DEPARTMENT OF TRANSPORTATION  
BUREAU OF URBAN AND PUBLIC TRANSPORTATION  
DRAINAGE ASSESSMENTS  
(By authority conferred on the department of state highways and transportation  
and the department of agriculture by section 14a of Act No. 51 of the Public Acts of  
1951, as added, being S247.664a of the Michigan Compiled Laws)  
R 280.1 Definitions.  
Rule 1. (1) "Apportionment" means that portion or share of the total cost of a  
drainage improvement, expressed as a percentage, to be borne by the assessed party by  
reason of benefits to a state highway or county road.  
(2) "Assessment" means the apportionment expressed as a monetary amount.  
(3) "County road" means a roadway, including the right-of-way, under the jurisdiction  
of a county road commission. It includes property contiguous to a roadway owned in fee  
or easement by the county which is used for highway purposes. It does not include  
facilities such as garage sites and office buildings that are not contiguous to the  
highway right-of-way.  
(4) "Department" means the Michigan department  
transportation.  
of  
highways  
and  
(5) "Drainage district" means the total area of land contributing storm water runoff to  
the drain or portion of the drain under consideration.  
(6) "Rainfall intensity" means the rate of rainfall in inches per hour.  
(7) "Runoff" means that part of the rainfall which drains off the land rather than  
being absorbed.  
(8) "Runoff coefficient" means the ratio of the rate of runoff to the rate of rainfall at  
an average storm intensity if all the drainage area is contributing.  
(9) "State highway" means a roadway, including the  
right-of-way,  
under the  
jurisdiction of the department which is part of a designated system of highways. It  
includes property contiguous to the highway owned in fee or in easement by the  
department which is used for highway purposes. It does not include facilities such as  
garage sites and office buildings that are not contiguous to the highway right-of-way.  
History: 1979 AC.  
R 280.2 Computation of basic benefits.  
Rule 2. (1) Basic benefits for county roads and state highways shall be computed in  
direct proportion to the pro rata share of storm water from county roads and state  
highways within the drainage district to the total design storm water runoff from the  
drainage district.  
(2) Storm water runoff quantities (Q) shall be determined for the drainage district  
by use of the accepted engineering formula, Q = ciA, this being the product of the  
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runoff coefficient (c), referred to in table I set forth in R 280.9, the rainfall intensity (i),  
and the area of the drainage district (A). Rainfall intensity is assumed to be of  
uniform rate throughout the drainage district.  
(3) Storm water runoff quantities (Q) for a county road or a state highway shall be  
determined by using the same method as that used for the entire drainage district.  
Computation examples are set forth in R 280.7 and R 280.8.  
(4) If the rainfall intensity used in the design of a county road or a state highway  
drainage facility is not the same as the rainfall intensity used in the design of the  
enclosed receiving county drain or intercounty drain, the basic benefit computed for  
the county road or the state highway shall be multiplied by the number which expresses  
the ratio of the design runoff from the county road or state highway to the design  
runoff for the receiving county or intercounty drain according to the recurrence  
interval factors. (See table II set forth in R 280.9.)  
History: 1979 AC.  
R 280.3 Computation of supplemental benefits.  
Rule 3. (1) Supplemental benefits for county roads and state highways, which shall  
result from maintenance, improvement, or the installation of facilities, structures, or  
mechanical devices jointly determined to be necessary by the highway jurisdiction  
and drain commissioner or drainage board to accommodate or relieve county road  
drainage or state highway drainage, shall be computed in the direct proportion of the  
estimated cost or the actual cost, if known, of such maintenance, improvement,  
facilities, structures, or mechanical devices to the estimated construction cost or  
the actual construction cost, if known, of the total project.  
(2) Supplemental benefits for county roads and state highways, which shall result  
by reason of special specifications or construction conditions required by county  
highway authorities and state highway authorities, shall be computed in the direct  
proportion of the estimated cost or the actual cost, if known, of such special  
specifications or construction conditions to the estimated construction cost or the  
actual construction cost, if known, of the total project.  
History: 1979 AC.  
R 280.4 Apportionments.  
Rule 4. (1) Apportionments to a county for county road benefits and to the  
department for state highway benefits shall be based on benefits computed and  
determined under R 280.2 and R 280.3, except that such apportionments shall not  
include the cost of work performed under R 280.4(2).  
(2) The department or a county road commission may enter into agreements with a  
drain commissioner or drainage board to perform additional work which is not  
subject to these rules. Cost of work performed under such agreements shall not be  
included with the assessments to the department or the county road commission.  
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(3) A county road commission or the department shall be notified of  
its  
apportionments pursuant to Act No. 40 of the Public Acts of 1956, as amended,  
being S280.1 et seq. of the Michigan Compiled Laws.  
History: 1979 AC.  
R 280.5 Assessments.  
Rule 5. (1) Assessments shall be according to the apportioned ratio of the total cost  
of a project.  
(2) If a project is financed by the sale of bonds, evidence that the bonds shall be  
sold shall be presented with the apportionment notice.  
(3) Fifty percent of the cost of drain assessments against a county for drainage of  
county roads shall be paid by the county road commission from county road funds.  
History: 1979 AC.  
R 280.6 Reports.  
Rule 6. Expenditures for county drain assessments shall be reported by each county  
road commission to the state highway commission. The reports shall be made as of  
December 31 of each year and shall be submitted by March 1 of the following year.  
History: 1979 AC.  
R 280.7 Average runoff coefficient; computation examples.  
Rule 7. The following examples demonstrate the desired method of computing  
the average runoff coefficient (A.R.C.) for cross-sections commonly employed in  
the construction of county roads and state highways.  
(a) Cross-section A--dual roadway:  
Figure for 280.7  
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History: 1979 AC.  
R
280.8  
Pro rata share of runoff for county roads and state highways;  
computation examples.  
Rule 8. The computations hereinafter set forth are included to clarify the method by  
which the pro rata share of runoff for county roads and state highways may be  
determined.  
Formula: Q=ciA Q = runoff c = runoff coefficient i = rainfall intensity  
A = area  
Rainfall intensity is assumed to be constant throughout the drainage district,  
according to R 280.2(2), and since the apportionment is based on the pro rata share of  
the runoff, the rainfall intensity has been deleted from these computations.  
(a)  
Computation No. 1:  
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Figure for 280.8 Computation No. 1  
(b) Computation No. 2:  
Figure for 280.8 Computation No. 2  
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(c) Utilities, railroads, or streets may also be subtracted from the total entitled  
"remaining lands," and computed on an equitable "c" factor at the discretion of the  
assessing authority.  
History: 1979 AC.  
R 280.9 Tables.  
Rule 9. The tables referred to in these rules are set forth as follows:  
Figure for 280.9  
History: 1979 AC.  
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;