§ 151.001 PURPOSE; AUTHORITY; DISCLAIMER OF LIABILITY.

(A) The purpose of this chapter is to protect, maintain, and enhance the public health, safety, and general welfare by establishing minimum requirements and procedures to control the adverse impacts associated with increased stormwater runoff. The goal is to manage stormwater by using environmental site design (ESD) to the maximum extent practicable (MEP) to maintain after development as nearly as possible, the predevelopment runoff characteristics, and to reduce stream channel erosion, pollution, siltation and sedimentation, and local flooding, and use appropriate structural best management practices (BMPs) only when necessary. This will help restore, enhance, and maintain the chemical, physical, and biological integrity of streams, minimize damage to public and private property, and reduce impacts of land development.

(B) This chapter is adopted pursuant to the Md. Code, Environment Article, Title 4, Subtitle 2, and shall apply to all development occurring within the unincorporated areas of the county. The application of this chapter shall be the minimum stormwater management (SWM) requirements and shall not be deemed a limitation or repeal of any other powers granted by state statute. This county shall be responsible for the coordination and enforcement of this chapter.

(C) The degree of stormwater management (SWM) necessary to satisfy the requirements of this chapter is considered reasonable to regulate the effects of stormwater runoff on the receiving land and water:

(1) Quantity - overbank flood control (Qp10);

(2) Bank erosion - stream capacity (Cpv);

(3) Quality - waterborne pollutants (WQv); and

(4) Local groundwater table - groundwater recharge (Rev).

(D) The amount of protection required is based upon state law, scientific study, and local engineering experience.

(E) Rainfall events beyond the capacity of management measures provided to satisfy this chapter have occurred in the past and may occur in the future. The severity of these events and their effects may be increased by man-made or natural causes.

(F) Implementation of the provisions of this chapter does not create liability on the part of the county or any officer or employee thereof for any damage that may result from reliance on this chapter.

(2004 Code, § 191-1) (Ord. 01-12, passed 9-27-2001; Ord. 04-07, passed 4-1-2004; Ord. 07-08, passed 5-3-2007; Ord. 2010-05, passed 4-29-2010)

§ 151.002 INCORPORATION BY REFERENCE.

For the purpose of this chapter, the following documents are incorporated by reference:

(A) The 2000 Maryland Stormwater Design Manual, Volumes I and II (Maryland Department of the Environment, April, 2000) and all subsequent revisions shall serve as the official guide for stormwater principles, methods, and practices;

(B) United States Department of Agriculture (USDA) Natural Resources Conservation Service Maryland Conservation Practice Standard Pond Code 378 (January, 2000); and

(C) The Carroll County Supplement to the 2000 Maryland Stormwater Design Manual, Volumes I and II, Carroll County Bureau of Resource Management, May, 2010, November, 2018, as amended.

(2004 Code, § 191-2) (Ord. 01-12, passed 9-27-2001; Ord. 04-07, passed 4-1-2004; Ord. 07-08, passed 5-3-2007; Ord. 2010-05, passed 4-29-2010; Ord. 2018-11, passed 11-29-2018)

§ 151.003 DEFINITIONS.

In this chapter the following terms have the meaning indicated. Any term not defined in this chapter shall have the meaning as defined in any chapter of the Carroll County Code (“the Code”). Any term not defined in the Code in any chapter shall have its generally accepted meaning.

ADMINISTRATION. The Maryland Department of the Environment (MDE), Water Management Administration (WMA).

ADVERSE IMPACT. Any deleterious effect on waters or wetlands, including the quality, quantity, surface area, species composition, aesthetics, or usefulness for human or natural uses which are or may potentially be harmful or injurious to human health, welfare, safety, or property, to biological productivity, diversity, or stability or which unreasonably interfere with the enjoyment of life or property, including outdoor recreation.

AGRICULTURAL LAND MANAGEMENT PRACTICES. Those methods and procedures used in the cultivation of land in order to further crop and livestock production and conservation of related soil and water resources.

APPLICANT. An individual, partnership, firm, corporation, or other entity that undertakes or participates in the activities covered by this chapter.

APPROVING AGENCY. The entity responsible for the review and approval of SWM plans (the Bureau of Resource Management, or its successor agency).

AQUIFER. A porous water bearing geologic formation generally restricted to materials capable of yielding an appreciable supply of water.

BASE FLOOD. The runoff that results from the 100-year storm event.

BEST MANAGEMENT PRACTICE (BMP). A structural device or non-structural practice designed to temporarily store or treat stormwater runoff in order to mitigate flooding, reduce pollution, and provide other amenities.

C.F.R. Code of Federal Regulations.

CHANNEL PROTECTION STORAGE VOLUME (Cpv). The volume used to design structural management practices to control stream channel erosion. Methods for calculating the Cpv are specified in the Design Manual.

CLEARING. The removal of trees and brush from the land for development purposes, but not including the mowing of grass or agricultural land management practices.

CHECKLIST. The specific design requirements, organized by project phase, for implementing this chapter.

COMAR. Code of Maryland Regulations.

CONCEPT PLAN. The first of three required plans that includes the information necessary to allow an initial evaluation and approval of a proposed project.

DAM BREACH INUNDATION AREA. The area potentially inundated by a sudden dam failure.

DESIGN MANUAL or MANUAL. The 2000 Maryland Stormwater Design Manual, and all subsequent revisions, that serves as the official guide for SWM principles, methods, and practices.

DETENTION STRUCTURE. A permanent structure for the temporary storage of runoff which is designed so as not to create a permanent pool of water.

DEVELOP LAND. To change the runoff characteristics of a parcel of land in conjunction with residential, commercial, industrial, or institutional construction or alteration. The development of real estate.

DEVELOPER. A person who engages in development or who owns property upon which a development is proposed or accomplished.

DEVELOPMENT. The subdivision of land and those divisions of land referred to as off conveyances, and/or any change to improved or unimproved real estate; including but not limited to: construction; reconstruction; structural alterations; relocation or enlargement of any structure, road, driveway, or appurtenance; grading; dredging; filling; paving; clearing; excavation; dumping; extraction or storage of soil or minerals; the storage of equipment or material.

DRAINAGE AREA. The area contributing runoff to a single point measured in a horizontal plane, which is enclosed by a ridge line.

EASEMENT. A grant or reservation by the owner of land for the use of such land by others for a specific purpose or purposes, and which is included in the conveyance of land affected by such easement.

ENGINEER. A professional engineer licensed in this state, proficient in SWM design.

ENVIRONMENTAL SITE DESIGN (ESD). Using small-scale SWM practices, nonstructural techniques, and better site planning to mimic natural hydrologic runoff characteristics and minimize the impact of land development on water resources. Methods for designing ESD practices are specified in the Design Manual.

EXEMPTION. Those land development activities that are not subject to the SWM requirements contained in this chapter.

EXTENDED DETENTION. A stormwater design feature that provides gradual release of a volume of water in order to increase settling of pollutants and protect downstream channels from frequent storm events. Methods for designing EXTENDED DETENTION BMPs are specified in the Design Manual and the Supplement.

EXTREME FLOOD VOLUME (Qfv). The storage volume required to control those infrequent but large storm events in which overbank flows reach or exceed the boundaries of the 100-year floodplain.

FEMA. Federal Emergency Management Agency.

FINAL STORMWATER MANAGEMENT PLAN. The last of the three required plan submittals that includes the information necessary to allow all reviews, approvals, and permits to be issued by the county.

FLOODPLAIN. The land adjacent to a body of water or stream inundated by the base flood.

FLOW ATTENUATION. Prolonging the flow time of runoff to reduce the peak discharge.

GRADING. Any disturbance of the earth, including but not limited to clearing, stripping, stockpiling, excavating, scarifying, filling, or any combination thereof.

GRADING PERMIT. Written authorization from the county to proceed in accordance with the provisions of Chapter 152.

IMPERVIOUS AREA. Any surface that effectively prevents stormwater from infiltrating into the ground.

INFILTRATION. The passage or movement of water into the soil surface.

LAND SURVEYOR. A professional land surveyor registered in this state, proficient in drainage design.

MAXIMUM EXTENT PRACTICABLE (MEP). Designing SWM systems so that all reasonable opportunities for using ESD planning techniques and treatment practices are exhausted and only where absolutely necessary, a structural BMP is implemented.

OFF SITE STORMWATER MANAGEMENT. The design and construction of a facility necessary to control stormwater from more than one development.

ON SITE STORMWATER MANAGEMENT. The design and construction of systems necessary to control stormwater within an immediate development.

OUTFALL. The point where a storm sewer system discharges.

OVERBANK FLOOD PROTECTION VOLUME (Qpv). The volume controlled by structural practices to prevent an increase in the frequency of out-of-bank flooding generated by development. Methods for calculating the OVERBANK FLOOD PROTECTION VOLUME are specified in the Design Manual and the Supplement.

PERSON. Includes the federal government, the state, any county, municipal corporation, or other political subdivision of the state, or any of their units, or an individual, receiver, trustee, guardian, executor, administrator, fiduciary, or representative of any kind, or any partnership, firm, association, public or private corporation, or any other entity.

PLANNING TECHNIQUES. A combination of strategies employed early in project design to reduce the impact from development and to incorporate natural features into a SWM plan.

POLLUTION or POLLUTANT. Any contamination, or alteration of the physical, chemical, or biological properties of groundwater or surface water, including any change in temperature, taste, color, turbidity, or odor of the waters or the discharge or deposit of any organic matter, harmful organism, or liquid, gaseous, solid, radioactive, or other substance into groundwater or surface water that will render the waters harmful, or detrimental, to public health, safety, or welfare; domestic, commercial, industrial, agricultural, recreational, or other legitimate beneficial uses; livestock, wild animals, birds, fish, or other aquatic life.

RECHARGE VOLUME (Rev). The portion of the water quality volume used to maintain groundwater recharge rates at development sites. Methods for calculating the RECHARGE VOLUME are specified in the Design Manual and the Supplement.

REDEVELOPMENT. Any construction, alteration, or improvement performed on sites where existing land use is commercial, industrial, institutional, or multi-family residential and existing site imperviousness exceeds 40%.

RETENTION STRUCTURE. A permanent structure that provides for the storage of runoff by means of a permanent pool of water.

RETROFITTING. The implementation of ESD practices, the construction of a structural BMP, the modification of an existing structural BMP, or the implementation of a nonstructural practice in a previously developed area to improve water quality over current conditions.

SCD. Soil Conservation District.

SEDIMENT. Soils or other surficial materials transported or deposited by the action of wind, water, ice, or gravity as a product of erosion.

SITE. Any tract, lot, or parcel of land or combination of tracts, lots, or parcels of land, which are in common ownership, or are contiguous and in diverse ownership, where development is to be performed as part of a unit, subdivision, or project.

SITE DEVELOPMENT PLAN. The second of three required plan submittals that includes the information necessary to allow a detailed evaluation and subsequent approval of a proposed project.

SOIL CONSERVATION WATER QUALITY PLAN (SCWQP). A comprehensive plan that covers the entire farm and addresses natural resource management on agricultural lands and utilizes best management practices (BMPs) that control erosion and sediment loss and manage runoff.

STABILIZATION. The prevention of soil movement by any of various vegetative or structural means.

STORM SEWER SYSTEM. A conveyance or system of conveyances, including but not limited to drainage systems, public streets, catch basins, curbs, gutters, ditches, constructed channels, storm drains, associated underground piping, and any on site SWM facilities, that are:

(1) Designed or used for the collection and conveyance of stormwater runoff (either immediate or delayed) from any form of precipitation event;

(2) Not part of a combined sewer system; and

(3) Not part of or discharging into any publicly owned treatment works (POTW) as defined in 40 C.F.R. § 122.2.

STORMWATER. Water that originates from a precipitation event.

STORMWATER MANAGEMENT (SWM).

(1) For quantitative control, a system of vegetative and structural measures that control the increased volume and rate of surface runoff caused by man-made changes to the land; or

(2) For qualitative control, a system of vegetative, structural, and other measures that reduce or eliminate pollutants that might otherwise be carried by surface runoff.

STORMWATER MANAGEMENT PLAN (SWM PLAN). A set of drawings or other documents submitted as a prerequisite to obtaining SWM approval, which contain all of the information and specifications pertaining to SWM.

STORMWATER MANAGEMENT SYSTEM (SWM SYSTEM). Natural areas, ESD practices, SWM measures, and any other structure through which stormwater flows, infiltrates, or discharges from a site.

STREAM. A part of a watercourse either naturally or artificially created that contains intermittent or perennial base flow of groundwater origin, but not including a ditch that conveys surface runoff exclusively from storm events.

STRIPPING. Any activity that removes the vegetative surface cover including tree removal, clearing, grubbing, and storage or removal of topsoil.

SUBDIVISION. Any division of a parcel of land into two or more lots or parcels for the purpose, whether immediate or future, of transfer of ownership, sale, lease, or development.

SUPPLEMENT. The Carroll County Supplement to the 2000 Maryland Design Manual (as amended) that contains administrative procedures, policies, standard designs, and checklists used in the implementation of this chapter.

ULTIMATE STUDY. A hydrologic analysis prepared by a professional engineer or land surveyor and performed to determine the base flood after full development of the contributing watershed, based on existing zoning (ultimate development), and a corresponding hydraulic analysis performed to delineate the ultimate development floodplain (ultimate floodplain).

VARIANCE. The modification of the minimum SWM requirements by the county for specific circumstances where strict adherence to the requirements would result in unnecessary hardship and not fulfill the intent of this chapter.

WAIVER. The reduction of SWM requirements by the county for a specific development on a case-by-case basis:

(1) Qualitative SWM WAIVER includes water quality volume and recharge volume design parameters; and

(2) Quantitative SWM WAIVER includes channel protection storage volume, overbank flood protection volume, and extreme flood volume design parameters.

WATER QUALITY VOLUME (WQv). The volume needed to capture and treat the runoff from 90% of the average annual rainfall at a development site. Methods for calculating the WQv are specified in the Design Manual and the Supplement.

WATERCOURSE. Any natural or artificial stream, river, creek, ditch, channel, canal, conduit, culvert, drain, waterway, gully, ravine, or wash in and including any adjacent area that is subject to inundation from overflow or flood water.

WATERSHED. The total drainage area contributing runoff to a single point.

WETLAND. An area that is inundated or saturated by surface water or groundwater at a frequency and duration sufficient to support, and that under normal circumstances does support, a prevalence of vegetation typically adapted for life in saturated soil conditions, commonly known as hydrophytic vegetation. A WETLAND area is delineated according to the Federal Manual for Identifying and Delineating Jurisdictional Wetlands, 1987 Corps of Engineers Manual.

YEAR (DESIGN) STORM EVENT. A storm that has a specified chance of being equaled or exceeded in any given year. The effective 24-hour rainfall amount to be used for the following design storms (based on National Oceanic and Atmospheric Administration data) will be published in the Supplement and updated annually.

(Design Storm) Year Storm Event	Percent (%) Chance of Being Equaled or Exceeded in Any Given Year
1-Year	99%
2-Year	50%
5-Year	20%
10-Year	10%
25-Year	4%
50-Year	2%
100-Year	1%

(2004 Code, § 191-3) (Ord. 01-12, passed 9-27-2001; Ord. 04-07, passed 4-1-2004; Ord. 07-08, passed 5-3-2007; Ord. 2010-05, passed 4-29-2010; Ord. 2018-11, passed 11-29-2018)

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