Lake Chesdin VWP Permit 2012

Proposed permit operational rules and analysis of cumulative impacts to beneficial

uses.

Elements of Analysis

Projected Demands• Safe Yield / days of storage remaining

Impact on Beneficial Uses• Water Supply• Downstream aquatic life (IFIM)• On-lake aquatic life• On-lake recreation• Downstream water quality• Downstream water supply

Water Budget: Permitting Period Demands

Historical Maximum monthly withdrawal rate of 47 MGD in 2010

JPA Requests maximum monthly withdrawal of 62 MGD in 2030• 15 MGD = 0.23 inches/day or 7.5 inches per month

Summer-time use ~ 52 MGDprojected in 2030

Figure 2: Withdrawal trends in Lake Chesdin from 2000-2012.

Water Budget: Gage Inflow Statistics

40 MGD use ~ 0.6 in / day Summer evap. rate ~ 0.15 in/day Monthly Patterns:

• July is when the biggest drop in inflows occurs• August is when the lowest single day flows occur• September is when the lowest average monthly

flows occur Recent inflows (2000-2011) are much lower than

historical values (Table 1)Inflow Value Occurrence 1946-2012 Occurrence 2000-2012

190 cfs / 1.8 in 1 out of 5 summers 1 out of 2 summers155 cfs / 1.5 in 1 out of 7 summers 1 out of 3 summers120 cfs / 1.2 in 1 out of 10 summers 1 out of 4 summers 90 cfs / 0.9 in 1 out of 20 summers 1 out of 5 summers43 cfs / 0.4 in 1 out of 50 summers 1 out of 10 summers

Table 1: Comparison of inflows between period 1946-2012 and 2000-2012.

Figure 9: Approximate water level loss, summer evap. & 40 MGD withdrawal.

Climatic Trends: Wet & Dry Periods

Simulations were run for “dry” (2000-2012)& “normal” (1947-2012)

Recent meteorological patterns suggest a pattern of more signif-icant droughts• It is not clear if this is simply a short-term trend or “the

new normal” Dry periods result in more frequent draw-downs,

drought restrictions and reduced in-stream flows.

Figure 4: Linear regression showing trends in minimum annual inflow to Lake Chesdin since 1947.

Beneficial Use Analysis

Predictive modeling of reservoir release rules. IFIM study of downstream aquatic habitat (for Juv. Shad, E.

Complenata , Smallmouth Bass and the Deep-Fast, Deep-Slow, Shallow-Fast, and Shallow-Slow guilds)

Modeling of lake-levels: • impacts to public water supply, • on-lake recreation, and freedom of movement for migratory species.

Monitoring of resident species populations and an analysis of the impact of lake-level fluctuations on them.

Consult with DEQ staff re: the James River Chlorophyll A TMDL & water quality in Appomattox near tidal-fresh James River.

Consulted with DEQ Piedmont Regional Office regarding the South Central Wastewater Treatment plant discharge.

Goals for Reservoir Management

Meet the projected water supply needs of 52.3 MGD during the critical 180 day draw-down period, and 60 days minimum storage during the drought of record.

Minimize loss of downstream habitat (0-20% during normal-high flow conditions and 0-10% during drought).

Minimize long-term (>45 days) closure of fish out-migration, eliminate post October 15th.

Minimize draw-down >2 feet during summer months to preserve on-lake recreation.

Maintain safe-yield (the original 55 MGD).

IFIM Overview

Analysis of downstream habitat based on flows and field surveys

Regulated flows from 60-250 cfs

>10% habitat loss shown to result in negative impacts

Figure 3: Size and Catch Per Unit Effort of largemouth bass as a function of previous year drawdown in Lake Chesdin.

On-Lake: DGIF On-Lake Biota and Drawdown in Lake Chesdin

Littoral species inhabit shallow water areas that change with low lake levels.

In Chesdin, these are primarily sunfish species (largemouth bass and bluegill)

DGIF data since 1986, intensively since 2000

Biologists conclude that drawdown has little to no effect on these littoral species (Fig. 5).

Figure 4: Size and Catch Per Unit Effort of largemouth bass as a function of previous year drawdown in Lake Chesdin.

Proposed Permit Rules

Inflow Release0-60 cfs 100% of Inflow

120-200 cfs 90% of Inflow 60-120 cfs Lesser of 80% of Inflow or Qmax*200+ cfs Lesser of 75% of Inflow or Qmax*

Condition QmaxNormal 250 cfs

Drought Watch or R25 < 0.25 190 cfsDrought Warning or 0.25 < R25 < 0.40 140 cfs

Maximum Release (Qmax*)

Basic Permit Rules

Likelihood of Summertime Drought Flows - R25

Probability of < 25% flow based on winter recharge

Used to reduce max release, • < drawdown • > storm capture

2002 = 54% 2003 = 24% 2012 = 48% Figure 5: Probability of a summertime flow

less than the 25% “non-exceedence” level based on flow November-February.

Permit Effects: Downstream Shad

Median habitat

Current Permit shows 1-5% loss in June, October, ~ 0% loss in other months

Proposed rules limit additional losses to < 8% in all months

Figure 6: Median Juvenile shad habitat for pre-dam, current permit & draft permit rules.

Permit Effects: Downstream Deep Fast Guild

Current Permit shows 15% loss in June, October, <5% loss in other months (including some slight gains)

Proposed 13-20% in June-November

Figure 7: Median Juvenile shad habitat for pre-dam, current permit & draft permit rules.

Permit Effects: Downstream Shallow Fast Guild

Current Permit shows 15% loss in June, October, <5% loss in other months

Proposed 25-35% in Jun-Aug, and Oct. & 17-18% in Sep. and Nov. 

Figure 8: Median Shallow-Fast habitat for pre-dam, current permit & draft permit rules.

On-Lake Recreational Area

Feet Below Full

# Acres > 3 ft Deep

Cumulative % Decrease

0 2,006 0%1 1,776 11%2 1,620 19%3 1,455 27%4 1,343 33%5 1,253 38%

Table 2: Estimated amount of lake area with water > 3 feet deep at various levels of drawdown.

Boating Area available considered to be water > 3 feet deep.

Dock Access: • “Based on feedback from

Chesterfield County and Dinwiddie County … a lake level of 3 to 4 feet below normal pool is … where dock access is significantly impaired. “ (IFIM, 2012)

• Certain areas of lake have impaired dock access at ~18” drawdown (Chesdin Landing).

Permit Effects: On-Lake Recreational Area

Summer months (June-September) with at least 1 day drawn down > 2 ft (<20% loss of rec area)

Dry period > 50% decrease Jun-Jul, 10-20% Aug-Sep Full period > 60% decrease Jun-Jul, 30-40% Aug-Sep

Figure 10: Number of years with draw-downs > 2 ft by month for June-September.

Permit Effects: On-Lake Recreational Area

Summer months (June-September) with at least 1 day drawn down > 1 ft (<11% loss of rec area)

Dry period > 25% decrease Jun&Aug, <10% Jul&Sep Full period > 40% decrease Jun-Jul, 15-20% Aug-Sep

Figure 11: Number of years with draw-downs > 1 ft by month for June-September.

Impacts of Dam Raising

Minimal effects on relative draw-down (i.e. -1 ft) Substantial effects on absolute draw-down (i.e. feet above

sea level)• Increases total recreational area• Decreases incidence of dry-docks

Increase “safe-yield” of reservoir for water supply• 1.5’ rise increases safe yield to ~ 63 MGD (+10 MGD)

Inundation study, necessary• Wetlands impacts• Flood impacts

Guide Curve approach to management useful Sedimentation may reduce gains made by dam raising over

a 25-50 years period.

Additional Permit Info

These are Proposed Permit Rules A storage management plan is required for this

permit issuance.• Sedimentation plan

There will be a provision to monitor & report on procurement of future storage/source acquisition• Demand increases over time• Loss of storage due to sedimentation• Plans for meeting future need.

Potential for provisions that address operations under increased dam level in this permit

Next Steps

Provide draft permit to ARWA. Address any comments they have. Initiate public notice. Depending on comments:

• Issue permit, or• Public hearing -> State Water Control

Board

Common Statistical Measures of Impact

Median – the value which marks the 50% line. For example, if we say:• Median July release is 120 cfs = 50% of release flows are less

than 120 cfs during July• Median July drawdown is 1.5 feet = lake is drawn down more

than 1.5 feet half of the time 10th %ile – the lowest 10% of occurrences. For example:

• 10th %ile August Inflow is 120 cfs = 90% of the time, inflows during August are greater than 120 cfs

10th %ile flow is considered drought warning status in Virginia state plan

Median may be thought of as “chronic”, whereas 10th %ile may be thought of as “acute”