Beaver dams – distribution and impact on water storage in South Germany
- Study area / methods - Results - Where? - How big?
OTTO; W. - How stable? - How efficent? - Conclusions
Sara Schloemer & Volker Zahner 8. IBS
Floods - nothing new but recently more frequent
• March 1988 • June 1999 • August 2002 • August 2005 • June 2013
Study area
Study area: different geology
Data of dams:
Research in 8 different landscapes photogrametric survey (drone) terrestrial survey of 51 dams
An Bavaria wide inquiry (n= 91)
test area for model prediction 10 years data (Schmidbauer et al. 2006-16) 226 dams/2016
Methods: calculating pond volume
Results: Where built beaver dams?
100% 96% 90% n = 141 80% 70% 60% 50% 40% 30% 20% 10% 4% 0% woodGehölzsaum line noGehölzsaum wood line nicht vorhanden vorhanden
Dam parameters
n = 141
dam height dam height [m]
Dam parameters
n = 141
dam dam wdth [m] dam length dam length [m]
Slope inclination and dam distances
dam Id
Distances Distances between dams [m]
Inclination [%]
Result: the model
Verifying the model prediction (lower Franconia)
80 n = 226 70 67 60 61 60
50
/n
40 dams 30
20 16 11 10 3 5 2 1 0 0 1 2 3 4 5 6 7 8 9 10 Stream width in m
Verifying the model prediction (literature)
lodge without dam lodge with dam
Hartmann & Törnlöv (2006): J. of Zoology Changes in dam numbers due to population rise (lower Franconia)
territories
dams
Number Number of territories / Number of dams
territories dams
Dam perspective
How efficent? Free board and run off (Mangfall river)
freeboard
Freeboard/ cm Freeboard/ L/s off Run
run off
Freeboard and dam stage (~age)
n = 51
Freeboard Freeboard cm /
Prime state Middle state Last state
Permeability of a dam (river Mangfall)
22.02.201722.02.2017
Q = 0.306m³/s
Q = 0.353m³/s
Leandro. J. (2017): TUM How stabile? Flood events and dams (Bohemian forest) n=10
Flood events and dam stabiliy (Bohemian forest)
Flood events and dam stability (Bohemian forest)
run off
10 yrs flood event
run off
/s]
3 3 run off run off [m
How stable? Flood events and dam stability
10 yrs
5 yrs
run off [m3 /s]
Conclusions
• Beavers built dams in small water courses (< 4m, < 0.7 m depth)
• It is possible to model them and their impact on landsacpe level (proactive)
• Dry freebord is one parameter to evaluate the impact on flood reduction
• Dam stability reached its limit at about ~10 years flood event
• Dams are a reaction to enhance habitat or to colonize new areas
• wirken auf Fließgewässern (Grundwasser. Sedimentation. Wasserspeicherung. Fließgeschwindigkeit)
• Wasserrückhalt bei Hochwasser ist Gegenstand von Untersuchungen
Beaver dams - there distribution and impact on water storage in Bavaria Volker Zahner1. Sara Schloemer1 1 University of Applied Sciences Weihenstephan. Germany
Presenter: Volker Zahner. [email protected] Keywords: Dam-building model. water storage. flood mitigation 2nd Session: Beaver and Society or 3 Session: Beaver biology Dam-building is a unique feature of beavers. In this study we tried to find out where and how beavers build dams and created a prediction model out of this. We studied dams in 8 different landscapes and surveyed 51 dams and their surrounding water stretches by photogrammetric and manual techniques. Subsequently dam profiles were generated and exemplary the permeability of a beaver dam was studied by an Acoustic-Doppler-Current-Profiler. In addition. we used information of another 91 dams gathered by an inquiry. The study was designed to find out which impact these dams might have for water storage and which parameters are determining a flood decreasing effect. Dams were built in small streams smaller then 70cm depth. and less than 6-10 m width and with an inclination less than 7 %. 3 to 6 dams in a cascade were normal but up to 21 occurred. The average beaver pond had a volume of 5500 m3 and a surface of 8200 m2. The strongest flood event beaver dams survived in our study were a 10 years flood. Important for the water detain and the mitigation of a flood event was the freeboard which could reach up to 49 cm. Thank you!
Suporter: G. Schwab H. Schwemmer
Dam series parameters
ID Name Catchment Length dam n/ dams Distance of dams Gradient area (km2) series (m) average (m) (%)
102 Hafenlohr 48.2 218.1 8 27.0 6.00 201 Röttelbach 15.8 490.1 8 61.0 0.57 301 Rohrach 18.0 847.1 17 50.0 0.80 302 Wannenbach 2.5 357.0 10 36.0 0.40 303 Moosgraben 6.6 420.0 4 105.0 0.20 503 Kleine Ohe 18.9 113.9 3 38.0 3.50 507 Reschbach 21.3 342.0 9 38.0 5.30 601 Dorfen 75.0 103.0 3 34.3 0.45 701 Glonn-Erd. 0.6 285.5 6 47.6 0.70 801 Mangfall 0.5 463.6 4 115.9 0.75
Changes in territory sizes (lower Franconia)
]
Length of territories [m territories of Length
Dam parameters
Calculating pond volume
Habitate
40 37,5 35 30 26,5 25 19,5 20 15 10 6,5 5,5 5 3,5 1 0