CPESC Vegetative Stabilization 5 — Questions and Answers
Question 1: Which type of erosion control blanket (ECB) is most appropriate for permanent installation in a channel with moderate flow velocities (2-5 ft/sec) where vegetation is expected to establish through the blanket?
- Photodegradable plastic netting with straw fill
- Biodegradable coconut fiber (coir) blanket with open weave netting (Correct answer)
- Solid impermeable geomembrane liner
- Plastic turf reinforcement mat (TRM) with no organic fill
Correct answer: Biodegradable coconut fiber (coir) blanket with open weave netting
Coir fiber blankets are durable enough for moderate channel flows, biodegrade slowly over 3-5 years, and allow vegetation to root through them for permanent stabilization.
Question 2: What is the primary advantage of using native plant species over non-native species in a permanent vegetative stabilization plan?
- Native species always establish faster than non-native species
- Native species are adapted to local climate and soils, require less maintenance, and support local ecosystems (Correct answer)
- Native species are less expensive to purchase
- Native species provide better erosion control on all slope gradients
Correct answer: Native species are adapted to local climate and soils, require less maintenance, and support local ecosystems
Native species evolved under local conditions and therefore require less irrigation, fertilization, and long-term maintenance while also providing habitat value for native wildlife.
Question 3: A riparian buffer seeding is planned along a perennial stream bank. Which characteristic of the plant species selected is MOST critical for long-term bank stability?
- High seed production for natural reseeding
- Deep, fibrous root systems that bind soil particles (Correct answer)
- Tall canopy height to intercept rainfall
- Rapid above-ground biomass production
Correct answer: Deep, fibrous root systems that bind soil particles
Deep fibrous root systems physically bind soil particles together and increase soil tensile strength, directly resisting the erosive forces of stream flow along the bank.
Question 4: What is 'dormant seeding' and when is it the preferred approach for vegetative stabilization?
- Seeding into dry soil during summer drought to delay germination until fall rains
- Seeding in late fall after soil temperatures drop below germination thresholds so seed germinates the following spring (Correct answer)
- Seeding pre-germinated seed to speed spring establishment
- Seeding shade-tolerant species under existing tree canopy
Correct answer: Seeding in late fall after soil temperatures drop below germination thresholds so seed germinates the following spring
Dormant seeding places seed in soil after frost ends the growing season; seed overwinters and germinates naturally in spring, often producing excellent stands due to good seed-to-soil contact from freeze-thaw cycles.
Question 5: Which practice is used to establish vegetation on extremely steep rock cuts (greater than 1:1) where no soil exists for conventional seeding?
- Standard drill seeding with increased application rates
- Hydraulic application of a soil-seed-fertilizer-mulch mixture bonded with synthetic tackifier or compost to rock surfaces (Correct answer)
- Placement of sod held by wire mesh
- Application of pre-seeded erosion control blankets stapled to the rock
Correct answer: Hydraulic application of a soil-seed-fertilizer-mulch mixture bonded with synthetic tackifier or compost to rock surfaces
Hydro-mulching with a thick slurry containing compost, seed, fertilizer, and tackifier can adhere to bare rock faces and provide a growing medium sufficient for initial plant establishment.
Question 6: After a wildfire burns through a watershed, emergency stabilization seedings are planned. Which grass species would be LEAST appropriate to include in the seed mix due to its invasive potential in western US rangelands?
- Blue grama (Bouteloua gracilis)
- Cheatgrass (Bromus tectorum) (Correct answer)
- Indian ricegrass (Achnatherum hymenoides)
- Western wheatgrass (Pascopyrum smithii)
Correct answer: Cheatgrass (Bromus tectorum)
Cheatgrass is a highly invasive annual grass that dominates post-fire landscapes in the West, outcompetes native species, and dramatically increases wildfire frequency — it must not be included in emergency seedings.
Question 7: What is the recommended staple spacing for securing an erosion control blanket (ECB) on a slope with a gradient steeper than 3:1?
- 6 feet apart in rows 10 feet apart
- 18-24 inches apart in a grid pattern with staples at all overlaps and edges (Correct answer)
- One staple per square yard only at the top anchor trench
- Staples are not required if tackifier is applied over the blanket
Correct answer: 18-24 inches apart in a grid pattern with staples at all overlaps and edges
Steep slopes require closer staple spacing (18-24 inches) in a grid pattern to prevent blanket uplift, displacement, or undercutting by concentrated runoff.
CPESC Vegetative Stabilization 5
Which type of erosion control blanket (ECB) is most appropriate for permanent installation in a channel with moderate flow velocities (2-5 ft/sec) where vegetation is expected to establish through the blanket?