Review of sediment gaging efforts in Alameda Creek Lester McKee Alameda Creek Watershed Sediment Forum 951 Turner Ct, Room 230 Hayward, CA December 11, am 4 pm Rationale and objectives ACFC&WCD (the District) expends considerable funds on environmental monitoring ACFC&WCD (the District) expends considerable funds on environmental monitoring Yielded volumes of data to support planning and operations Yielded volumes of data to support planning and operations However, with increasing costs and competition among District programs for limited resources, there is pressure to streamline programs and justify expenditure However, with increasing costs and competition among District programs for limited resources, there is pressure to streamline programs and justify expenditure Cut programs Cut programs Collaborate with others who need similar data to reach their goals Collaborate with others who need similar data to reach their goals Move the District towards the answer to an ultimate question: What is the most cost effective design of the sediment component of the Districts environmental monitoring program? Move the District towards the answer to an ultimate question: What is the most cost effective design of the sediment component of the Districts environmental monitoring program? Data uses Three main categories: Three main categories: Compliance monitoring in relation to environmental laws and policies Compliance monitoring in relation to environmental laws and policies Investigation of pressures on a desired state or the causes of a particular undesirable degraded state in order to respond with management solutions Investigation of pressures on a desired state or the causes of a particular undesirable degraded state in order to respond with management solutions Design of new, or modification of existing facilities Design of new, or modification of existing facilities Data routinely collected by stormwater agencies Could become a shared base program formalized through a (MOU) among agencies Could become a shared base program formalized through a (MOU) among agencies Data for special projects will remain hard to predict separate, discretionary funding Data for special projects will remain hard to predict separate, discretionary funding ClimateRunoffSediment fluxMorphologicalSediment impacts RainfallSurface flowSuspended concentrations and loads Longitudinal profiles Reservoir and weir sediment infilling Pan evaporation Groundwater flow Bed loadCross-section surveys Native and endangered species habitat quality Air temperature Water import and diversions Grain size - Suspended sediment - Bed load sediment - Bed sediment Bank and levee conditions Receiving water body impacts - Sediment loads - Sediment deposition - Turbidity - Contaminant loads Framework of evaluation To evaluate the sediment component of the Districts Environmental Monitoring Program, a framework or set of criteria are needed: To evaluate the sediment component of the Districts Environmental Monitoring Program, a framework or set of criteria are needed: Q1:Are the data representative of reasonable assumptions about temporal variability? Q2:Do the data have historic significance in the District or for the Region as a whole? Q3:Are the data technically sound? Q4:Do the data have multiple uses? Q5:Are the data representative of reasonable assumptions about spatial variability? Q1: Reasonable assumptions about temporal variability? Alameda Creek annual flow coefficient of variation (CV) = 101% Alameda Creek annual flow coefficient of variation (CV) = 101% Rest of North America average CV = 31% Rest of North America average CV = 31% Alameda Creek annual suspended sediment CV = 164% Alameda Creek annual suspended sediment CV = 164% WY , : 9 766,500 metric t (average = 103,100 metric t) WY , : 9 766,500 metric t (average = 103,100 metric t) Bed load even more variable Bed load even more variable So under such variable conditions how do we define success (the point at which we have enough data to characterize wet and dry years) So under such variable conditions how do we define success (the point at which we have enough data to characterize wet and dry years) A rainfall based definition of success? For example define: For example define: Dry:70% MAP Dry:70% MAP Wet:130% MAP Wet:130% MAP For example: For example: 82% chance of capturing a year of 130% MAP with a seven year program 82% chance of capturing a year of 130% MAP with a seven year program 90% chance with a 10 year program 90% chance with a 10 year program (Note this analysis shows that the last 40 years has been wetter on average than the last 105 years) Sediment program running for consecutive years 5-year7-year10-year15-year Probability in the last 40 years (%) Probability in the last 105 years (%) A geomorphic definition of success? For example define a sediment program collecting data at: For example define a sediment program collecting data at: Flow greater than bankfull discharge (BFQ) Flow greater than bankfull discharge (BFQ) Flow greater than effective discharge (ED) Flow greater than effective discharge (ED) But defining BF or ED in California rivers with narrow valleys and/ or incised channels, flashy hydrology and high and variable sediment loads is difficult: But defining BF or ED in California rivers with narrow valleys and/ or incised channels, flashy hydrology and high and variable sediment loads is difficult: Much of the sediment is transported during large floods when landslides and debris flows supply sediment to the channels Much of the sediment is transported during large floods when landslides and debris flows supply sediment to the channels During drier years deposited channel sediment is reworked and transported downstream During drier years deposited channel sediment is reworked and transported downstream Therefore bimodality in sediment transport and channel forming processes is more district in California with large skew in daily flows (Alameda = 12.4) Therefore bimodality in sediment transport and channel forming processes is more district in California with large skew in daily flows (Alameda = 12.4) Effective discharge in northern CA rivers has been reported to range between 1.2 year and 16.1 years (Nolen et al., 1987) so we will use this range to explore the probability of success: Effective discharge in northern CA rivers has been reported to range between 1.2 year and 16.1 years (Nolen et al., 1987) so we will use this range to explore the probability of success: 1 st step: flood frequency analysis (Niles gage WY (n=116)) Success defined by geomorphically relevant floods Sediment program running for consecutive years 5-year7-year10-year15-year Exceed 1.5 year return (1,950 cfs)100 Exceed 2 year return (2,400 cfs)100 Exceed 3.3 year return (6,900 cfs)89100 Exceed 5 year return (9,200 cfs) Exceed 10 year return (13,600 cfs) For example: 89% chance of capturing a year of >6,900 cfs peak flow with a five year program; 100% chance with a 7 year program 85% chance of capturing a year of >9,200 cfs peak flow with a seven year program; 93% chance with a 10 year program Q5: Reasonable assumptions about spatial variability? Two aspects: Two aspects: 1. Ungaged areas Alameda Creek is 98.6% gaged Alameda Creek is 98.6% gaged (near Niles) Ungaged area is Dry Creek which Ungaged area is Dry Creek which given : its small size (23 km 2 or 9 mi 2 ) its small size (23 km 2 or 9 mi 2 ) connectedness connectedness development (24% population increase between ), and development (24% population increase between ), and evidence of landslides and debris flows, evidence of landslides and debris flows, Based on gaging in other urbanizing Bay Area watersheds (Zone 6 Line B and Colma Creek) it may be a significant supply (>31,000 metric t/year or 18% of the sediment load at Niles) Based on gaging in other urbanizing Bay Area watersheds (Zone 6 Line B and Colma Creek) it may be a significant supply (>31,000 metric t/year or 18% of the sediment load at Niles) Photo Credit: Q5: Reasonable assumptions about spatial variability? Two aspects: Two aspects: 2. Geomorphic units Currently operating gages District gages Arroyo De La Laguna at Verona Arroyo De La Laguna at Verona Alameda Creek below Welch Creek near Sunol Alameda Creek below Welch Creek near Sunol Alameda Creek near Niles Alameda Creek near Niles Example of evaluation Alameda Creek near Niles ( ) Q1. Is the data representative of reasonable assumptions about temporal variability? Yes: The data spans water years ranging from the 2nd largest peak flow on record (WY 1958) to the lowest peak annual flow on record (WY 1961). Q2. Does the data have historic significance in the District or for the Region as a whole? Yes: Alameda Creek near Niles is the longest running water and sediment gaging station in the Bay Area. It has significance both locally and regionally. Data from this station teaches us about sediment variability in Bay Area watersheds. It can be used to check the quality of data from any other location in Alameda Creek upstream. Q3. Is the data technically sound? Yes: Mainly because the length of the records smoothes out the errors in SSC and loads estimation. The technical quality of the data has now been improved by the deployment of a turbidity probe in WY The bedload data quality could be improved by ensuring data capture during the peak flood each year. Example of evaluation Alameda Creek near Niles ( ) Q4. Does the data have multiple uses? Yes: The data is useful for learning about habitat quality for salmonids, pre/post project conditions, sediment characterization in relation to sediment disposal or reuse, watershed sediment sources, sources of sediment deposited in the Fremont Flood Control Channel, sediment supply to the Eden Landing restoration area, modeling sediment flux through Niles Canyon, and modeling levee configurations and channel breach scenarios in the Baylands reach. Q.5 Is the data representative of reasonable assumptions about spatial variability? Yes: The data represent almost the whole watershed however the current position of the gage is within a geomorphic unit. Ideally gages would be located in the transitional zones between two units (for example at the head of the canyon or just before the creek exists Niles Canyon). Summary District spends considerable funds annually on environmental monitoring in response to typical needs of an agency charged with management of stormwater District spends considerable funds annually on environmental monitoring in response to typical needs of an agency charged with management of stormwater Given the ongoing and predictable nature of such a base program, there is an opportunity to share costs with other agencies who have overlapping data needs Given the ongoing and predictable nature of such a base program, there is an opportunity to share costs with other agencies who have overlapping data needs If the District were to monitor at a single gage for 10 years, there would have about a 90% chance of capturing a wet year (for example defined as 130%MAP or a 1:5 year return annual flood) If the District were to monitor at a single gage for 10 years, there would have about a 90% chance of capturing a wet year (for example defined as 130%MAP or a 1:5 year return annual flood) The small ungaged area of Dry Creek may be an important supply of sediment directly to the Flood Control Channel The small ungaged area of Dry Creek may be an important supply of sediment directly to the Flood Control Channel The positions of the existing gages are not ideally located in the transition zones between contrasting geomorphic units The positions of the existing gages are not ideally located in the transition zones between contrasting geomorphic units