Flood impacts on vegetation and hydraulics in ephemeral channels and dynamics of recovery

Figures & data

Figure 1. a) Location of the study sites; b) Nog 1, c) Nog 2, d) Nog Mon, with positions of cross-sections, quadrats (black squares) and crest-stage recorders (X) marked on DEMs derived from ground surveys.

Figure 2. Stage levels measured on the Nogalte site NogMon, 1997–2020.

Figure 3. Photographs of a) mature Retama, b) damaged Retama with large sediment in the base as a result of the 2012 flood, c) remains of Retama, but with some sprouting and seedlings, d) Sprouting of Retama at NogMon site.

Figure 4. Values of velocity and discharge for range of values of Manning n 0.03–0.07, using pre-flood morphology at surveyed cross-sections in each site with most probable values selected.

Table 1. Calculated most probable hydraulic parameters in each reach for pre-flood vegetated state and post-flood minimal vegetated state, using pre- and post-flood morphology, respectively, and for post-flood morphology with vegetated (regrowth) state.

	Manning	Velocity	Discharge	Shear stress	Power	Unit power
	n value	m s^−1	m^3 s^−1	N m^−2	W m^−3	W m^−2
Maximum vegetation state, pre-flood morphology
NOG1	0.07	1.38	24.6	108	4399	181
NOG2	0.07	2.57	321	287	68204	832
NOGMON	0.07	3.22	765	413	182986	1336
Minimum vegetation state, post-flood morphology
NOG1	0.03	4.41	63	185	14851	672
NOG2	0.03	6.55	917	316	170678	2220
NOGMON	0.03	7.48	1770	404	398862	3071
Maximum vegetation state, post-flood morphology
NOG1	0.07	1.89	27	185	6364	228
NOG2	0.07	2.81	393	316	72431	907
NOGMON	0.07	3.2	758	404	170941	1316

Figure 5. Representative cross-section profiles at each site surveyed before and after the 2012 flood, showing the morphological changes.

Figure 6. Nog Mon reach in 2010 (pre-flood), November 2012 (immediate post -flood) and 2019 (after regrowth).

Figure 7. Comparison of example quadrats pre-flood (top row), post-flood (middle row) and in 2020 (bottom row) at Nog 1(left), Nog 2 (middle) and Nog Mon (right).

Figure 8. Changes in % vegetation cover, January 2012 (pre-flood) to January 2020, a) Nog 1, b) Nog 2, c) Nog Mon and peak flow occurrence. VQ = Vegetation Quadrat (as numbered on Figure 1).

Figure 9. Changes in maximum height of plants, January 2012 (pre-flood) to January 2020, a) Nog 1, b) Nog 2, c) Nog Mon and peak flow occurrence.

Figure 10. Values of shear stress calculated for sub-zones within cross-sections for different effects on the plants of the 2012 peak flow, a) Retama, b) Retama, shrubs and herbs.

Figure 11. Changes in state of plants in vegetation groups, Retama, shrubs and herbs, recorded on each vegetation quadrat in the three study sites in the period January 2012-January 2020.

Table 2. Measurements of % cover and maximum regrowth, 2012–2020, grouped by positions of quadrats.

Zone	No. quads	Min % cover	Max % cover	Max growth cm
Inner channel	4	0	10	40
Outer channel	3	2	15	80
Bar	3	10	50	340
Floodplain	2	0	20	72

Figure 12. Growth in a Retama plant on one vegetation quadrat at site NogMon in relation to cumulative amounts of flow as measured by peak stage recorder at the site, a) 2012–2020, b) June 1996–January 2010 (after Hooke and Mant 2015).

Hooke JM, Mant JM. 2015. Morphological and vegetation variations in response to flow events in Rambla channels of SE Spain. In: Dykes AP, Mulligan M and Wainwright J, editors. Monitoring and modelling dynamic environments (A Festschrift in memory of Professor John B. Thornes). Chichester: John Wiley & Sons, p. 61–98.

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