overall objectives for this theme are: 
* To identify dam-break flow behavior in complex valleys, around 
infrastructure and in urban areas, and the destructive potential of these 
catastrophic flood waves. 
* To compare different modelling techniques & identify best approach, 
including assessment of accuracy (in relation to practical use of 
software). 
* To adapt existing and develop new modelling techniques for the specific 
features of floods induced by failure of man made structures. 
* To develop guidelines for an appropriate strategy as regards modelling 
techniques, for a reliable and accurate prediction of flooded areas. 
The approach to be adopted is to: 
* compare different mathematical modelling techniques 
* identify the best approaches, including assessment of implementation of 
the methods in industrial software packages 
* check the accuracy and appropriateness of the recommended methods by 
validation of the models against the results from physical 
experimentation. 
* validate the different modelling techniques adopted, both existing and 
newly developed against field data obtained from actual catastrophic 
flood events. 
The research has been organized into two work-packages each subdivided 
into several distinct tasks; for each task there is a Technical Co-ordinator 
and a team of Partners involved in the activities. The two work-packages 
are: 
* Urban flood propagation 
* Flood propagation in natural topographies 
MORRIS 18 
MORRIS 19 
Theme 4 Sediment Movement 
The problem to be solved in this theme is to improve the predictions of the 
motion of sediments in association with catastrophic floods. The nature of 
the problem is different form that in normal flood flows in that the quantity 
and size of sediment will be much greater in the catastrophic flood flow. 
This is an important issue for an accurate prediction of the downstream 
consequences: 
* the river bottom elevation can vary by tens of meters 
* or the river can be diverted from its natural bed (as for the Saguenay 
river tributary  the Lake Ha!Ha! damn failure, Canada, in 1997), 
with the associated impact on the flooded areas. The approach adopted in 
the IMPACT project is to combine physical experiments designed to 
improve our physical understanding of these cases with the development 
and testing of mathematical modelling methods for simulation of these 
flows. The IMPACT Partners will use the extensive experimental facilities 
available to them in undertaking the experimental program. An output of 
the research will be a set of well-documented experimental investigations of 
flows with transported sediment, which could serve the international 
research community as benchmarks for future theoretical developments 
outside the scope of the current IMPACT project. 
The research is divided into two work-packages that address: 
* near field sediment flow in dam-break conditions 
* geomorphological changes in a valley induced by dam-break flows (far 
field) 
Theme 5 Combined Risk Assessment and Uncertainty 
Themes 2-4 outline proposed research into processes that are currently 
poorly understood or poorly simulated by predictive models. An important 
aspect of any process that contributes towards an overall risk assessment 
(i.e. prediction of flood risk) is an understanding of any uncertainty that may 
be associated with prediction of that particular process. For example, a flood 
level may be predicted to reach 20m and an emergency plan developed to 
cope with this. However, if the uncertainty associated with this prediction is 
2m, then different measures may be taken to manage this event. The 
problem to be solved in this theme, is to quantify the uncertainty associated 
with each process contributing to the risk assessment and to demonstrate the 
significance of this for the end application. This may be in the form of 
uncertainty associated with flood level prediction, flood location, flood 
timing or flood volume  depending upon the particular application of data. 
Uncertainty will be quantified by working closely with the fundamental 
research being undertaken in Themes 2-4 and demonstrated through a 
number of case study applications. The procedure for combining the 
uncertainty associated with different data will depend upon the process 
itself. This may require multiple model simulations or combination through 
spreadsheet and / or GIS systems as appropriate. 
Having identified process uncertainty and the effect that particular processes 
may have on the end application, it will also be possible to identify the 
importance (with respect to the accuracy of a risk assessment) that each 
process has and hence the effort that should be applied within the risk 
management process to achieve best value for money. 
IMPACT CONCLUSIONS 
Subject to final contract negotiations with the European Commission, the 
IMPACT project should commence towards the end of 2001 and run for a 
period of 3 years. The research findings from this project should enhance 
understanding of extreme flood processes and simulation including breach 
formation, flood routing and sediment movement. It is intended that 
research undertaken for the IMPACT project shall remain focussed upon the 
needs of end users, and active participation by representatives from industry 
worldwide shall be sought. Technical knowledge relating to the specific 
extreme event processes will be presented but also analysed in the context 
of end user applications with the aim of demonstrating not only what is 
known, but also the uncertainty related to that knowledge and how this 
might influence direct applications. 
For more information on this project, and to sign up to the project email list, 
visit the project website (from November 2001) at: 
www.hrwallingford.co.uk/projects/IMPACT 
or contact the project Co-ordinator directly on: 
m.morris@hrwallingford.co.uk 
ACKNOWLEDGEMENTS 
The members of CADAM are grateful for the financial support offered by 
the European Community to structure this concerted action program. 
Without funding for research time or facilities, however, the project relies 
on contributions made by the group members, which is greatly appreciated. 
The teams who undertook modelling comprise: 
Universit Catholique de Louvain (Belgium), CEMAGREF (France), 
EDF/LNH (France), Universit de Bordeaux (France), INSA Rouen 
(France), Federal Armed Forces University Munich (Germany), ENEL 
MORRIS 21 
(Italy), Politechnika Gdanska (Poland), Universidade Tecnica de Lisboa 
(Portugal), Universidad de Zaragoza (Spain), Universidad Santiago de 
Compostela (Spain), Vattenfall Utveckling AB (Sweden), University of 
Leeds (UK), HR Wallingford (UK). 
Special thanks should also go to the following organisations that have 
undertaken, or made available data from, physical modelling work: 
Universit Catholique de Louvain (Belgium), Universit Libre de Bruxelles 
(Belgium), LNEC (Portugal), ENEL (Italy), Federal Armed Forces 
University Munich (Germany), The Finnish Environment Institute. 
REFERENCES 
EDF (1997). Proceedings of the 2nd AIRH Workshop on Dam-break Wave 
Simulation, Lisbon, Nov. 1996. Report LNH HE-43/97/016/B. 
Universit Catholique de Louvain (1998). Proceedings of the 3nd AIRH 
Workshop on Dam-break Wave Simulation, Brussels, June 1997. 
CADAM (1998). Proceedings of the 1st CADAM workshop, Wallingford, 
March 1998. 
CADAM (1998). Proceedings of the 2nd CADAM workshop, Munich, 
October 1998. 
CADAM (1999). Proceedings of the 3rd CADAM workshop, Milan, May 
1999. 
CADAM (1999). Proceedings of the 4th CADAM workshop, Zaragoza, 
November 1999. 
HR WALLINGFORD (2001). IMPACT: Investigation of Extreme Flood 
Processes & Uncertainty. European Commission proposal document, Part 
B, submitted under the Energy, Environment and Sustainable Development 
Program (Research and Technical Development Activities of a Generic 
Nature), February 2001. 
LOUKOLA E, PAN S (1993). Investigation report on dam safety research 
in China. Finnish co-operative research work on dambreak hydrodynamics, 
National Board of Waters and the Environment Series A 167, 92p. 
MOHAMED (1998) Informatic tools for the hazard assessment of dam 
failure. MSc thesis for Mohamed Ahmed Ali Mohamed, IHE Delft, May 
1998. 
B-21
Issues, Resolutions, And Research Needs Related To Dam Failure Analysis 
USDA/FEMA Workshop 
Oklahoma City June 26 - 28, 2001 
Embankment Breach Research in Norway 
Senior Advisor Kjetil Arne Vaskinn, dr.ing. 
Statkraft Grner AS1 
1. INTRODUCTION 
The modern dam building in Norway started around the turn of the century, when we started to 
exploit our hydropower resources. Hydropower is today one of Norways major natural 
resources. The development of the resource has resulted in construction of many reservoirs. 2500 
dams are controlled by the Norwegian Water Resources and Energy Directorate (NVE). NVE is 
the dam-safety authority in Norway. The dams controlled by NVE are higher than 4 m or have a 
reservoir capacity exceed 0,5 Mill.(m3). 
In the beginning most of the dams was masonry or concrete dams. After 1950, large embankment 
dams began to dominate the scene. 
A water reservoir behind a dam represents an enormous energy potential, which might cause 
catastrophic damage in case of a dam failure. The dams therefore pose a risk to the downstream 
area. To manage and minimize this risk effectively it is necessary to be able to identify the 
hazards and vulnerability in a consistent and reliable manner. Good knowledge of the behavior of 
the structure is important for the maintenance and proper operation. In addition, prior knowledge 
of the potential consequences of failure of a dam or flood defense structure is essential for 
effective contingency planning to ensure public safety. 
The issue of dam safety has become more and more important in Norway during the last years 
and much money has been spent to increase the safety level. The dam owner is responsible for 
the safety of his dams. He has to follow the requirement and guidelines from NVE: 
1 Statkraft Grner is one of the major consulting firms in Norway with 300 employee in 
1998 and an annual turnover 42 mill. US dollar. The company has a high expertise in the 
field of research and development, working closely with academic research groups and the 
hydropower industry. The company is fully owned by Statkraft SF, the largest Hydropower 
Company in Norway. Statkraft SF Operates 55 power plants and has ownership in 36 more. 
The average annual production for Statkraft in Norway is 36 TWh (30% of Norways total). 
Statkraft SF owns 113 water reservoirs with a capacity of 33,7 billion m3 (40% of 
Norways total storage capacity) 
1. Contingency planning for abnormal situations 
2. Safety revisions 
3. Load recording 
4. Damage and accident reporting 
5. Risk analysis 
6. Discussions of the failure probability and studies on impact of failure 
To make sure that the dam-safety work is done in a proper way, NVE has made several 
guidelines. These include Guidelines for simulation of dam-break(Backe et al 1999). All the 
dam-break simulations in Norway are made according to these guidelines. 
The system for revisions of dams, developed by NVE, has been operation for several years. The 
experience so far is good. From time to time the result from a safety revision implies that the 
dam-owners have to put in a lot of money to fulfill the requirements. In most cases this is done 
without any discussions. Sometimes, however, there is a discussion between the owner of a dam 
and NVE based on different understanding of the guidelines and a lack of common understanding 
of the basic mechanism in how the strength and stability of the dam can be improved. The focus 
for discussion is now the new guidelines for dam-safety, not yet put into operation. 
The most frequent theme for discussion is whether or not a dam satisfies the requirement to: 
* Stability when exposed to normal loads. 
* Stability with extreme loads e.g. major leakage and resistance against erosion in case of 
overtopping. 
Stability of rock filled dams is determined mostly as a function of the shear strength of the rock 
filling. Stability in case of extreme loads is also dependent of the shear strength, but in these 
cases there is a big uncertainty in the loads. 
The regulations require that the dams can resist a certain leakage through the core. An ongoing 
project (Cost efficient rehabilitation of dams) also put the focus on the breaching mechanism in 
the case of a major leakage. 
Dam break analysis is performed to assess the consequences of dambreak and is a motivating 
factor for the dam safety work. The routines used today to in Norway give a too simplified 
description of the development in the breach in our rock-filled dams. The materials and the way 
the dam is constructed are not taken into consideration. Due to this most of the work done on the 
dam to improve the security will have no visible influence on the development of the dambreak 
and on the downstream consequences of the break, when performing the dambreak simulation. 
This is not logical and gives not incentives to the dam safety work. The result of this can also be a 
wrong classification of a dam. 
Based on these experiences Norway has started a new project with the main objective of 
improving the knowledge in this field. 
Parallel to the planning of a Norwegian project there, European research institutions have been 
working for establishing a common within the filed of dam-safety. The project is called IMPACT 
and is presented in detail by Mark Morris. The problem to be solved in the IMPACT project is to 
provide means of assessing and reducing the risks from the catastrophic failure of dam and flood 
defense structures (quote from the application to EU for funding of IMPACT). 
2. MAJOR OBJECTIVES 
The scope of the project is to improve the knowledge of, and to develop predictive tools for the 
underlying processes that occur during and failure. By doing so the proper decisions can be taken 
for improving the dam safety taking into account the technology and economy. 
The objectives of the project are: 
* To improve the knowledge on the behavior of rock filled dams exposed to leakage. 
* To get knowledge on the development of a breach. 
This knowledge will be used to: 
* Develop simulation tools that will be used in the planning of dam safety work. 
* Develop new criteria for design of dams 
* Develop criteria for stability and failure mechanics of dams. 
3. PROJECT PLAN. 
The Norwegian project consists of 4 sub-projects: 
1. Shear strengths and permeability of rock-fillings 
2. Stability of the supporting fill and dam-toe in rockfill dams exposed to heavy leakage 
3. Breach formation in embankment-dams (rock-filled dams) 
4. Breach formation in concrete dams 
A rockfill dam is defined as an embankment dam comprising more than 50% by volume of fill 
obtained from rock quarry or rock excavation. (Konov, 2001) 
The IMPACT-project project consist of 4 themes: 
1 Breach Formation 
2 Flood Propagation 
3 Sediment Movement 
4 Combined Risk Assessment and Uncertainty 
Sub-project 3 in the Norwegian project and theme 2 in IMPACT has the same objectives. Some 
of the problems that will be solved in sub-project 1 and 2, will give information that is relevant 
for IMPACT. Through coordination of these to major projects we hope to improve the knowledge 
about embankment dams 
Mark Morris has presented the details of IMPACT. In the following chapters a short description 
of the Norwegian project will be given. 
3.1 Shear strengths and permeability of rock-fillings 
Through the process of reevaluation of rock-filled dams the question of the shear-strength has 
been asked. Very few dams have a documentation of the shear-strength of the rock-fillings based 
on test of the rock materials. In most cases the planning is based on experience from similar dam-
constructions and geological conditions. 
The main question to answer in the project will be what the correct or best parameters to describe 
the materials are. Physical test and experience will be used. Some tests have been done at some of 
the largest rockfill-dams in Norway. This knowledge will be used to correlate the shear-strength 
from single tests of the rock material to roughness, shape of the grains, pressure strength. 
Permeability or hydraulic conductivity is important for the leakage through the supporting fill and 
for the erosion during a dam failure. Existing knowledge and data on this topic will be collected 
through a literature review. Test of the permeability in the large-scale test dam will be performed. 
3.2 Stability of the supporting fill and dam-toe in rock-filled dams exposed to heavy leakage 
Sub-project no 2 will focus on developing of tools or routines for assessment of the stability of a 
dam exposed to leakage through or over the core. 
The objectives of the tests are: 
1. To find the connection between the drainage capacity through a rock-filled dam, the 
size of the stones, layout of the filling/dam-toe etc. This information will be used 
setup of new guidelines for assessment of old dams and for layout and dimensioning 
of new dams in general and specifically the dam-toe. 
2. To increase the knowledge of the permeability of rock-fillings in general. 
3. To find and verify the connection between different scaling. (1:10, 1:5 and prototype) 
A computer simulation program will be developed to analyze the flow through a rock filling. 
Criteria that tells when a rock-filled dam will collapse either due to erosion of the individual 
stones or a major break along shear flater through the supporting fill, will be developed. 
The simulating program will be tested on physical models in large scale 
3.3 Breach formation in rock-filled dams 
The objective of this sub-project is to improve the understanding of the breach formation process 
that occurs in and through embankments, with a special focus on rockfill dams. 
Breach formation covers factors that will lead to an uncontrolled release of water from the 
structure. The most common modes of failure for an embankment are from water overtopping the 
crest or internal erosion also called piping. The ability to predict the location and rate of 
development of a breach through a flood embankment or dam is limited. 
The most commonly applied approach is the deterministic BREACH model developed in the late 
1970s at the US National Weather Service (USNWS). Several parametric relationships based 
upon analysis of actual failures of dams are also in use. In Norway the relationship developed by 
Froelich (Backe D et al.1999) is used. 
Most of the tests and analysis have been of homogeneous structures of non-cohesive material. 
The failure of multi-element structures incorporating an impervious core remains poorly 
understood. 
Experimental tests will be undertaken to support the theoretical development of models of the 
failure modes and rates of failure. These tests will be made as part of the IMPACT project. 
Investigation will be made of the factors contributing to breach location and analysis of the likely 
probability of failure resulting from these factors. 
The tests will be completed through large scale tests. Based on the results from these tests a 
simulation program will be developed for simulation of the breach formation in these kinds of 
dams. 
3.4 Breach formation in concrete dams 
This subproject will focus on the breach formation in concrete dams. Finite element methods will 
be used. The project will take advantage of the experience of concrete technology for simulation 
of failure of concrete dams. 
There exist several very advanced simulation programs that can be used e.g. ABAQUS. This 
program was developed to help engineers to design the off-shore platforms that are used for oil-
drilling in the North Sea. 
4. PHYSICAL/SCALE MODELING 
There will be several test of physical modes in the in the laboratory and in the field (large-scale 
test). This test are necessary in order to find the answers in sub-project 1, 2 and 3 and also for the 
questions asked in theme 2 of IMPACT. 
4.1 Tests in the laboratory. 
There will be laboratory test both in Norway and in UK (Wallingford). The tests in UK will be 
undertaken to examine the different aspects of breach formation. This part of the laboratory 
modeling will use embankments approximately 0.75m in height and the experiments will 
investigate: 
* overtopping failures for water flowing over the crest of an embankment 
* piping failures where fine material is progressively eroded through the body of the 
embankment 
Initial tests will cover homogeneous non-cohesive material  an idealized embankment. Tests 
will then progressively tend towards real embankment designs through the analysis of cohesive 
material and composite structures. Tests will measure flow-rate, the hydraulic heads, and 
evolution of the crest erosion and piping to establish the erosion rates of the material. 
The main issues of the Norwegian laboratory tests are to find out any possible problem with the 
field tests. Several tests of the dam-toe will be made. Focus will be on the following: 
1. Scaling effects 
2. Size of the materials (stones) 
3. Grain size distribution of material 
4. The shape (layout) of the dam-toe 
5. The importance of the downstream-water level. 
In the laboratory we will use to test-flumes: one in the scale 1:5, the second one in scale 1:10. 
According to the plans there will be 13 different tests of the dam-toe. These are shown in table 1. 
Table 1. Tests in the laboratory 
Test no 1 2 3 4 5 6 7 8 9 10 11 12 13 
Scale 1:10 * * * * * * * 1:5 * * * *? *? *? 
Size of the stones D50 [mm] 500 500 100 300 100 0 200 0 100 100 0 500 500 500 500 500 
Sizing E E E E E E E E V E V E E 
Shape Slope 1,5 1,5 1,5 1,5 1,5 1,5 1,5 1,5 1,5 3,0 3,0 1,5 3,0 
Water level L L L L L L L L L L L H H 
Reproducibility t Scale *1 *1 *2 *3 *2 *3 
Size of the stones *1 *2 *1 *1 *1 *1 *2 *2 
Sizing *1 *1 *2 *2 
Slope *1 *2 *1 *2 
H/L water level *1 *2 *1 *2 
E: Uniform, V: well graded, L: low water level downstream, H: high water level downstream
*: referring to which tests can be compared. E.g.: If we want to study the scaling effects, results from test 1 and 2,
2 and 7, and 5 and 8 should be compared.
Key figures for the flumes are shown in table 2. 
Scale 1:10 Scale 1:5 
Width (meter) 2,20 4,0 
Length (meter) 10,0 10,0 
Depth (meter) 0,75 1,43 
Maximum discharge (l/s) 320 600 
We will also make some test with the focus of planning of the field test.
All of the tests in table 1 are used to evaluate the stability of the stones in the outflow area.
Test no 1,2,3,5,7, and 8 will be used to assess if there are some scaling effects. Tests #1 to #8 are 
designed to help in evaluating the effect of the different sizes of the stones in the outflow area. 
The results here will also be used to compare with data from earlier tests and projects: 
* Safety analysis of rock-filed dams, Dam safety project 1992. 
*  Safe remedies for leaking embankment dams, ICOLD, Rio de Janeiro, 1982. 
* Flow through and stability problems in rockfill dams exposed to exceptional loads, Vienna 
1991. 
*  The risk for internal erosion in rock-filled dams and the calculation of turbulent coefficient 
of permeability, Norwegian research Council, 1991. 
* Extreme situations, Short course in dam safety, 1992. 
The test #2, 9, 10 and #11 are identical except from the differences in the grain size distribution 
of the building material. Two of them are well graded. The other two have a uniform grain size 
distribution. These tests will be used to assess the difference in stability with the same 
characteristic size of the stones, but different grain size distribution. 
Table 3 mixing of material 
Table 3.Size of material in prototype 
Test no. Size of stones (mm) mixing 
dmax d60 d50 d10 E/V Cu 
1 750 600 500 240 E 2,5 
2 750 600 500 240 E 2,5 
3 150 120 100 48 E 2,5 
4 400 360 300 144 E 2,5 
5 1500 1200 1000 480 E 2,5 
6 1800 1600 1500 640 E 2,5 
7 150 120 100 48 E 2,5 
8 1500 1200 1000 480 E 2,5 
9 750 600 500 120 V 5 
10 750 600 500 240 E 2,5 
11 750 600 500 120 V 5 
12 750 600 500 240 E 2,5 
13 750 600 500 240 E 2,5 
Tests #2, #9, # 10 and #11is identical except for the slope of the downstream side: two of them 
have the slope of 1:3, the two other have a slope equal to 1:1,5. Results from these tests will be 
used to assess the stability of the toe, due to different slopes. 
Test #2 and #12 are identical, the same is #10 and #13 except for difference in the water-level 
downstream of the dam. These tests will be used to compare the effect on the stability due to 
different level down stream of the dam. 
The following data will be recorded in the tests: 
* The pressure line in the filling 
* Water-level upstream and downstream of the dam 
* The discharge through the dam (measurd downstream of the dam) 
* The water-level at the downstream edge of the dam_toe 
* The grain size distribution curve. 
* The porosity in a test volume 
* Picture from the test 
* Video recording of the test. 
4.2 The field tests 
The field test will be made downstream of one of the largest reservoir in Norway (The lake 
Rssvatnet). Statkraft SF is the owner of this reservoir and is an active partner in the project. The 
test site is in northern Norway, close to the Arctic Circle. Figure 1 
Lysaker/Oslo 
Troms 
Trondheim 
Large scale test-site 
Arctic circle 	
The dam on this reservoir has just been revised. As a result of the safety revision Statkraft SF has 
made safety improvements on the dam. An overview of the area downstream of the dam is shown 
in figure 2. Figure 3 shows cross-section of the test-site and also a longitudinal section along the 
river. So far the focus in the project has been on the laboratory tests. The results from these test 
will give information and knowledge that will be used for the detailed planning 
We are going to run two different kind of tests: 
* tests of the stability of the dam-toe 
* breach tests 
A local contracting firm will be responsible for the building of the dam according to our 
specifications. 
The release of water from the upstream-reservoir has to be done in close cooperation with the 
dam-owner, Statkraft SF. 
The gates at Rssvassdammen have a total capacity up to 500m3/s. The gates are new and the 
operation of them is easy and flexible. The high capacity through the gates gives us the 
opportunity to simulate breaching in a large reservoir (slow reduction in the water level in the 
reservoir as a function of time) and a small reservoir. 
Prior to the tests we will establish a measurement station for discharge. The capacity of the gate 
as a function of the opening is known. By releasing a known discharge through the gates and 
record the corresponding water level a stage-discharge relationship will be established. 
Exact measurement of the discharge through or over the dam is important. 
There might be a minor price to pay for the release of water, because it normally would have 
been use for hydropower production. Negotiation with Statkraft SF is going on now. 
The following data will be recorded in the tests: 
* The pressure line in the filling 
* Water-level upstream and downstream of the dam 
* The discharge through the dam (measured downstream of the dam) 
* The water-level at the downstream edge of the dam_toe 
* Picture from the test 
* Video recording of the test. 
* The development of the breach 
Cross section 
Longitudinal section 
Figure 2 Overview of the test-area. 
Cross-section 
Longitudinal
Figure 3. Cross-section and longitudinal section 
5. BUDGET AND TIME SCHEDULE 
The whole Norwegian project will run for 3 years with the startup the spring 2001 and with a 
total budget of 7 mill Norwegian Kroner. This close to 900 000 Euros. 
6. PARTNERS 
The Statkraft Grner AS is the leader of the Norwegian project and also partner in IMPACT. The 
other Norwegian companies involved are: 
* Norconsult AS 
* NGI (Norwegian Geotechnical Institute) 
* SINTEF Energy Research 
* NTNU (Norwegian University for Science and Technology) 
There is established advisory group or steering committee for the project in Norway. This group 
is made up of the major dam owners in Norway, NVE and the Norwegian Electricity Association 
EBL. 
7. REFERENCES 
BACKE D, (1999), Guidelines for Dam-break simulations. NVE 1-1999. (In Norwegian) 
KONOV T, (2001), Taking Stocks of Norways dams . In International Water Power & Dam 
Construction. Mai 2001. 
SVENDSEN V N and GRTT L. (1995), New Requirements for dam safety in Norway. 
Hydropower & Dams. May 1995. 
C.
PARTICIPANTS 
Steven Abt
Department of Civil Engineering
Colorado State University
Fort Collins, CO 80523-1372
Phone (970) 491-8203
Fax (970) 491-8462
Sabt@engr.ColoState.edu 
Cecil Bearden
Planning and Management Division
Oklahoma Water Resources Board
3800 N. Classen
Oklahoma City, OK 73118
Phone (405) 530-8800
Fax (405) 530-8900
crbearden@owrb.state.ok.us 
David Bowles
Utah State University
Utah Water Research Laboratory
College of Engineering
8200 Old Main Hill
Logan, UT 84322-8200
Phone (435) 797-4010
Fax (435) 797-2663
David.Bowles@usu.edu 
Larry Caldwell
USDA-NRCS
USDA Agricultural Center Bldg.
100 USDA, Suite 206
Stillwater, OK 74074-2655
Phone (405) 742-1257
Fax (405) 742-1126
larry.caldwell@ok.usda.gov 
Catalino Cecilio
Catalino B. Cecilio Consulting
2009 Carignan Way
San Jose, CA 95135-1248
Phone (408) 528-9909
Fax (408) 528-9910
cat@cecilio-consulting.com 
Alton Davis
Engineering Consultants Inc.
12 Old Mill Rd.
P.O. Box 223West Ossipee, NH 03890
Phone (603) 539-8010
Fax (603) 539-4697
apdavis@locanet.com 
Michael Davis 
FERC-Division of Dam Safety and 
Inspections
Chicago Regional Office
230 S. Dearborn St., Suite 3130
Chicago, IL 60604
Phone (312) 353-3787
Fax (312) 353-0109
michael.davis@ferc.fed.us 
James Evans 
FERC-Division of Dam Safety and 
Inspections
888 1st Street NE, Rm. 62-73
Washington, DC 20426
Phone (202) 219-2740
Fax (202) 219-2731
james.evans@ferc.fed.us 
Ellen Faulkner
Mead & Hunt, Inc.
4527 Kensington Court
Eau Claire, WI 54701
Phone (715) 831-9745
faulkner@meadhunt.com 
Ed Fiegle
GA Dept. of Natural Resources
Safe Dams Program
4244 International Pkwy. Ste. 110
Atlanta, GA 30354
Phone (404) 362-2678
Fax (404) 362-2591
ed_fiegle@mail.dnr.state.ga.us 
Danny Fread
622 Stone Road
Westminster, MD 21158
Phone (410) 857-0744
dlfread@starpower.net 
Mike Gee
US Army Corps of Engineers
Hydrologic Engineering Center
609 Second Street
Davis, CA 95616-4587
Phone (530) 756-1104
Fax (530) 756-8250
Michael.Gee@hec01.usace.army.mil 
Wayne Graham
Sediment and River Hyd. Group
Denver Federal Center (D-8540)
Building 67, Room 470
P.O. Box 25007Denver, CO 80225
Phone (303) 445-2553
Fax (303) 445-6351
wgraham@do.usbr.gov 
David Gutierrez 
California Dept. of Water 
P.O. Box 942836Sacramento, CA 94236-0001 
Phone (916) 445-3092 
Fax (916) 227-4759 
daveg@water.ca.gov 
Terry Hampton 
Gannett Fleming 
Manager, Dams and Water Resources Engineering 
8025 Excelsior Drive 
Madison, WI 53717-1900 
Phone (608) 836-1500 
Fax: (608) 831-3337 
thampton@gfnet.com 
Greg Hanson 
USDA-ARS 
1301 N. Western St. 
Stillwater, OK 74075 
Phone (405) 624-4135 x. 224 
Fax (405) 624-4136 
ghanson@pswcrl.ars.usda.gov 
Mikko Houkuna 
Finnish Environment Institute 
P.O. Box 140FIN-00251 Helsinki, Finland 
Phone 011 +358 9 160 3371 
Fax 011 +358 9 160 2417 
Mikko.houkuna@vyh.fi 
Bill Irwin 
USDA, NRCS 
PO Box 2890 
Washington, DC 20013 
Phone (202) 720-5858 
Fax (202) 720-0428 
bill.irwin@usda.gov 
Matt Lindon 
Dam Safety 
State Division of Water Rights 
PO Box 146300 
Salt Lake City, UT 84114-6300 
Phone (801) 538-7372 
Fax (801) 538-7476 
mlindon@state.ut.us 
Martin McCann, Jr. 
Stanford University 
Dept. of Civil and Env. Engineering 
Building 540, Room 124 
Stanford, CA 94305-4020 
Phone (650) 723-1502 
Fax (650) 723-8398 
mccann@ce.stanford.edu 
Mark Morris 
HR Wallingford 
Howberry Park 
Wallingford 
Oxon OX10 8BA, United Kingdom 
Phone +44 (0) 1491 822283 
Fax +44 (0) 1491 825539 
mwm@hrwallingford.co.uk 
David Moser 
Decision Methodologies Division 
Institute for Water Resources 
7701 Telegraph Road 
Alexandria, VA 22315 
Phone (703) 428-8066 
Fax (703) 428-8435 
David.A.Moser@wrc01.usace.army.mil 
Bruce Muller 
Bureau of Reclamation 
U. S. Department of Interior D-6600
P.O. Box 25007Denver, CO 80225 
Phone (303) 445-3238 
bmuller@do.usbr.gov 
John Ritchey 
Dept. of Environmental Protection 
Dam Safety Section 
P.O. Box 419Trenton, NJ 08625
Phone (609) 984-0859
Fax (609) 984-1908
jritchey@dep.state.nj.us 
John Rutledge
Freese & Nichols, Inc.
4055 International Plaza, Suite 200
Fort Worth, TX 76109
Phone (817) 735-7284
Fax (817) 735-7491
jlr@freese.com 
Derek Sakamoto 
Power Supply, MEP, Stave Falls 
Project
6911 Southpoint Dr (E04)
Burnaby, British Columbia
Canada V3N 4X8
Phone (604) 528-7812
Fax (604) 528-1946
Derek.Sakamoto@BCHydro.bc.ca 
Nathan Snorteland 
Bureau of Reclamation 
U. S. Department of Interior D-8311
P.O. Box 25007Denver, CO 80225
Phone (303) 445-2395
nsnorteland@do.usbr.gov 
Darrel Temple
USDA-ARS
1301 N. Western St.
Stillwater, OK 74075
Phone (405) 624-4141 x. 231
Fax (405) 624-4142
dtemple@pswcrl.ars.usda.gov 
Kjetil Arne Vaskinn 
Statkraft Groner AS 
Olav Tryggvasonsgate 
P.O. Box 331NO-7402 Trondheim, Norway
Phone 011 47 83058575
Fax 011 47 73990202
kav@trh.statkraftgroner.no 
Charles Wagner
TVA- River Operations
Sr. Manager, Dam Safety
1101 Market Street LP 3K-C
Chattanooga, TN 37402-2801
Phone (423) 751-6970
Fax (423) 751-6376
cdwagner@tva.gov 
Tony Wahl 
Water Resources Research Lab 
Bureau of Reclamation 
U. S. Department of Interior D-8560
P.O. Box 25007Denver, CO 80225-0007
Phone (303) 445-2155
Fax (303) 445-6324
twahl@do.usbr.gov 
Eugene Zeizel
FEMA
500 C. Street S. W.
Washington, DC 20472
Phone (202) 646-2802
Fax (202) 646-3990
gene.zeizel@fema.gov