Beaver dams – distribution and impact on water storage in South

- 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 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 ()

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 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